periodic table.docx

The **periodic table**, also known as the **periodic table of the elements**, is an ordered arrangement of the [chemical elements](https://en.wikipedia.org/wiki/Chemical_element) into rows (\"[periods](https://en.wikipedia.org/wiki/Period_(periodic_table))\") and columns (\"[groups](https://en.wikip...

The **periodic table**, also known as the **periodic table of the elements**, is an ordered arrangement of the [chemical elements](https://en.wikipedia.org/wiki/Chemical_element) into rows (\"[periods](https://en.wikipedia.org/wiki/Period_(periodic_table))\") and columns (\"[groups](https://en.wikipedia.org/wiki/Group_(periodic_table))\"). It is an [icon](https://en.wikipedia.org/wiki/Cultural_icon) of [chemistry](https://en.wikipedia.org/wiki/Chemistry) and is widely used in [physics](https://en.wikipedia.org/wiki/Physics) and other sciences. It is a depiction of the [periodic law](https://en.wikipedia.org/wiki/Periodic_trends), which states that when the elements are arranged in order of their [atomic numbers](https://en.wikipedia.org/wiki/Atomic_number) an approximate [recurrence of their properties](https://en.wikipedia.org/wiki/Periodic_function) is evident. The table is divided into four roughly rectangular areas called [blocks](https://en.wikipedia.org/wiki/Block_(periodic_table)). Elements in the same group tend to show similar chemical characteristics. Vertical, horizontal and diagonal [trends](https://en.wikipedia.org/wiki/Periodic_trends) characterize the periodic table. [Metallic](https://en.wikipedia.org/wiki/Metal) character increases going down a group and from right to left across a period. [Nonmetallic](https://en.wikipedia.org/wiki/Nonmetal_(chemistry)) character increases going from the bottom left of the periodic table to the top right. The first periodic table to become generally accepted was that of the Russian chemist [Dmitri Mendeleev](https://en.wikipedia.org/wiki/Dmitri_Mendeleev) in 1869; he formulated the periodic law as a dependence of chemical properties on [atomic mass](https://en.wikipedia.org/wiki/Atomic_mass). As not all elements were then known, there were gaps in his periodic table, and Mendeleev successfully used the periodic law to [predict some properties of some of the missing elements](https://en.wikipedia.org/wiki/Mendeleev%27s_predicted_elements). The periodic law was recognized as a fundamental discovery in the late 19th century. It was explained early in the 20th century, with the discovery of [atomic numbers](https://en.wikipedia.org/wiki/Atomic_number) and associated pioneering work in [quantum mechanics](https://en.wikipedia.org/wiki/Quantum_mechanics), both ideas serving to illuminate the internal structure of the atom. A recognisably modern form of the table was reached in 1945 with [Glenn T. Seaborg](https://en.wikipedia.org/wiki/Glenn_T._Seaborg)\'s discovery that the [actinides](https://en.wikipedia.org/wiki/Actinide) were in fact f-block rather than d-block elements. The periodic table and law are now a central and indispensable part of modern chemistry. The periodic table continues to evolve with the progress of science. In nature, only elements up to atomic number 94 exist;[^\[a\]^](https://en.wikipedia.org/wiki/Periodic_table#cite_note-transuranium-1) to go further, it was necessary to [synthesize](https://en.wikipedia.org/wiki/Synthetic_element) new elements in the laboratory. By 2010, the first 118 elements were known, thereby completing the first seven rows of the table;[^\[1\]^](https://en.wikipedia.org/wiki/Periodic_table#cite_note-2) however, chemical characterization is still needed for the heaviest elements to confirm that their properties match their positions. New discoveries will extend the table [beyond these seven rows](https://en.wikipedia.org/wiki/Extended_periodic_table), though it is not yet known how many more elements are possible; moreover, theoretical calculations suggest that this unknown region will not follow the patterns of the known part of the table. Some scientific discussion also continues regarding whether some elements are correctly positioned in today\'s table. Many [alternative representations](https://en.wikipedia.org/wiki/Alternative_periodic_tables) of the periodic law exist, and there is some discussion as to whether there is an optimal form of the periodic table. **Structure** - [v](https://en.wikipedia.org/wiki/Template:Periodic_table) - [t](https://en.wikipedia.org/wiki/Template_talk:Periodic_table) - [e](https://en.wikipedia.org/wiki/Special:EditPage/Template:Periodic_table) **Periodic table** Group 1 2   3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 Hydrogen &amp; alkali metals Alkaline earth metals Triels Tetrels Pnicto­gens Chal­co­gens Halo­gens Noble gases Period 1 Hydro­gen1H​1.0080 He­lium2He​4.0026 2 Lith­ium3Li​6.94 Beryl­lium4Be​9.0122 Boron5B​10.81 Carbon6C​12.011 Nitro­gen7N​14.007 Oxy­gen8O​15.999 Fluor­ine9F​18.998 Neon10Ne​20.180 3 So­dium11Na​22.990 Magne­sium12Mg​24.305 Alumin­ium13Al​26.982 Sili­con14Si​28.085 Phos­phorus15P​30.974 Sulfur16S​32.06 Chlor­ine17Cl​35.45 Argon18Ar​39.95 4 Potas­sium19K​39.098 Cal­cium20Ca​40.078 Scan­dium21Sc​44.956 Tita­nium22Ti​47.867 Vana­dium23V​50.942 Chrom­ium24Cr​51.996 Manga­nese25Mn​54.938 Iron26Fe​55.845 Cobalt27Co​58.933 Nickel28Ni​58.693 Copper29Cu​63.546 Zinc30Zn​65.38 Gallium31Ga​69.723 Germa­nium32Ge​72.630 Arsenic33As​74.922 Sele­nium34Se​78.971 Bromine35Br​79.904 Kryp­ton36Kr​83.798 5 Rubid­ium37Rb​85.468 Stront­ium38Sr​87.62 Yttrium39Y​88.906 Zirco­nium40Zr​91.224 Nio­bium41Nb​92.906 Molyb­denum42Mo​95.95 Tech­netium43Tc​ Ruthe­nium44Ru​101.07 Rho­dium45Rh​102.91 Pallad­ium46Pd​106.42 Silver47Ag​107.87 Cad­mium48Cd​112.41 Indium49In​114.82 Tin50Sn​118.71 Anti­mony51Sb​121.76 Tellur­ium52Te​127.60 Iodine53I​126.90 Xenon54Xe​131.29 6 Cae­sium55Cs​132.91 Ba­rium56Ba​137.33 1 asterisk Lute­tium71Lu​174.97 Haf­nium72Hf​178.49 Tanta­lum73Ta​180.95 Tung­sten74W​183.84 Rhe­nium75Re​186.21 Os­mium76Os​190.23 Iridium77Ir​192.22 Plat­inum78Pt​195.08 Gold79Au​196.97 Mer­cury80Hg​200.59 Thallium81Tl​204.38 Lead82Pb​207.2 Bis­muth83Bi​208.98 Polo­nium84Po​ Asta­tine85At​ Radon86Rn​ 7 Fran­cium87Fr​ Ra­dium88Ra​ Lawren­cium103Lr​ Ruther­fordium104Rf​ Dub­nium105Db​ Sea­borgium106Sg​ Bohr­ium107Bh​ Has­sium108Hs​ Meit­nerium109Mt​ Darm­stadtium110Ds​ Roent­genium111Rg​ Coper­nicium112Cn​ Nihon­ium113Nh​ Flerov­ium114Fl​ Moscov­ium115Mc​ Liver­morium116Lv​ Tenness­ine117Ts​ Oga­nesson118Og​ 1 asterisk Lan­thanum57La​138.91 Cerium58Ce​140.12 Praseo­dymium59Pr​140.91 Neo­dymium60Nd​144.24 Prome­thium61Pm​ Sama­rium62Sm​150.36 Europ­ium63Eu​151.96 Gadolin­ium64Gd​157.25 Ter­bium65Tb​158.93 Dyspro­sium66Dy​162.50 Hol­mium67Ho​164.93 Erbium68Er​167.26 Thulium69Tm​168.93 Ytter­bium70Yb​173.05   Actin­ium89Ac​ Thor­ium90Th​232.04 Protac­tinium91Pa​231.04 Ura­nium92U​238.03 Neptu­nium93Np​ Pluto­nium94Pu​ Ameri­cium95Am​ Curium96Cm​ Berkel­ium97Bk​ Califor­nium98Cf​ Einstei­nium99Es​ Fer­mium100Fm​ Mende­levium101Md​ Nobel­ium102No​ [Primordial](https://en.wikipedia.org/wiki/Primordial_nuclide) [From decay](https://en.wikipedia.org/wiki/Trace_radioisotope) [Synthetic](https://en.wikipedia.org/wiki/Synthetic_element) **Border** shows natural occurrence of the element [**Standard atomic weight**](https://en.wikipedia.org/wiki/Standard_atomic_weight#Published_values) *A*~r,\ std~(E)[^\[2\]^](https://en.wikipedia.org/wiki/Periodic_table#cite_note-CIAAW2013-3) - Ca: 40.078 --- Abridged value (uncertainty omitted here)[^\[3\]^](https://en.wikipedia.org/wiki/Periodic_table#cite_note-CIAAW2021-4) - Po: \[209\] --- [mass number](https://en.wikipedia.org/wiki/Mass_number) of the most stable isotope -------------------------------------------------- -------------------------------------------------- -------------------------------------------------- -------------------------------------------------- [s-block](https://en.wikipedia.org/wiki/S-block) [f-block](https://en.wikipedia.org/wiki/F-block) [d-block](https://en.wikipedia.org/wiki/D-block) [p-block](https://en.wikipedia.org/wiki/P-block) -------------------------------------------------- -------------------------------------------------- -------------------------------------------------- -------------------------------------------------- A group of blue and yellow circles Description automatically generated3D views of some [hydrogen-like](https://en.wikipedia.org/wiki/Hydrogen-like_atom) atomic orbitals showing probability density and phase (g orbitals and higher are not shown) Each chemical element has a unique [atomic number](https://en.wikipedia.org/wiki/Atomic_number) (*Z*--- for \"Zahl\", German for \"number\") representing the number of [protons](https://en.wikipedia.org/wiki/Proton) in its [nucleus](https://en.wikipedia.org/wiki/Atomic_nucleus).[^\[4\]^](https://en.wikipedia.org/wiki/Periodic_table#cite_note-neutronium-5) Each distinct atomic number therefore corresponds to a class of atom: these classes are called the [chemical elements](https://en.wikipedia.org/wiki/Chemical_element).[^\[5\]^](https://en.wikipedia.org/wiki/Periodic_table#cite_note-6) The chemical elements are what the periodic table classifies and organizes. [Hydrogen](https://en.wikipedia.org/wiki/Hydrogen) is the element with atomic number 1; [helium](https://en.wikipedia.org/wiki/Helium), atomic number 2; [lithium](https://en.wikipedia.org/wiki/Lithium), atomic number 3; and so on. Each of these names can be further abbreviated by a one- or two-letter [chemical symbol](https://en.wikipedia.org/wiki/Chemical_symbol); those for hydrogen, helium, and lithium are respectively H, He, and Li.[^\[6\]^](https://en.wikipedia.org/wiki/Periodic_table#cite_note-IUPAC-redbook-7) Neutrons do not affect the atom\'s chemical identity, but do affect its weight. Atoms with the same number of protons but different numbers of neutrons are called [isotopes](https://en.wikipedia.org/wiki/Isotope) of the same chemical element.[^\[6\]^](https://en.wikipedia.org/wiki/Periodic_table#cite_note-IUPAC-redbook-7) Naturally occurring elements usually occur as mixes of different isotopes; since each isotope usually occurs with a characteristic abundance, naturally occurring elements have well-defined [atomic weights](https://en.wikipedia.org/wiki/Atomic_weight), defined as the average mass of a naturally occurring atom of that element.[^\[7\]^](https://en.wikipedia.org/wiki/Periodic_table#cite_note-ciaaw-8) All elements have multiple [isotopes](https://en.wikipedia.org/wiki/Isotope), variants with the same number of protons but different numbers of [neutrons](https://en.wikipedia.org/wiki/Neutron). For example, [carbon](https://en.wikipedia.org/wiki/Carbon) has three naturally occurring isotopes: all of its [atoms](https://en.wikipedia.org/wiki/Atom) have six protons and most have six neutrons as well, but about one per cent have seven neutrons, and a very small fraction have eight neutrons. Isotopes are never separated in the periodic table; they are always grouped together under a single element. When atomic mass is shown, it is usually the weighted average of naturally occurring isotopes; but if no isotopes occur naturally in significant quantities, the mass of the most stable isotope usually appears, often in parentheses.[^\[8\]^](https://en.wikipedia.org/wiki/Periodic_table#cite_note-Greenwood-9) In the standard periodic table, the elements are listed in order of increasing atomic number. A new row ([*period*](https://en.wikipedia.org/wiki/Period_(periodic_table))) is started when a new [electron shell](https://en.wikipedia.org/wiki/Electron_shell) has its first [electron](https://en.wikipedia.org/wiki/Electron). Columns ([*groups*](https://en.wikipedia.org/wiki/Group_(periodic_table))) are determined by the [electron configuration](https://en.wikipedia.org/wiki/Electron_configuration) of the atom; elements with the same number of electrons in a particular subshell fall into the same columns (e.g. [oxygen](https://en.wikipedia.org/wiki/Oxygen), [sulfur](https://en.wikipedia.org/wiki/Sulfur), and [selenium](https://en.wikipedia.org/wiki/Selenium) are in the same column because they all have four electrons in the outermost p-subshell). Elements with similar chemical properties generally fall into the same group in the periodic table, although in the f-block, and to some respect in the d-block, the elements in the same period tend to have similar properties, as well. Thus, it is relatively easy to predict the chemical properties of an element if one knows the properties of the elements around it.[^\[9\]^](https://en.wikipedia.org/wiki/Periodic_table#cite_note-10) Today, 118 elements are known, the first 94 of which are known to occur naturally on Earth at present.^[\[10\]](https://en.wikipedia.org/wiki/Periodic_table#cite_note-ThorntonBurdette-11)[\[a\]](https://en.wikipedia.org/wiki/Periodic_table#cite_note-transuranium-1)^ The remaining 24, americium to oganesson (95--118), occur only when synthesized in laboratories. Of the 94 naturally occurring elements, 83 are [primordial](https://en.wikipedia.org/wiki/Primordial_element) and 11 occur only in decay chains of primordial elements. A few of the latter are so rare that they were not discovered in nature, but were synthesized in the laboratory before it was determined that they do exist in nature after all: [technetium](https://en.wikipedia.org/wiki/Technetium) (element 43), [promethium](https://en.wikipedia.org/wiki/Promethium) (element 61), [astatine](https://en.wikipedia.org/wiki/Astatine) (element 85), [neptunium](https://en.wikipedia.org/wiki/Neptunium) (element 93), and [plutonium](https://en.wikipedia.org/wiki/Plutonium) (element 94).[^\[12\]^](https://en.wikipedia.org/wiki/Periodic_table#cite_note-emsley-13) No element heavier than [einsteinium](https://en.wikipedia.org/wiki/Einsteinium) (element 99) has ever been observed in macroscopic quantities in its pure form, nor has [astatine](https://en.wikipedia.org/wiki/Astatine); [francium](https://en.wikipedia.org/wiki/Francium) (element 87) has been only photographed in the form of [light](https://en.wikipedia.org/wiki/Light) emitted from microscopic quantities (300,000 atoms).[^\[14\]^](https://en.wikipedia.org/wiki/Periodic_table#cite_note-15) Of the 94 natural elements, eighty have a stable isotope and one more ([bismuth](https://en.wikipedia.org/wiki/Bismuth)) has an almost-stable isotope (with a [half-life](https://en.wikipedia.org/wiki/Half-life) of 2.01×10^19^ years, over a billion times the [age of the universe](https://en.wikipedia.org/wiki/Age_of_the_universe)).^[\[15\]](https://en.wikipedia.org/wiki/Periodic_table#cite_note-Bi209alpha2-16)[\[b\]](https://en.wikipedia.org/wiki/Periodic_table#cite_note-19)^ Two more, [thorium](https://en.wikipedia.org/wiki/Thorium) and [uranium](https://en.wikipedia.org/wiki/Uranium), have isotopes undergoing [radioactive decay](https://en.wikipedia.org/wiki/Radioactive_decay) with a half-life comparable to the [age of the Earth](https://en.wikipedia.org/wiki/Age_of_the_Earth). The stable elements plus bismuth, thorium, and uranium make up the 83 [primordial](https://en.wikipedia.org/wiki/Primordial_nuclide) elements that survived from the Earth\'s formation.[^\[c\]^](https://en.wikipedia.org/wiki/Periodic_table#cite_note-23) The remaining eleven natural elements decay quickly enough that their continued trace occurrence rests primarily on being constantly regenerated as intermediate products of the decay of thorium and uranium.[^\[d\]^](https://en.wikipedia.org/wiki/Periodic_table#cite_note-25) All 24 known artificial elements are radioactive.[^\[6\]^](https://en.wikipedia.org/wiki/Periodic_table#cite_note-IUPAC-redbook-7) **Group names and numbers** Under an international naming convention, the groups are numbered numerically from 1 to 18 from the leftmost column (the alkali metals) to the rightmost column (the noble gases). The f-block groups are ignored in this numbering.[^\[22\]^](https://en.wikipedia.org/wiki/Periodic_table#cite_note-IUPAC-26) Groups can also be named by their first element, e.g. the \"scandium group\" for group 3.[^\[22\]^](https://en.wikipedia.org/wiki/Periodic_table#cite_note-IUPAC-26) Previously, groups were known by [Roman numerals](https://en.wikipedia.org/wiki/Roman_numerals). In the [United States](https://en.wikipedia.org/wiki/United_States), the Roman numerals were followed by either an \"A\" if the group was in the [s-](https://en.wikipedia.org/wiki/S-block) or [p-block](https://en.wikipedia.org/wiki/P-block), or a \"B\" if the group was in the [d-block](https://en.wikipedia.org/wiki/D-block). The Roman numerals used correspond to the last digit of today\'s naming convention (e.g. the [group 4 elements](https://en.wikipedia.org/wiki/Group_4_element) were group IVB, and the [group 14 elements](https://en.wikipedia.org/wiki/Carbon_group) were group IVA). In [Europe](https://en.wikipedia.org/wiki/Europe), the lettering was similar, except that \"A\" was used for groups 1 through 7, and \"B\" was used for groups 11 through 17. In addition, groups 8, 9 and 10 used to be treated as one triple-sized group, known collectively in both notations as group VIII. In 1988, the new [IUPAC](https://en.wikipedia.org/wiki/IUPAC) (International Union of Pure and Applied Chemistry) naming system (1--18) was put into use, and the old group names (I--VIII) were deprecated.[^\[23\]^](https://en.wikipedia.org/wiki/Periodic_table#cite_note-Fluck-27) hide - [v](https://en.wikipedia.org/wiki/Template:Periodic_table_(group_names)) - [t](https://en.wikipedia.org/wiki/Template_talk:Periodic_table_(group_names)) - [e](https://en.wikipedia.org/wiki/Special:EditPage/Template:Periodic_table_(group_names)) **Groups in the periodic table** [IUPAC group](https://en.wikipedia.org/wiki/Group_(periodic_table)) **(https://en.wikipedia.org/wiki/Group_1_element)[^a^](https://en.wikipedia.org/wiki/Periodic_table#endnote_group1)** [**2**](https://en.wikipedia.org/wiki/Alkaline_earth_metal) **---[^b^](https://en.wikipedia.org/wiki/Periodic_table#endnote_f-block_groups)** **(https://en.wikipedia.org/wiki/Group_3_element)[^c^](https://en.wikipedia.org/wiki/Periodic_table#endnote_ScYLu)** [**4**](https://en.wikipedia.org/wiki/Group_4_element) [**5**](https://en.wikipedia.org/wiki/Group_5_element) [**6**](https://en.wikipedia.org/wiki/Group_6_element) [**7**](https://en.wikipedia.org/wiki/Group_7_element) [**8**](https://en.wikipedia.org/wiki/Group_8_element) [**9**](https://en.wikipedia.org/wiki/Group_9_element) [**10**](https://en.wikipedia.org/wiki/Group_10_element) [**11**](https://en.wikipedia.org/wiki/Group_11_element) [**12**](https://en.wikipedia.org/wiki/Group_12_element) [**13**](https://en.wikipedia.org/wiki/Boron_group) [**14**](https://en.wikipedia.org/wiki/Carbon_group) [**15**](https://en.wikipedia.org/wiki/Pnictogen) [**16**](https://en.wikipedia.org/wiki/Chalcogen) [**17**](https://en.wikipedia.org/wiki/Halogen) [**18**](https://en.wikipedia.org/wiki/Noble_gas) ----------------------------------------------------------------------------------------------------------------------------- -------------------------------------------------------------------------------------------------------------------------- ----------------------------------------------------------------------------- ----------------------------------------------------------------------------------- ------------------------------------------------------------------------------------------------------------------------- -------------------------------------------------------- -------------------------------------------------------- -------------------------------------------------------- -------------------------------------------------------- -------------------------------------------------------- -------------------------------------------------------- ---------------------------------------------------------- ---------------------------------------------------------- ---------------------------------------------------------- ----------------------------------------------------- ------------------------------------------------------- --------------------------------------------------------- -------------------------------------------------------------------- ----------------------------------------------------- ---------------------------------------------------------- [Mendeleev](https://en.wikipedia.org/wiki/Dmitri_Mendeleev#Periodic_table) (I--VIII) I II III IV V VI VII VIII I II III IV V VI VII [^d^](https://en.wikipedia.org/wiki/Periodic_table#endnote_group0) [CAS](https://en.wikipedia.org/wiki/Group_(periodic_table)#CAS_and_old_IUPAC) (US, A-B-A) IA IIA IIIB IVB VB VIB VIIB VIIIB IB IIB IIIA IVA VA VIA VIIA VIIIA [Old IUPAC](https://en.wikipedia.org/wiki/Group_(periodic_table)#CAS_and_old_IUPAC) (Europe, A-B) IA IIA IIIA IVA VA VIA VIIA VIII IB IIB IIIB IVB VB VIB VIIB 0 [Trivial name](https://en.wikipedia.org/wiki/Trivial_name)[^r^](https://en.wikipedia.org/wiki/Periodic_table#endnote_IUPAC) H and [alkali metals](https://en.wikipedia.org/wiki/Alkali_metal) [alkaline earth metals](https://en.wikipedia.org/wiki/Alkaline_earth_metal) [triels](https://en.wikipedia.org/wiki/Boron_group) [tetrels](https://en.wikipedia.org/wiki/Carbon_group) [pnicto­gens](https://en.wikipedia.org/wiki/Pnictogens) [chal­co­gens](https://en.wikipedia.org/wiki/Chalcogens) [halo­gens](https://en.wikipedia.org/wiki/Halogens) [noble gases](https://en.wikipedia.org/wiki/Noble_gases) Name by element[^r^](https://en.wikipedia.org/wiki/Periodic_table#endnote_IUPAC) lith­ium group beryl­lium group scan­dium group titan­ium group vana­dium group chro­mium group man­ga­nese group iron group co­balt group nickel group cop­per group zinc group boron group car­bon group nitro­gen group oxy­gen group fluor­ine group helium *or* neon group [Period 1](https://en.wikipedia.org/wiki/Period_1_element) [ H ](https://en.wikipedia.org/wiki/Hydrogen) [He](https://en.wikipedia.org/wiki/Helium) [Period 2](https://en.wikipedia.org/wiki/Period_2_element) [Li](https://en.wikipedia.org/wiki/Lithium) [Be](https://en.wikipedia.org/wiki/Beryllium) [B](https://en.wikipedia.org/wiki/Boron) [C](https://en.wikipedia.org/wiki/Carbon) [N](https://en.wikipedia.org/wiki/Nitrogen) [O](https://en.wikipedia.org/wiki/Oxygen) [F](https://en.wikipedia.org/wiki/Fluorine) [Ne](https://en.wikipedia.org/wiki/Neon) [Period 3](https://en.wikipedia.org/wiki/Period_3_element) [Na](https://en.wikipedia.org/wiki/Sodium) [Mg](https://en.wikipedia.org/wiki/Magnesium) [Al](https://en.wikipedia.org/wiki/Aluminium) [Si](https://en.wikipedia.org/wiki/Silicon) [P](https://en.wikipedia.org/wiki/Phosphorus) [S](https://en.wikipedia.org/wiki/Sulfur) [Cl](https://en.wikipedia.org/wiki/Chlorine) [Ar](https://en.wikipedia.org/wiki/Argon) [Period 4](https://en.wikipedia.org/wiki/Period_4_element) [K](https://en.wikipedia.org/wiki/Potassium) [Ca](https://en.wikipedia.org/wiki/Calcium) [Sc](https://en.wikipedia.org/wiki/Scandium) [Ti](https://en.wikipedia.org/wiki/Titanium) [V](https://en.wikipedia.org/wiki/Vanadium) [Cr](https://en.wikipedia.org/wiki/Chromium) [Mn](https://en.wikipedia.org/wiki/Manganese) [Fe](https://en.wikipedia.org/wiki/Iron) [Co](https://en.wikipedia.org/wiki/Cobalt) [Ni](https://en.wikipedia.org/wiki/Nickel) [Cu](https://en.wikipedia.org/wiki/Copper) [Zn](https://en.wikipedia.org/wiki/Zinc) [Ga](https://en.wikipedia.org/wiki/Gallium) [Ge](https://en.wikipedia.org/wiki/Germanium) [As](https://en.wikipedia.org/wiki/Arsenic) [Se](https://en.wikipedia.org/wiki/Selenium) [Br](https://en.wikipedia.org/wiki/Bromine) [Kr](https://en.wikipedia.org/wiki/Krypton) [Period 5](https://en.wikipedia.org/wiki/Period_5_element) [Rb](https://en.wikipedia.org/wiki/Rubidium) [Sr](https://en.wikipedia.org/wiki/Strontium) [Y](https://en.wikipedia.org/wiki/Yttrium) [Zr](https://en.wikipedia.org/wiki/Zirconium) [Nb](https://en.wikipedia.org/wiki/Niobium) [Mo](https://en.wikipedia.org/wiki/Molybdenum) [Tc](https://en.wikipedia.org/wiki/Technetium) [Ru](https://en.wikipedia.org/wiki/Ruthenium) [Rh](https://en.wikipedia.org/wiki/Rhodium) [Pd](https://en.wikipedia.org/wiki/Palladium) [Ag](https://en.wikipedia.org/wiki/Silver) [Cd](https://en.wikipedia.org/wiki/Cadmium) [In](https://en.wikipedia.org/wiki/Indium) [Sn](https://en.wikipedia.org/wiki/Tin) [Sb](https://en.wikipedia.org/wiki/Antimony) [Te](https://en.wikipedia.org/wiki/Tellurium) [I](https://en.wikipedia.org/wiki/Iodine) [Xe](https://en.wikipedia.org/wiki/Xenon) [Period 6](https://en.wikipedia.org/wiki/Period_6_element) [Cs](https://en.wikipedia.org/wiki/Caesium) [Ba](https://en.wikipedia.org/wiki/Barium) [La--Yb](https://en.wikipedia.org/wiki/Lanthanide) [Lu](https://en.wikipedia.org/wiki/Lutetium) [Hf](https://en.wikipedia.org/wiki/Hafnium) [Ta](https://en.wikipedia.org/wiki/Tantalum) [W](https://en.wikipedia.org/wiki/Tungsten) [Re](https://en.wikipedia.org/wiki/Rhenium) [Os](https://en.wikipedia.org/wiki/Osmium) [Ir](https://en.wikipedia.org/wiki/Iridium) [Pt](https://en.wikipedia.org/wiki/Platinum) [Au](https://en.wikipedia.org/wiki/Gold) [Hg](https://en.wikipedia.org/wiki/Mercury_(element)) [Tl](https://en.wikipedia.org/wiki/Thallium) [Pb](https://en.wikipedia.org/wiki/Lead) [Bi](https://en.wikipedia.org/wiki/Bismuth) [Po](https://en.wikipedia.org/wiki/Polonium) [At](https://en.wikipedia.org/wiki/Astatine) [Rn](https://en.wikipedia.org/wiki/Radon) [Period 7](https://en.wikipedia.org/wiki/Period_7_element) [Fr](https://en.wikipedia.org/wiki/Francium) [Ra](https://en.wikipedia.org/wiki/Radium) [Ac--No](https://en.wikipedia.org/wiki/Actinide) [Lr](https://en.wikipedia.org/wiki/Lawrencium) [Rf](https://en.wikipedia.org/wiki/Rutherfordium) [Db](https://en.wikipedia.org/wiki/Dubnium) [Sg](https://en.wikipedia.org/wiki/Seaborgium) [Bh](https://en.wikipedia.org/wiki/Bohrium) [Hs](https://en.wikipedia.org/wiki/Hassium) [Mt](https://en.wikipedia.org/wiki/Meitnerium) [Ds](https://en.wikipedia.org/wiki/Darmstadtium) [Rg](https://en.wikipedia.org/wiki/Roentgenium) [Cn](https://en.wikipedia.org/wiki/Copernicium) [Nh](https://en.wikipedia.org/wiki/Nihonium) [Fl](https://en.wikipedia.org/wiki/Flerovium) [Mc](https://en.wikipedia.org/wiki/Moscovium) [Lv](https://en.wikipedia.org/wiki/Livermorium) [Ts](https://en.wikipedia.org/wiki/Tennessine) [Og](https://en.wikipedia.org/wiki/Oganesson) ^a^ Group 1 is composed of hydrogen (H) and the alkali metals. Elements of the group have one s-electron in the outer electron shell. Hydrogen is not considered to be an alkali metal as it is not a metal, though it is more analogous to them than any other group. This makes the group somewhat exceptional.\ ^b^ The 14 [f-block groups](https://en.wikipedia.org/wiki/F-block_groups) (columns) do not have a group number.\ ^c^ The correct composition of group 3 is scandium (Sc), yttrium (Y), lutetium (Lu), and lawrencium (Lr), as shown here: this is endorsed by 1988[^\[23\]^](https://en.wikipedia.org/wiki/Periodic_table#cite_note-Fluck-27) and 2021[^\[24\]^](https://en.wikipedia.org/wiki/Periodic_table#cite_note-2021IUPAC-28) IUPAC reports on the question. General inorganic chemistry texts often put scandium (Sc), yttrium (Y), lanthanum (La), and actinium (Ac) in group 3, so that Ce--Lu and Th--Lr become the f-block between groups 3 and 4; this was based on incorrectly measured electron configurations from history,[^\[25\]^](https://en.wikipedia.org/wiki/Periodic_table#cite_note-Jensen1982-29) and [Lev Landau](https://en.wikipedia.org/wiki/Lev_Landau) and [Evgeny Lifshitz](https://en.wikipedia.org/wiki/Evgeny_Lifshitz) already considered it incorrect in 1948.[^\[26\]^](https://en.wikipedia.org/wiki/Periodic_table#cite_note-Landau-30) Arguments can still occasionally be encountered in the contemporary literature purporting to defend it, but most authors consider them logically inconsistent.^[\[27\]](https://en.wikipedia.org/wiki/Periodic_table#cite_note-Jensen2015-31)[\[28\]](https://en.wikipedia.org/wiki/Periodic_table#cite_note-Scerri2009-32)[\[29\]](https://en.wikipedia.org/wiki/Periodic_table#cite_note-Chemey-33)^ Some sources follow a compromise that puts La--Lu and Ac--Lr as the f-block rows (despite that giving 15 f-block elements in each row, which contradicts quantum mechanics), leaving the heavier members of group 3 ambiguous.[^\[24\]^](https://en.wikipedia.org/wiki/Periodic_table#cite_note-2021IUPAC-28) See also [Group 3 element\#Composition](https://en.wikipedia.org/wiki/Group_3_element#Composition).\ ^d^ Group 18, the noble gases, were not discovered at the time of Mendeleev\'s original table. Later (1902), Mendeleev accepted the evidence for their existence, and they could be placed in a new \"group 0\", consistently and without breaking the periodic table principle.\ ^r^ Group name as recommended by IUPAC. **Presentation forms** [Hydrogen](https://en.wikipedia.org/wiki/Hydrogen) [Helium](https://en.wikipedia.org/wiki/Helium) ------------------------------------------------------ ------------------------------------------------------ ------------------------------------------------------ ------------------------------------------------------ ------------------------------------------------------------ -------------------------------------------------------- -------------------------------------------------------- -------------------------------------------------------- -------------------------------------------------------- -------------------------------------------------------- ------------------------------------------------------ ---------------------------------------------------------- ---------------------------------------------------------- -------------------------------------------------- ---------------------------------------------------------- ------------------------------------------------------ -------------------------------------------------------- -------------------------------------------------------------- ---------------------------------------------------- -------------------------------------------------------- -------------------------------------------------- -------------------------------------------------- -------------------------------------------------------- ------------------------------------------------------------ ---------------------------------------------------------- ---------------------------------------------------------------------- ---------------------------------------------------- ------------------------------------------------------ ------------------------------------------------------ ---------------------------------------------------------- -------------------------------------------------------- ------------------------------------------------------ [Lithium](https://en.wikipedia.org/wiki/Lithium) [Beryllium](https://en.wikipedia.org/wiki/Beryllium) [Boron](https://en.wikipedia.org/wiki/Boron) [Carbon](https://en.wikipedia.org/wiki/Carbon) [Nitrogen](https://en.wikipedia.org/wiki/Nitrogen) [Oxygen](https://en.wikipedia.org/wiki/Oxygen) [Fluorine](https://en.wikipedia.org/wiki/Fluorine) [Neon](https://en.wikipedia.org/wiki/Neon) [Sodium](https://en.wikipedia.org/wiki/Sodium) [Magnesium](https://en.wikipedia.org/wiki/Magnesium) [Aluminium](https://en.wikipedia.org/wiki/Aluminium) [Silicon](https://en.wikipedia.org/wiki/Silicon) [Phosphorus](https://en.wikipedia.org/wiki/Phosphorus) [Sulfur](https://en.wikipedia.org/wiki/Sulfur) [Chlorine](https://en.wikipedia.org/wiki/Chlorine) [Argon](https://en.wikipedia.org/wiki/Argon) [Potassium](https://en.wikipedia.org/wiki/Potassium) [Calcium](https://en.wikipedia.org/wiki/Calcium) [Scandium](https://en.wikipedia.org/wiki/Scandium) [Titanium](https://en.wikipedia.org/wiki/Titanium) [Vanadium](https://en.wikipedia.org/wiki/Vanadium) [Chromium](https://en.wikipedia.org/wiki/Chromium) [Manganese](https://en.wikipedia.org/wiki/Manganese) [Iron](https://en.wikipedia.org/wiki/Iron) [Cobalt](https://en.wikipedia.org/wiki/Cobalt) [Nickel](https://en.wikipedia.org/wiki/Nickel) [Copper](https://en.wikipedia.org/wiki/Copper) [Zinc](https://en.wikipedia.org/wiki/Zinc) [Gallium](https://en.wikipedia.org/wiki/Gallium) [Germanium](https://en.wikipedia.org/wiki/Germanium) [Arsenic](https://en.wikipedia.org/wiki/Arsenic) [Selenium](https://en.wikipedia.org/wiki/Selenium) [Bromine](https://en.wikipedia.org/wiki/Bromine) [Krypton](https://en.wikipedia.org/wiki/Krypton) [Rubidium](https://en.wikipedia.org/wiki/Rubidium) [Strontium](https://en.wikipedia.org/wiki/Strontium) [Yttrium](https://en.wikipedia.org/wiki/Yttrium) [Zirconium](https://en.wikipedia.org/wiki/Zirconium) [Niobium](https://en.wikipedia.org/wiki/Niobium) [Molybdenum](https://en.wikipedia.org/wiki/Molybdenum) [Technetium](https://en.wikipedia.org/wiki/Technetium) [Ruthenium](https://en.wikipedia.org/wiki/Ruthenium) [Rhodium](https://en.wikipedia.org/wiki/Rhodium) [Palladium](https://en.wikipedia.org/wiki/Palladium) [Silver](https://en.wikipedia.org/wiki/Silver) [Cadmium](https://en.wikipedia.org/wiki/Cadmium) [Indium](https://en.wikipedia.org/wiki/Indium) [Tin](https://en.wikipedia.org/wiki/Tin) [Antimony](https://en.wikipedia.org/wiki/Antimony) [Tellurium](https://en.wikipedia.org/wiki/Tellurium) [Iodine](https://en.wikipedia.org/wiki/Iodine) [Xenon](https://en.wikipedia.org/wiki/Xenon) [Caesium](https://en.wikipedia.org/wiki/Caesium) [Barium](https://en.wikipedia.org/wiki/Barium) [Lanthanum](https://en.wikipedia.org/wiki/Lanthanum) [Cerium](https://en.wikipedia.org/wiki/Cerium) [Praseodymium](https://en.wikipedia.org/wiki/Praseodymium) [Neodymium](https://en.wikipedia.org/wiki/Neodymium) [Promethium](https://en.wikipedia.org/wiki/Promethium) [Samarium](https://en.wikipedia.org/wiki/Samarium) [Europium](https://en.wikipedia.org/wiki/Europium) [Gadolinium](https://en.wikipedia.org/wiki/Gadolinium) [Terbium](https://en.wikipedia.org/wiki/Terbium) [Dysprosium](https://en.wikipedia.org/wiki/Dysprosium) [Holmium](https://en.wikipedia.org/wiki/Holmium) [Erbium](https://en.wikipedia.org/wiki/Erbium) [Thulium](https://en.wikipedia.org/wiki/Thulium) [Ytterbium](https://en.wikipedia.org/wiki/Ytterbium) [Lutetium](https://en.wikipedia.org/wiki/Lutetium) [Hafnium](https://en.wikipedia.org/wiki/Hafnium) [Tantalum](https://en.wikipedia.org/wiki/Tantalum) [Tungsten](https://en.wikipedia.org/wiki/Tungsten) [Rhenium](https://en.wikipedia.org/wiki/Rhenium) [Osmium](https://en.wikipedia.org/wiki/Osmium) [Iridium](https://en.wikipedia.org/wiki/Iridium) [Platinum](https://en.wikipedia.org/wiki/Platinum) [Gold](https://en.wikipedia.org/wiki/Gold) [Mercury (element)](https://en.wikipedia.org/wiki/Mercury_(element)) [Thallium](https://en.wikipedia.org/wiki/Thallium) [Lead](https://en.wikipedia.org/wiki/Lead) [Bismuth](https://en.wikipedia.org/wiki/Bismuth) [Polonium](https://en.wikipedia.org/wiki/Polonium) [Astatine](https://en.wikipedia.org/wiki/Astatine) [Radon](https://en.wikipedia.org/wiki/Radon) [Francium](https://en.wikipedia.org/wiki/Francium) [Radium](https://en.wikipedia.org/wiki/Radium) [Actinium](https://en.wikipedia.org/wiki/Actinium) [Thorium](https://en.wikipedia.org/wiki/Thorium) [Protactinium](https://en.wikipedia.org/wiki/Protactinium) [Uranium](https://en.wikipedia.org/wiki/Uranium) [Neptunium](https://en.wikipedia.org/wiki/Neptunium) [Plutonium](https://en.wikipedia.org/wiki/Plutonium) [Americium](https://en.wikipedia.org/wiki/Americium) [Curium](https://en.wikipedia.org/wiki/Curium) [Berkelium](https://en.wikipedia.org/wiki/Berkelium) [Californium](https://en.wikipedia.org/wiki/Californium) [Einsteinium](https://en.wikipedia.org/wiki/Einsteinium) [Fermium](https://en.wikipedia.org/wiki/Fermium) [Mendelevium](https://en.wikipedia.org/wiki/Mendelevium) [Nobelium](https://en.wikipedia.org/wiki/Nobelium) [Lawrencium](https://en.wikipedia.org/wiki/Lawrencium) [Rutherfordium](https://en.wikipedia.org/wiki/Rutherfordium) [Dubnium](https://en.wikipedia.org/wiki/Dubnium) [Seaborgium](https://en.wikipedia.org/wiki/Seaborgium) [Bohrium](https://en.wikipedia.org/wiki/Bohrium) [Hassium](https://en.wikipedia.org/wiki/Hassium) [Meitnerium](https://en.wikipedia.org/wiki/Meitnerium) [Darmstadtium](https://en.wikipedia.org/wiki/Darmstadtium) [Roentgenium](https://en.wikipedia.org/wiki/Roentgenium) [Copernicium](https://en.wikipedia.org/wiki/Copernicium) [Nihonium](https://en.wikipedia.org/wiki/Nihonium) [Flerovium](https://en.wikipedia.org/wiki/Flerovium) [Moscovium](https://en.wikipedia.org/wiki/Moscovium) [Livermorium](https://en.wikipedia.org/wiki/Livermorium) [Tennessine](https://en.wikipedia.org/wiki/Tennessine) [Oganesson](https://en.wikipedia.org/wiki/Oganesson) 32 columns [Hydrogen](https://en.wikipedia.org/wiki/Hydrogen) [Helium](https://en.wikipedia.org/wiki/Helium) ------------------------------------------------------ ------------------------------------------------------ ------------------------------------------------------ -------------------------------------------------------- -------------------------------------------------------------- -------------------------------------------------------- -------------------------------------------------------- -------------------------------------------------------- ------------------------------------------------------ -------------------------------------------------------- ------------------------------------------------------------ ---------------------------------------------------------- ---------------------------------------------------------------------- ---------------------------------------------------- ---------------------------------------------------------- ------------------------------------------------------ ---------------------------------------------------------- -------------------------------------------------------- ------------------------------------------------------ [Lithium](https://en.wikipedia.org/wiki/Lithium) [Beryllium](https://en.wikipedia.org/wiki/Beryllium) [Boron](https://en.wikipedia.org/wiki/Boron) [Carbon](https://en.wikipedia.org/wiki/Carbon) [Nitrogen](https://en.wikipedia.org/wiki/Nitrogen) [Oxygen](https://en.wikipedia.org/wiki/Oxygen) [Fluorine](https://en.wikipedia.org/wiki/Fluorine) [Neon](https://en.wikipedia.org/wiki/Neon) [Sodium](https://en.wikipedia.org/wiki/Sodium) [Magnesium](https://en.wikipedia.org/wiki/Magnesium) [Aluminium](https://en.wikipedia.org/wiki/Aluminium) [Silicon](https://en.wikipedia.org/wiki/Silicon) [Phosphorus](https://en.wikipedia.org/wiki/Phosphorus) [Sulfur](https://en.wikipedia.org/wiki/Sulfur) [Chlorine](https://en.wikipedia.org/wiki/Chlorine) [Argon](https://en.wikipedia.org/wiki/Argon) [Potassium](https://en.wikipedia.org/wiki/Potassium) [Calcium](https://en.wikipedia.org/wiki/Calcium) [Scandium](https://en.wikipedia.org/wiki/Scandium) [Titanium](https://en.wikipedia.org/wiki/Titanium) [Vanadium](https://en.wikipedia.org/wiki/Vanadium) [Chromium](https://en.wikipedia.org/wiki/Chromium) [Manganese](https://en.wikipedia.org/wiki/Manganese) [Iron](https://en.wikipedia.org/wiki/Iron) [Cobalt](https://en.wikipedia.org/wiki/Cobalt) [Nickel](https://en.wikipedia.org/wiki/Nickel) [Copper](https://en.wikipedia.org/wiki/Copper) [Zinc](https://en.wikipedia.org/wiki/Zinc) [Gallium](https://en.wikipedia.org/wiki/Gallium) [Germanium](https://en.wikipedia.org/wiki/Germanium) [Arsenic](https://en.wikipedia.org/wiki/Arsenic) [Selenium](https://en.wikipedia.org/wiki/Selenium) [Bromine](https://en.wikipedia.org/wiki/Bromine) [Krypton](https://en.wikipedia.org/wiki/Krypton) [Rubidium](https://en.wikipedia.org/wiki/Rubidium) [Strontium](https://en.wikipedia.org/wiki/Strontium) [Yttrium](https://en.wikipedia.org/wiki/Yttrium) [Zirconium](https://en.wikipedia.org/wiki/Zirconium) [Niobium](https://en.wikipedia.org/wiki/Niobium) [Molybdenum](https://en.wikipedia.org/wiki/Molybdenum) [Technetium](https://en.wikipedia.org/wiki/Technetium) [Ruthenium](https://en.wikipedia.org/wiki/Ruthenium) [Rhodium](https://en.wikipedia.org/wiki/Rhodium) [Palladium](https://en.wikipedia.org/wiki/Palladium) [Silver](https://en.wikipedia.org/wiki/Silver) [Cadmium](https://en.wikipedia.org/wiki/Cadmium) [Indium](https://en.wikipedia.org/wiki/Indium) [Tin](https://en.wikipedia.org/wiki/Tin) [Antimony](https://en.wikipedia.org/wiki/Antimony) [Tellurium](https://en.wikipedia.org/wiki/Tellurium) [Iodine](https://en.wikipedia.org/wiki/Iodine) [Xenon](https://en.wikipedia.org/wiki/Xenon) [Caesium](https://en.wikipedia.org/wiki/Caesium) [Barium](https://en.wikipedia.org/wiki/Barium) [Lutetium](https://en.wikipedia.org/wiki/Lutetium) [Hafnium](https://en.wikipedia.org/wiki/Hafnium) [Tantalum](https://en.wikipedia.org/wiki/Tantalum) [Tungsten](https://en.wikipedia.org/wiki/Tungsten) [Rhenium](https://en.wikipedia.org/wiki/Rhenium) [Osmium](https://en.wikipedia.org/wiki/Osmium) [Iridium](https://en.wikipedia.org/wiki/Iridium) [Platinum](https://en.wikipedia.org/wiki/Platinum) [Gold](https://en.wikipedia.org/wiki/Gold) [Mercury (element)](https://en.wikipedia.org/wiki/Mercury_(element)) [Thallium](https://en.wikipedia.org/wiki/Thallium) [Lead](https://en.wikipedia.org/wiki/Lead) [Bismuth](https://en.wikipedia.org/wiki/Bismuth) [Polonium](https://en.wikipedia.org/wiki/Polonium) [Astatine](https://en.wikipedia.org/wiki/Astatine) [Radon](https://en.wikipedia.org/wiki/Radon) [Francium](https://en.wikipedia.org/wiki/Francium) [Radium](https://en.wikipedia.org/wiki/Radium) [Lawrencium](https://en.wikipedia.org/wiki/Lawrencium) [Rutherfordium](https://en.wikipedia.org/wiki/Rutherfordium) [Dubnium](https://en.wikipedia.org/wiki/Dubnium) [Seaborgium](https://en.wikipedia.org/wiki/Seaborgium) [Bohrium](https://en.wikipedia.org/wiki/Bohrium) [Hassium](https://en.wikipedia.org/wiki/Hassium) [Meitnerium](https://en.wikipedia.org/wiki/Meitnerium) [Darmstadtium](https://en.wikipedia.org/wiki/Darmstadtium) [Roentgenium](https://en.wikipedia.org/wiki/Roentgenium) [Copernicium](https://en.wikipedia.org/wiki/Copernicium) [Nihonium](https://en.wikipedia.org/wiki/Nihonium) [Flerovium](https://en.wikipedia.org/wiki/Flerovium) [Moscovium](https://en.wikipedia.org/wiki/Moscovium) [Livermorium](https://en.wikipedia.org/wiki/Livermorium) [Tennessine](https://en.wikipedia.org/wiki/Tennessine) [Oganesson](https://en.wikipedia.org/wiki/Oganesson) ​ [Lanthanum](https://en.wikipedia.org/wiki/Lanthanum) [Cerium](https://en.wikipedia.org/wiki/Cerium) [Praseodymium](https://en.wikipedia.org/wiki/Praseodymium) [Neodymium](https://en.wikipedia.org/wiki/Neodymium) [Promethium](https://en.wikipedia.org/wiki/Promethium) [Samarium](https://en.wikipedia.org/wiki/Samarium) [Europium](https://en.wikipedia.org/wiki/Europium) [Gadolinium](https://en.wikipedia.org/wiki/Gadolinium) [Terbium](https://en.wikipedia.org/wiki/Terbium) [Dysprosium](https://en.wikipedia.org/wiki/Dysprosium) [Holmium](https://en.wikipedia.org/wiki/Holmium) [Erbium](https://en.wikipedia.org/wiki/Erbium) [Thulium](https://en.wikipedia.org/wiki/Thulium) [Ytterbium](https://en.wikipedia.org/wiki/Ytterbium) [Actinium](https://en.wikipedia.org/wiki/Actinium) [Thorium](https://en.wikipedia.org/wiki/Thorium) [Protactinium](https://en.wikipedia.org/wiki/Protactinium) [Uranium](https://en.wikipedia.org/wiki/Uranium) [Neptunium](https://en.wikipedia.org/wiki/Neptunium) [Plutonium](https://en.wikipedia.org/wiki/Plutonium) [Americium](https://en.wikipedia.org/wiki/Americium) [Curium](https://en.wikipedia.org/wiki/Curium) [Berkelium](https://en.wikipedia.org/wiki/Berkelium) [Californium](https://en.wikipedia.org/wiki/Californium) [Einsteinium](https://en.wikipedia.org/wiki/Einsteinium) [Fermium](https://en.wikipedia.org/wiki/Fermium) [Mendelevium](https://en.wikipedia.org/wiki/Mendelevium) [Nobelium](https://en.wikipedia.org/wiki/Nobelium) 18 columns For reasons of space,^[\[30\]](https://en.wikipedia.org/wiki/Periodic_table#cite_note-Petrucci331-34)[\[31\]](https://en.wikipedia.org/wiki/Periodic_table#cite_note-35)^ the periodic table is commonly presented with the f-block elements cut out and positioned as a distinct part below the main body.^[\[32\]](https://en.wikipedia.org/wiki/Periodic_table#cite_note-cartoon-36)[\[30\]](https://en.wikipedia.org/wiki/Periodic_table#cite_note-Petrucci331-34)[\[23\]](https://en.wikipedia.org/wiki/Periodic_table#cite_note-Fluck-27)^ This reduces the number of element columns from 32 to 18.[^\[30\]^](https://en.wikipedia.org/wiki/Periodic_table#cite_note-Petrucci331-34) Both forms represent the same periodic table.[^\[6\]^](https://en.wikipedia.org/wiki/Periodic_table#cite_note-IUPAC-redbook-7) The form with the f-block included in the main body is sometimes called the 32-column[^\[6\]^](https://en.wikipedia.org/wiki/Periodic_table#cite_note-IUPAC-redbook-7) or long form;[^\[33\]^](https://en.wikipedia.org/wiki/Periodic_table#cite_note-Thyssen-37) the form with the f-block cut out the 18-column[^\[6\]^](https://en.wikipedia.org/wiki/Periodic_table#cite_note-IUPAC-redbook-7) or medium-long form.[^\[33\]^](https://en.wikipedia.org/wiki/Periodic_table#cite_note-Thyssen-37) The 32-column form has the advantage of showing all elements in their correct sequence, but it has the disadvantage of requiring more space.[^\[34\]^](https://en.wikipedia.org/wiki/Periodic_table#cite_note-38) The form chosen is an editorial choice, and does not imply any change of scientific claim or statement. For example, when discussing [the composition of group 3](https://en.wikipedia.org/wiki/Group_3_element#Composition), the options can be shown equally (unprejudiced) in both forms.[^\[35\]^](https://en.wikipedia.org/wiki/Periodic_table#cite_note-2015IUPAC-39) Periodic tables usually at least show the elements\' symbols; many also provide supplementary information about the elements, either via colour-coding or as data in the cells. The above table shows the names and atomic numbers of the elements, and also their blocks, natural occurrences and [standard atomic weights](https://en.wikipedia.org/wiki/Standard_atomic_weight). For the short-lived elements without standard atomic weights, the mass number of the most stable known isotope is used instead. Other tables may include properties such as state of matter, melting and boiling points, densities, as well as provide different classifications of the elements.[^\[e\]^](https://en.wikipedia.org/wiki/Periodic_table#cite_note-40) **Electron configurations** *Main article: [Electron configuration](https://en.wikipedia.org/wiki/Electron_configuration)* The periodic table is a graphic description of the periodic law,[^\[36\]^](https://en.wikipedia.org/wiki/Periodic_table#cite_note-Scerri17-41) which states that the properties and atomic structures of the chemical elements are a [periodic function](https://en.wikipedia.org/wiki/Periodic_function) of their [atomic number](https://en.wikipedia.org/wiki/Atomic_number).[^\[37\]^](https://en.wikipedia.org/wiki/Periodic_table#cite_note-42) Elements are placed in the periodic table according to their [electron configurations](https://en.wikipedia.org/wiki/Electron_configuration),[^\[38\]^](https://en.wikipedia.org/wiki/Periodic_table#cite_note-Jensen2009-43) the periodic recurrences of which explain the [trends](https://en.wikipedia.org/wiki/Periodic_trends) in properties across the periodic table.[^\[39\]^](https://en.wikipedia.org/wiki/Periodic_table#cite_note-FIII19-44) An electron can be thought of as inhabiting an [atomic orbital](https://en.wikipedia.org/wiki/Atomic_orbital), which characterizes the probability it can be found in any particular region around the atom. Their energies are quantised, which is to say that they can only take discrete values. Furthermore, electrons obey the [Pauli exclusion principle](https://en.wikipedia.org/wiki/Pauli_exclusion_principle): different electrons must always be in different states. This allows classification of the possible states an electron can take in various energy levels known as shells, divided into individual subshells, which each contain one or more orbitals. Each orbital can contain up to two electrons: they are distinguished by a quantity known as [spin](https://en.wikipedia.org/wiki/Spin_(physics)), conventionally labelled \"up\" or \"down\".^[\[40\]](https://en.wikipedia.org/wiki/Periodic_table#cite_note-45)[\[f\]](https://en.wikipedia.org/wiki/Periodic_table#cite_note-47)^ In a cold atom (one in its ground state), electrons arrange themselves in such a way that the total energy they have is minimized by occupying the lowest-energy orbitals available.[^\[42\]^](https://en.wikipedia.org/wiki/Periodic_table#cite_note-48) Only the outermost electrons (so-called [valence electrons](https://en.wikipedia.org/wiki/Valence_electron)) have enough energy to break free of the nucleus and participate in chemical reactions with other atoms. The others are called [core electrons](https://en.wikipedia.org/wiki/Core_electron).[^\[43\]^](https://en.wikipedia.org/wiki/Periodic_table#cite_note-49) **ℓ =** **0** **1** **2** **3** **4** **5** **6** **Shell capacity (2*n*^2^)**[^\[44\]^](https://en.wikipedia.org/wiki/Periodic_table#cite_note-50) ------------------------------ ------- ------- ------- ------- ------- ------- ------- --------------------------------------------------------------------------------------------------- **Orbital** **s** **p** **d** **f** **g** **h** **i** ***n* = 1** 1s 2 ***n* = 2** 2s 2p 8 ***n* = 3** 3s 3p 3d 18 ***n* = 4** 4s 4p 4d 4f 32 ***n* = 5** 5s 5p 5d 5f 5g 50 ***n* = 6** 6s 6p 6d 6f 6g 6h 72 ***n* = 7** 7s 7p 7d 7f 7g 7h 7i 98 **Subshell capacity (4ℓ+2)** 2 6 10 14 18 22 26 Elements are known with up to the first seven shells occupied. The first shell contains only one orbital, a spherical s orbital. As it is in the first shell, this is called the 1s orbital. This can hold up to two electrons. The second shell similarly contains a 2s orbital, and it also contains three dumbbell-shaped 2p orbitals, and can thus fill up to eight electrons (2×1 + 2×3 = 8). The third shell contains one 3s orbital, three 3p orbitals, and five 3d orbitals, and thus has a capacity of 2×1 + 2×3 + 2×5 = 18. The fourth shell contains one 4s orbital, three 4p orbitals, five 4d orbitals, and seven 4f orbitals, thus leading to a capacity of 2×1 + 2×3 + 2×5 + 2×7 = 32.[^\[30\]^](https://en.wikipedia.org/wiki/Periodic_table#cite_note-Petrucci331-34) Higher shells contain more types of orbitals that continue the pattern, but such types of orbitals are not filled in the ground states of known elements.[^\[45\]^](https://en.wikipedia.org/wiki/Periodic_table#cite_note-Goudsmit-51) The subshell types are characterized by the [quantum numbers](https://en.wikipedia.org/wiki/Quantum_number). Four numbers describe an orbital in an atom completely: the [principal quantum number](https://en.wikipedia.org/wiki/Principal_quantum_number) *n*, the [azimuthal quantum number](https://en.wikipedia.org/wiki/Azimuthal_quantum_number) ℓ (the orbital type), the [orbital magnetic quantum number](https://en.wikipedia.org/wiki/Magnetic_quantum_number) *m*~ℓ~, and the [spin magnetic quantum number](https://en.wikipedia.org/wiki/Spin_quantum_number) *m~s~*.[^\[39\]^](https://en.wikipedia.org/wiki/Periodic_table#cite_note-FIII19-44) **Order of subshell filling** Idealized order of subshell filling according to the [Madelung rule](https://en.wikipedia.org/wiki/Madelung_rule) The sequence in which the subshells are filled is given in most cases by the [Aufbau principle](https://en.wikipedia.org/wiki/Aufbau_principle), also known as the Madelung or Klechkovsky rule (after [Erwin Madelung](https://en.wikipedia.org/wiki/Erwin_Madelung) and [Vsevolod Klechkovsky](https://en.wikipedia.org/wiki/Vsevolod_Klechkovsky) respectively). This rule was first observed empirically by Madelung, and Klechkovsky and later authors gave it theoretical justification.^[\[46\]](https://en.wikipedia.org/wiki/Periodic_table#cite_note-Jolly-52)[\[47\]](https://en.wikipedia.org/wiki/Periodic_table#cite_note-Ostrovsky-53)[\[48\]](https://en.wikipedia.org/wiki/Periodic_table#cite_note-Ostrovsky1981-54)[\[49\]](https://en.wikipedia.org/wiki/Periodic_table#cite_note-Wong-55)[\[g\]](https://en.wikipedia.org/wiki/Periodic_table#cite_note-lowdin-56)^ The shells overlap in energies, and the Madelung rule specifies the sequence of filling according to:[^\[47\]^](https://en.wikipedia.org/wiki/Periodic_table#cite_note-Ostrovsky-53) 1s ≪ 2s \< 2p ≪ 3s \< 3p ≪ 4s \< 3d \< 4p ≪ 5s \< 4d \< 5p ≪ 6s \< 4f \< 5d \< 6p ≪ 7s \< 5f \< 6d \< 7p ≪ \... Here the sign ≪ means \"much less than\" as opposed to \< meaning just \"less than\".[^\[47\]^](https://en.wikipedia.org/wiki/Periodic_table#cite_note-Ostrovsky-53) Phrased differently, electrons enter orbitals in order of increasing *n* + ℓ, and if two orbitals are available with the same value of *n* + ℓ, the one with lower *n* is occupied first.^[\[45\]](https://en.wikipedia.org/wiki/Periodic_table#cite_note-Goudsmit-51)[\[49\]](https://en.wikipedia.org/wiki/Periodic_table#cite_note-Wong-55)^ In general, orbitals with the same value of *n* + ℓ are similar in energy, but in the case of the s-orbitals (with ℓ = 0), quantum effects raise their energy to approach that of the next *n* + ℓ group. Hence the periodic table is usually drawn to begin each row (often called a period) with the filling of a new s-orbital, which corresponds to the beginning of a new shell.^[\[47\]](https://en.wikipedia.org/wiki/Periodic_table#cite_note-Ostrovsky-53)[\[48\]](https://en.wikipedia.org/wiki/Periodic_table#cite_note-Ostrovsky1981-54)[\[30\]](https://en.wikipedia.org/wiki/Periodic_table#cite_note-Petrucci331-34)^ Thus, with the exception of the first row, each period length appears twice:[^\[47\]^](https://en.wikipedia.org/wiki/Periodic_table#cite_note-Ostrovsky-53) 2, 8, 8, 18, 18, 32, 32, \... The overlaps get quite close at the point where the d-orbitals enter the picture,[^\[50\]^](https://en.wikipedia.org/wiki/Periodic_table#cite_note-Petrucci328-57) and the order can shift slightly with atomic number[^\[51\]^](https://en.wikipedia.org/wiki/Periodic_table#cite_note-Cao-58) and atomic charge.^[\[52\]](https://en.wikipedia.org/wiki/Periodic_table#cite_note-Jorgensen-59)[\[h\]](https://en.wikipedia.org/wiki/Periodic_table#cite_note-65)^ Starting from the simplest atom, this lets us build up the periodic table one at a time in order of atomic number, by considering the cases of single atoms. In [hydrogen](https://en.wikipedia.org/wiki/Hydrogen), there is only one electron, which must go in the lowest-energy orbital 1s. This [electron configuration](https://en.wikipedia.org/wiki/Electron_configuration) is written 1s^1^, where the superscript indicates the number of electrons in the subshell. [Helium](https://en.wikipedia.org/wiki/Helium) adds a second electron, which also goes into 1s, completely filling the first shell and giving the configuration 1s^2^.^[\[39\]](https://en.wikipedia.org/wiki/Periodic_table#cite_note-FIII19-44)[\[58\]](https://en.wikipedia.org/wiki/Periodic_table#cite_note-jensenlaw-66)[\[i\]](https://en.wikipedia.org/wiki/Periodic_table#cite_note-68)^ Starting from the third element, [lithium](https://en.wikipedia.org/wiki/Lithium), the first shell is full, so its third electron occupies a 2s orbital, giving a 1s^2^ 2s^1^ configuration. The 2s electron is lithium\'s only valence electron, as the 1s subshell is now too tightly bound to the nucleus to participate in chemical bonding to other atoms: such a shell is called a \"[core shell](https://en.wikipedia.org/wiki/Core_electron)\". The 1s subshell is a core shell for all elements from lithium onward. The 2s subshell is completed by the next element [beryllium](https://en.wikipedia.org/wiki/Beryllium) (1s^2^ 2s^2^). The following elements then proceed to fill the 2p subshell. [Boron](https://en.wikipedia.org/wiki/Boron) (1s^2^ 2s^2^ 2p^1^) puts its new electron in a 2p orbital; [carbon](https://en.wikipedia.org/wiki/Carbon) (1s^2^ 2s^2^ 2p^2^) fills a second 2p orbital; and with [nitrogen](https://en.wikipedia.org/wiki/Nitrogen) (1s^2^ 2s^2^ 2p^3^) all three 2p orbitals become singly occupied. This is consistent with [Hund\'s rule](https://en.wikipedia.org/wiki/Hund%27s_rule), which states that atoms usually prefer to singly occupy each orbital of the same type before filling them with the second electron. [Oxygen](https://en.wikipedia.org/wiki/Oxygen) (1s^2^ 2s^2^ 2p^4^), [fluorine](https://en.wikipedia.org/wiki/Fluorine) (1s^2^ 2s^2^ 2p^5^), and [neon](https://en.wikipedia.org/wiki/Neon) (1s^2^ 2s^2^ 2p^6^) then complete the already singly filled 2p orbitals; the last of these fills the second shell completely.^[\[39\]](https://en.wikipedia.org/wiki/Periodic_table#cite_note-FIII19-44)[\[58\]](https://en.wikipedia.org/wiki/Periodic_table#cite_note-jensenlaw-66)^ Starting from element 11, [sodium](https://en.wikipedia.org/wiki/Sodium), the second shell is full, making the second shell a core shell for this and all heavier elements. The eleventh electron begins the filling of the third shell by occupying a 3s orbital, giving a configuration of 1s^2^ 2s^2^ 2p^6^ 3s^1^ for sodium. This configuration is abbreviated \[Ne\] 3s^1^, where \[Ne\] represents neon\'s configuration. [Magnesium](https://en.wikipedia.org/wiki/Magnesium) (\[Ne\] 3s^2^) finishes this 3s orbital, and the following six elements aluminium, [silicon](https://en.wikipedia.org/wiki/Silicon), [phosphorus](https://en.wikipedia.org/wiki/Phosphorus), [sulfur](https://en.wikipedia.org/wiki/Sulfur), [chlorine](https://en.wikipedia.org/wiki/Chlorine), and [argon](https://en.wikipedia.org/wiki/Argon) fill the three 3p orbitals (\[Ne\] 3s^2^ 3p^1^ through \[Ne\] 3s^2^ 3p^6^).^[\[39\]](https://en.wikipedia.org/wiki/Periodic_table#cite_note-FIII19-44)[\[58\]](https://en.wikipedia.org/wiki/Periodic_table#cite_note-jensenlaw-66)^ This creates an analogous series in which the outer shell structures of sodium through argon are analogous to those of lithium through neon, and is the basis for the periodicity of chemical properties that the periodic table illustrates:[^\[39\]^](https://en.wikipedia.org/wiki/Periodic_table#cite_note-FIII19-44) at regular but changing intervals of atomic numbers, the properties of the chemical elements approximately repeat.[^\[36\]^](https://en.wikipedia.org/wiki/Periodic_table#cite_note-Scerri17-41) The first eighteen elements can thus be arranged as the start of a periodic table. Elements in the same column have the same number of valence electrons and have analogous valence electron configurations: these columns are called groups. The single exception is helium, which has two valence electrons like beryllium and magnesium, but is typically placed in the column of neon and argon to emphasise that its outer shell is full. (Some contemporary authors question even this single exception, preferring to consistently follow the valence configurations and place helium over beryllium.) There are eight columns in this periodic table fragment, corresponding to at most eight outer-shell electrons.[^\[32\]^](https://en.wikipedia.org/wiki/Periodic_table#cite_note-cartoon-36) A period begins when a new shell starts filling.[^\[30\]^](https://en.wikipedia.org/wiki/Periodic_table#cite_note-Petrucci331-34) Finally, the colouring illustrates the [blocks](https://en.wikipedia.org/wiki/Block_(periodic_table)): the elements in the s-block (coloured red) are filling s-orbitals, while those in the p-block (coloured yellow) are filling p-orbitals.[^\[30\]^](https://en.wikipedia.org/wiki/Periodic_table#cite_note-Petrucci331-34) --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- 1\ 2\ 2×1 = **2** elements\ [H](https://en.wikipedia.org/wiki/Hydrogen) [He](https://en.wikipedia.org/wiki/Helium) 1s  --------------------------------------------- ----------------------------------------------- ----------------------------------------------- --------------------------------------------- ----------------------------------------------- ------------------------------------------- ---------------------------------------------- -------------------------------------------- --------------------------- 3\ 4\ 5\ 6\ 7\ 8\ 9\ 10\ 2×(1+3) = **8** elements\ [Li](https://en.wikipedia.org/wiki/Lithium) [Be](https://en.wikipedia.org/wiki/Beryllium) [B](https://en.wikipedia.org/wiki/Boron) [C](https://en.wikipedia.org/wiki/Carbon) [N](https://en.wikipedia.org/wiki/Nitrogen) [O](https://en.wikipedia.org/wiki/Oxygen) [F](https://en.wikipedia.org/wiki/Fluorine) [Ne](https://en.wikipedia.org/wiki/Neon) 2s 2p 11\ 12\ 13\ 14\ 15\ 16\ 17\ 18\ 2×(1+3) = **8** elements\ [Na](https://en.wikipedia.org/wiki/Sodium) [Mg](https://en.wikipedia.org/wiki/Magnesium) [Al](https://en.wikipedia.org/wiki/Aluminium) [Si](https://en.wikipedia.org/wiki/Silicon) [P](https://en.wikipedia.org/wiki/Phosphorus) [S](https://en.wikipedia.org/wiki/Sulfur) [Cl](https://en.wikipedia.org/wiki/Chlorine) [Ar](https://en.wikipedia.org/wiki/Argon) 3s 3p --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- Starting the next row, for [potassium](https://en.wikipedia.org/wiki/Potassium) and [calcium](https://en.wikipedia.org/wiki/Calcium) the 4s subshell is the lowest in energy, and therefore they fill it.^[\[39\]](https://en.wikipedia.org/wiki/Periodic_table#cite_note-FIII19-44)[\[58\]](https://en.wikipedia.org/wiki/Periodic_table#cite_note-jensenlaw-66)^ Potassium adds one electron to the 4s shell (\[Ar\] 4s^1^), and calcium then completes it (\[Ar\] 4s^2^). However, starting from [scandium](https://en.wikipedia.org/wiki/Scandium) (\[Ar\] 3d^1^ 4s^2^) the 3d subshell becomes the next highest in energy. The 4s and 3d subshells have approximately the same energy and they compete for filling the electrons, and so the occupation is not quite consistently filling the 3d orbitals one at a time. The precise energy ordering of 3d and 4s changes along the row, and also changes depending on how many electrons are removed from the atom. For example, due to the repulsion between the 3d electrons and the 4s ones, at [chromium](https://en.wikipedia.org/wiki/Chromium) the 4s energy level becomes slightly higher than 3d, and so it becomes more profitable for a chromium atom to have a \[Ar\] 3d^5^ 4s^1^ configuration than an \[Ar\] 3d^4^ 4s^2^ one. A similar anomaly occurs at [copper](https://en.wikipedia.org/wiki/Copper), whose atom has a \[Ar\] 3d^10^ 4s^1^ configuration rather than the expected \[Ar\] 3d^9^ 4s^2^.[^\[39\]^](https://en.wikipedia.org/wiki/Periodic_table#cite_note-FIII19-44) These are violations of the Madelung rule. Such anomalies, however, do not have any chemical significance:[^\[52\]^](https://en.wikipedia.org/wiki/Periodic_table#cite_note-Jorgensen-59) most chemistry is not about isolated gaseous atoms,[^\[60\]^](https://en.wikipedia.org/wiki/Periodic_table#cite_note-69) and the various configurations are so close in energy to each other[^\[50\]^](https://en.wikipedia.org/wiki/Periodic_table#cite_note-Petrucci328-57) that the presence of a nearby atom can shift the balance.[^\[39\]^](https://en.wikipedia.org/wiki/Periodic_table#cite_note-FIII19-44) Therefore, the periodic table ignores them and considers only idealized configurations.[^\[38\]^](https://en.wikipedia.org/wiki/Periodic_table#cite_note-Jensen2009-43) At [zinc](https://en.wikipedia.org/wiki/Zinc) (\[Ar\] 3d^10^ 4s^2^), the 3d orbitals are completely filled with a total of ten electrons.^[\[39\]](https://en.wikipedia.org/wiki/Periodic_table#cite_note-FIII19-44)[\[58\]](https://en.wikipedia.org/wiki/Periodic_table#cite_note-jensenlaw-66)^ Next come the 4p orbitals, completing the row, which are filled progressively by [gallium](https://en.wikipedia.org/wiki/Gallium) (\[Ar\] 3d^10^ 4s^2^ 4p^1^) through [krypton](https://en.wikipedia.org/wiki/Krypton) (\[Ar\] 3d^10^ 4s^2^ 4p^6^), in a manner analogous to the previous p-block elements.^[\[39\]](https://en.wikipedia.org/wiki/Periodic_table#cite_note-FIII19-44)[\[58\]](https://en.wikipedia.org/wiki/Periodic_table#cite_note-jensenlaw-66)^ From gallium onwards, the 3d orbitals form part of the electronic core, and no longer participate in chemistry.[^\[57\]^](https://en.wikipedia.org/wiki/Periodic_table#cite_note-KW-64) The s- and p-block elements, which fill their outer shells, are called [main-group elements](https://en.wikipedia.org/wiki/Main-group_element); the d-block elements (coloured blue below), which fill an inner shell, are called [transition elements](https://en.wikipedia.org/wiki/Transition_element) (or transition metals, since they are all metals).[^\[61\]^](https://en.wikipedia.org/wiki/Periodic_table#cite_note-Petrucci326-70) The next eighteen elements fill the 5s orbitals ([rubidium](https://en.wikipedia.org/wiki/Rubidium) and [strontium](https://en.wikipedia.org/wiki/Strontium)), then 4d ([yttrium](https://en.wikipedia.org/wiki/Yttrium) through [cadmium](https://en.wikipedia.org/wiki/Cadmium), again with a few anomalies along the way), and then 5p ([indium](https://en.wikipedia.org/wiki/Indium) through [xenon](https://en.wikipedia.org/wiki/Xenon)).^[\[30\]](https://en.wikipedia.org/wiki/Periodic_table#cite_note-Petrucci331-34)[\[58\]](https://en.wikipedia.org/wiki/Periodic_table#cite_note-jensenlaw-66)^ Again, from indium onward the 4d orbitals are in the core.^[\[58\]](https://en.wikipedia.org/wiki/Periodic_table#cite_note-jensenlaw-66)[\[62\]](https://en.wikipedia.org/wiki/Periodic_table#cite_note-71)^ Hence the fifth row has the same structure as the fourth.[^\[30\]^](https://en.wikipedia.org/wiki/Periodic_table#cite_note-Petrucci331-34) ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ 1\ 2\ 2×1 = **2** elements\ [H](https://en.wikipedia.org/wiki/Hydrogen) [He](https://en.wikipedia.org/wiki/Helium) 1s   ---------------------------------------------- ----------------------------------------------- ---------------------------------------------- ----------------------------------------------- --------------------------------------------- ------------------------------------------------ ------------------------------------------------ ----------------------------------------------- --------------------------------------------- ----------------------------------------------- -------------------------------------------- --------------------------------------------- ----------------------------------------------- ----------------------------------------------- ----------------------------------------------- ----------------------------------------------- ---------------------------------------------- --------------------------------------------- ------------------------------ 3\ 4\ 5\ 6\ 7\ 8\ 9\ 10\ 2×(1+3) = **8** elements\ [Li](https://en.wikipedia.org/wiki/Lithium) [Be](https://en.wikipedia.org/wiki/Beryllium) [B](https://en.wikipedia.org/wiki/Boron) [C](https://en.wikipedia.org/wiki/Carbon) [N](https://en.wikipedia.org/wiki/Nitrogen) [O](https://en.wikipedia.org/wiki/Oxygen) [F](https://en.wikipedia.org/wiki/Fluorine) [Ne](https://en.wikipedia.org/wiki/Neon) 2s  2p 11\ 12\ 13\ 14\ 15\ 16\ 17\ 18\ 2×(1+3) = **8** elements\ [Na](https://en.wikipedia.org/wiki/Sodium) [Mg](https://en.wikipedia.org/wiki/Magnesium) [Al](https://en.wikipedia.org/wiki/Aluminium) [Si](https://en.wikipedia.org/wiki/Silicon) [P](https://en.wikipedia.org/wiki/Phosphorus) [S](https://en.wikipedia.org/wiki/Sulfur) [Cl](https://en.wikipedia.org/wiki/Chlorine) [Ar](https://en.wikipedia.org/wiki/Argon) 3s  3p 19\ 20\ 21\ 22\ 23\ 24\ 25\ 26\ 27\ 28\ 29\ 30\ 31\ 32\ 33\ 34\ 35\ 36\ 2×(1+3+5) = **18** elements\ [K](https://en.wikipedia.org/wiki/Potassium) [Ca](https://en.wikipedia.org/wiki/Calcium) [Sc](https://en.wikipedia.org/wiki/Scandium) [Ti](https://en.wikipedia.org/wiki/Titanium) [V](https://en.wikipedia.org/wiki/Vanadium) [Cr](https://en.wikipedia.org/wiki/Chromium) [Mn](https://en.wikipedia.org/wiki/Manganese) [Fe](https://en.wikipedia.org/wiki/Iron) [Co](https://en.wikipedia.org/wiki/Cobalt) [Ni](https://en.wikipedia.org/wiki/Nickel) [Cu](https://en.wikipedia.org/wiki/Copper) [Zn](https://en.wikipedia.org/wiki/Zinc) [Ga](https://en.wikipedia.org/wiki/Gallium) [Ge](https://en.wikipedia.org/wiki/Germanium) [As](https://en.wikipedia.org/wiki/Arsenic) [Se](https://en.wikipedia.org/wiki/Selenium) [Br](https://en.wikipedia.org/wiki/Bromine) [Kr](https://en.wikipedia.org/wiki/Krypton) 4s 3d 4p 37\ 38\ 39\ 40\ 41\ 42\ 43\ 44\ 45\ 46\ 47\ 48\