Chemistry: The Central Science - Chapter 2 - Atoms, Molecules, and Ions PDF

Chemistry: The Central Science Fifteenth Edition Chapter 2 Atoms, Molecules, and Ions Copyright © 2023 Pearson Education, Inc. All Rights Reserved 2.1 Atomic Theory of Matter Some Greek philosoph...

Chemistry: The Central Science Fifteenth Edition Chapter 2 Atoms, Molecules, and Ions Copyright © 2023 Pearson Education, Inc. All Rights Reserved 2.1 Atomic Theory of Matter Some Greek philosophers like Democritus believed that there was a smallest particle—“atomos” (uncuttable)— that made up all of nature. Experiments in the eighteenth and nineteenth centuries led to an organized atomic theory by John Dalton in the early 1800s: – The law of constant composition – The law of conservation of mass – The law of multiple proportions Copyright © 2023 Pearson Education, Inc. All Rights Reserved Law of Constant Composition We introduced this in Chapter 1. Compounds have a definite composition. That means that the relative number of atoms of each element in the compound is the same in any sample. – H2O, CO, CO2 This law was discovered by Joseph Proust. This law was one of the laws on which Dalton’s atomic theory (Postulate 4) was based. Copyright © 2023 Pearson Education, Inc. All Rights Reserved Law of Conservation of Mass The total mass of substances present at the end of a chemical process is the same as the mass of substances present before the process took place. This law is further explained in Chapter 3. This law was discovered by Antoine Lavoisier. This law was one of the laws on which Dalton’s atomic theory (Postulate 3) was based. Copyright © 2023 Pearson Education, Inc. All Rights Reserved Law of Multiple Proportions If two elements, A and B, form more than one compound, the masses of B that combine with a given mass of A are in the ratio of small whole numbers. When two or more compounds exist from the same elements, they cannot have the same relative number of atoms, i.e. carbon monoxide CO (poisonous gas) versus carbon dioxide CO2 (what we exhale). John Dalton discovered this law while developing his atomic theory. Copyright © 2023 Pearson Education, Inc. All Rights Reserved Postulates of Dalton’s Atomic Theory (1 of 4) 1) Each element is composed of extremely small particles called atoms. Copyright © 2023 Pearson Education, Inc. All Rights Reserved Postulates of Dalton’s Atomic Theory (2 of 4) 2) All atoms of a given element are identical to one another in mass and other properties, but the atoms of one element are different from the atoms of all other elements. Copyright © 2023 Pearson Education, Inc. All Rights Reserved Postulates of Dalton’s Atomic Theory (3 of 4) 3) Atoms of an element are not changed into atoms of a different element by chemical reactions; atoms are neither created nor destroyed in chemical reactions. Copyright © 2023 Pearson Education, Inc. All Rights Reserved Postulates of Dalton’s Atomic Theory (4 of 4) 4) Atoms of more than one element combine to form compounds; a given compound always has the same relative number and kind of atoms. Copyright © 2023 Pearson Education, Inc. All Rights Reserved 2.2 Discovery of Subatomic Particles In Dalton’s view, the atom was the smallest particle possible. Many discoveries led to the fact that the atom itself was made up of smaller particles. – Electrons and cathode rays – Radioactivity – Nucleus, protons, and neutrons – Today, we can measure the properties of individual atoms and even obtain images of them, that is, silicon Copyright © 2023 Pearson Education, Inc. All Rights Reserved Cathode Rays Streams of negatively charged particles were found to emanate from cathode tubes, causing fluorescence. J. J. Thomson is credited with his discovery (1897). Copyright © 2023 Pearson Education, Inc. All Rights Reserved The Electron Thomson’s measurements allowed for calculation of the charge/mass ratio of the electron. 1.76 108 coulombs/gram (C/g). Copyright © 2023 Pearson Education, Inc. All Rights Reserved Millikan Oil-Drop Experiment Once the charge/mass ratio of the electron was known, determination of either the charge or the mass of an electron would yield the other. Robert Millikan determined the charge on the electron in 1909 was 1.602 10  19 C. Electron mass now known. Copyright © 2023 Pearson Education, Inc. All Rights Reserved Radioactivity (1 of 2) Radioactivity is the spontaneous emission of high- energy radiation by an atom. It was first observed by Henri Becquerel. Marie and Pierre Curie also studied it. Its discovery showed that the atom had more subatomic particles and energy associated with it. Copyright © 2023 Pearson Education, Inc. All Rights Reserved Radioactivity (2 of 2) Three types of radiation were discovered by Ernest Rutherford: –  particles (positively charged) –  particles (negatively charged, like electrons) –  rays (uncharged) Copyright © 2023 Pearson Education, Inc. All Rights Reserved The Atom, Circa 1900 The prevailing theory was that of the “plum pudding” model, put forward by J. J. Thomson. It featured a positive sphere of matter with negative electrons embedded in it. Copyright © 2023 Pearson Education, Inc. All Rights Reserved Discovery of the Nucleus Ernest Rutherford shot  particles at a thin sheet of gold foil and observed the pattern of scatter of the particles. Copyright © 2023 Pearson Education, Inc. All Rights Reserved The Nuclear Atom Since some particles were deflected at large angles, Thomson’s model could not be correct. This led to the nuclear view of the atom. Copyright © 2023 Pearson Education, Inc. All Rights Reserved 2.3 Modern View of Atomic Structure Rutherford postulated a very small, dense positive center with the electrons around the outside. We now know that most of the atom is empty space. – Atoms are very small; 1–5 Å or 100–500 pm. – Other subatomic particles (protons and neutrons in the nucleus) discovered. Copyright © 2023 Pearson Education, Inc. All Rights Reserved Subatomic Particles Protons (+1) and electrons (  1) have a charge; neutrons are neutral. Protons and neutrons have essentially the same mass (relative mass 1). The mass of an electron is so small we ignore it (relative mass 0). Protons and neutrons are found in the nucleus; electrons travel around the nucleus. Table 2.1 Comparison of the Proton, Neutron, and Electron Particle Charge Mass (amu) Proton Positive (1+) 1.0073 Neutron None (neutral) 1.0087 Electron Negative (1 ) left parenthesis 1 minus right parenthesis 5.486 10  4 5.486 times 10 to the negative fourth power Copyright © 2023 Pearson Education, Inc. All Rights Reserved Atomic Number How do we determine which element an atom is? Atomic Number: The number of protons in the nucleus of an atom. Since atoms have no overall charge, the number of protons equals the number of electrons in an atom. Copyright © 2023 Pearson Education, Inc. All Rights Reserved Atoms of an Element Elements are represented by a one or two letter symbol, for which the first letter is always capitalized. C is the symbol for carbon. All atoms of the same element have the same number of protons, which is called the atomic number. It is written as a subscript before the symbol. 6 is the atomic number for carbon. The mass number is the total number of protons and neutrons in the nucleus of an atom. It is written as a superscript before the symbol. Copyright © 2023 Pearson Education, Inc. All Rights Reserved Isotopes Isotopes are atoms of the same element with different masses. Isotopes have different numbers of neutrons, but the same number of protons. The table below lists four isotopes for carbon. Table 2.2 Some Isotopes of Carbona Symbol Number of Protons Number of Electrons Number of Neutrons 11 C Carbon 11 6 6 5 12 C Carbon 12 6 6 6 13 C Carbon 13 6 6 7 14 C Carbon 14 6 6 8 a Almost 99% of the carbon found in nature is 12 C. Copyright © 2023 Pearson Education, Inc. All Rights Reserved 2.4 Atomic Mass Unit (amu) Atoms have extremely small masses. In 100 g water, there are 1) 1.1 g of H and 88.9 g of O. rams and 2) Two H for each O. H was arbitrarily assigned a mass of 1. Masses of all other atoms were assigned relative to H, that is, O = 16. Today we can determine the mass to high degree of accuracy and precision. A mass scale on the atomic level is used, where an atomic mass unit (amu) is the base unit. 1 amu 1.66054 10  24 g Copyright © 2023 Pearson Education, Inc. All Rights Reserved Atomic Weight Because in the real world we use large amounts of atoms and molecules, we use average masses in calculations. An average mass is found using all isotopes of an element weighted by their relative abundances. This is the element’s atomic weight. Atomic Weight  [(isotope mass) (fractional natural abundance)] for ALL isotopes. The masses of any atom is compared to C-12 (6 protons and 6 neutrons) being exactly 12. Copyright © 2023 Pearson Education, Inc. All Rights Reserved Atomic Weight Measurement Atomic and molecular weight can be measured using a mass spectrometer (below). The spectrum of chlorine showing two isotopes is seen on the right. Isotope abundance can also be determined this way. Copyright © 2023 Pearson Education, Inc. All Rights Reserved 2.5 Periodic Table The periodic table is a systematic organization of the elements. Elements are arranged in order of atomic number. Accessible periodic media.pearsoncmg.com table: Copyright © 2023 Pearson Education, Inc. All Rights Reserved Reading the Periodic Table Boxes on the periodic table list the atomic number Above the symbol. The atomic weight of an element is listed below the symbol on the periodic table. Copyright © 2023 Pearson Education, Inc. All Rights Reserved Organization of the Periodic Table The rows on the periodic table are called periods. Columns are called groups. Elements in the same group have similar chemical properties. Copyright © 2023 Pearson Education, Inc. All Rights Reserved Periodicity—Rows When one looks at the chemical properties of elements in a row, one notices a repeating pattern of properties and reactivity. Copyright © 2023 Pearson Education, Inc. All Rights Reserved Groups—Columns Groups are the columns of the periodic table The five groups are known by name. Table 2.3 Names of Some Groups in the Periodic Table Group Name Elements 1A Alkali metals Li, Na, K, Rb, Cs, Fr 2A Alkaline earth metals Be, Mg, Ca, Sr, Ba, Ra 6A Chalcogens O, S, Se, Te, Po 7A Halogens F, Cl, Br, I, At 8A Noble gases He, Ne, Ar, Kr, Xe, Rn Copyright © 2023 Pearson Education, Inc. All Rights Reserved Periodic Table (1 of 3) Metals are on the left side of the periodic table. Some properties of metals include: – Shiny luster – Conducting heat and electricity – Solids (except mercury) Copyright © 2023 Pearson Education, Inc. All Rights Reserved Periodic Table (2 of 3) Nonmetals are on the right side of the periodic table (they include H). They can be solid (like carbon), liquid (like bromine), or gas (like neon) at room temperature. Copyright © 2023 Pearson Education, Inc. All Rights Reserved Periodic Table (3 of 3) Elements on the steplike purple line are metalloids (except Al, Po, and At). Their properties are sometimes like metals and sometimes like nonmetals. Copyright © 2023 Pearson Education, Inc. All Rights Reserved 2.6 Molecules and Molecular Compounds Chemical Formula: The subscript to the right of the symbol of an element tells the number of atoms of that element in one molecule of the compound. Molecular compounds: They are composed of molecules and almost always contain only nonmetals. Copyright © 2023 Pearson Education, Inc. All Rights Reserved Diatomic Molecules These seven elements occur naturally as molecules containing two atoms: – Hydrogen H2  – Nitrogen N2  – Oxygen O2  – Fluorine F2  – Chlorine Cl2  – Bromine Br2  Note their location on – Iodine I2  the periodic table Copyright © 2023 Pearson Education, Inc. All Rights Reserved Types of Formulas Empirical formulas give the lowest whole-number ratio of atoms of each element in a compound. Molecular formulas give the exact number of atoms of each element in a compound. If we know the molecular formula of a compound, we can determine its empirical formula. The converse is not true without more information. Copyright © 2023 Pearson Education, Inc. All Rights Reserved Picturing Molecules Structural formulas (2D) show the order in which atoms are attached. They do NOT depict the three-dimensional (3D) shape of molecules. Perspective drawings, ball-and-stick models, and space- filling models show the three-dimensional (3D) order of the atoms in a compound. Copyright © 2023 Pearson Education, Inc. All Rights Reserved 2.7 Ions and Ionic Compounds When an atom of a group of atoms loses or gains electrons, it becomes an ion. Cations are formed when at least one electron is lost. Monatomic cations are formed by metals. Anions are formed when at least one electron is gained. Monatomic anions are formed by nonmetals, except the noble gases. Copyright © 2023 Pearson Education, Inc. All Rights Reserved Ionic Compounds Ionic compounds (such as NaCl) are generally formed between metals and nonmetals. Electrons are transferred from the metal to the nonmetal. The oppositely charged ions attract each other. Only empirical formulas are written. Copyright © 2023 Pearson Education, Inc. All Rights Reserved 2.8 Naming Inorganic Compounds The system of naming compounds is called chemical nomenclature. Names of ions (cations and anions) must be memorized There are rules used to name: 1) Ionic compounds 2) Acids 3) Binary molecular compounds Copyright © 2023 Pearson Education, Inc. All Rights Reserved Common Cations (1 of 2) Table 2.4 Common Cationsa Charge Formula Name Formula Name 1+ H H plus hydrogen ion NH4  N H 4 plus ammonium ion lithium ion copper(I) or cuprous ion Blank Li Cu Copper 1 L i plus C u plus sodium ion Blank Blank Blank Na N a plus  potassium ion Blank Blank Blank K K plus  cesium ion Blank Blank Blank Cs C s plus  Ag silver ion Blank Blank Blank A g plus Copyright © 2023 Pearson Education, Inc. All Rights Reserved Common Cations (2 of 2) Table 2.4 [continued] Charge Formula Name Formula Name 1+ Mg2 magnesium ion cobalt(II) or cobaltous ion Co2 C o 2 plus M g 2 plus cobalt, 2 Ca2 calcium ion Cu2 copper(II) or cupric ion Blank C u 2 plus C a 2 plus copper, 2 strontium ion iron(II) or ferrous ion Blank Sr 2 Fe2 S r 2 plus F e 2 plus iron, 2 barium ion Blank Ba2 B a 2 plus Mn2 M n 2 plus manganese(II) or manganous ion Manganese, 2 Zn2 zinc ion Blank Z n 2 plus Hg22 H g 2, 2 plus mercury(I) or mercurous ion mercury, 1 Cd2 cadmium ion Blank C d 2 plus Hg2 H g 2 plus mercury(II) or mercuric ion mercury, 2 Ni2 nickel(II) or nickelous ion Blank Blank Blank N i 2 plus nickel, 2 Pb2 lead(II) or plumbous ion Blank Blank Blank P b 2 plus lead, 2 Sn2+ tin(II) or stannous ion Blank Blank Blank S n 2 plus tin, 2 a The ions we use most often in this course are in boldface. Learn them first. Copyright © 2023 Pearson Education, Inc. All Rights Reserved Common Anions (1 of 2) Table 2.5 Common Anionsa Charge Formula Name Formula Name hydride ion CH3COO  (or C2H3O2  ) acetate ion 1 1 minus H H minus C H 3 C O O minus, or C 2 H 3 O 2 minus fluoride ion ClO3  chlorate ion Blank F  F minus C l O 3 minus chloride ion perchlorate ion Blank CI C l minus ClO4  C l O 4 minus bromide ion NO3  nitrate ion Br  Blank B r minus N O 3 minus iodide ion MnO4  permanganate ion Blank I I minus M n O 4 minus cyanide ion CN  Blank Blank Blank C N minus hydroxide ion OH  Blank Blank Blank O H minus Copyright © 2023 Pearson Education, Inc. All Rights Reserved Common Anions (2 of 2) Table 2.5 [continued] Charge Formula Name Formula Name oxide ion carbonate ion 2 2 minus O2 O 2 minus CO32 C O 3, 2 minus Blank O2 2 O 2, 2 minus peroxide ion CrO4 2 C r O 4, 2 minus chromate ion sulfide ion Cr2O7 2 dichromate ion Blank S2  S 2 minus C r 2 O 7, 2 minus sulfate ion SO4 2  Blank Blank Blank S O 4, 2 minus nitride ion phosphate ion 3 3 minus N3 N 3 minus PO 4 3  P O 4, 3 minus Copyright © 2023 Pearson Education, Inc. All Rights Reserved Polyatomic Ions Sometimes a group of atoms will gain or lose electrons. These are polyatomic ions. A polyatomic cation: – Ammonium NH4+ A polyatomic anion: – Sulfate SO 4 2 Copyright © 2023 Pearson Education, Inc. All Rights Reserved Writing Inorganic Formulas Because compounds are electrically neutral, one can determine the formula of a compound this way: – The charge on the cation becomes the subscript on the anion. – The charge on the anion becomes the subscript on the cation. – If these subscripts are not in the lowest whole-number ratio, divide them by the greatest common factor. Copyright © 2023 Pearson Education, Inc. All Rights Reserved Naming Inorganic Compounds The cation is named before the anion. Write the element name of the cation. – If the cation can have more than one possible charge, write the charge as a Roman numeral in parentheses, i.e., for iron: Fe2 is iron(II), Fe3 is iron (III). – If it is a polyatomic cation, it will end in –ium, i.e., NH4  ammonium. If the element is the anion, change its ending to –ide, i.e., chlorine: Cl chloride. If the anion is a polyatomic ion, simply write the name of the polyatomic ion, i.e., PO43 phosphate. Copyright © 2023 Pearson Education, Inc. All Rights Reserved Patterns in Oxyanion Nomenclature (1 of 3) When there are only two oxyanions involving the same element – the one with fewer oxygens ends in -ite. – the one with more oxygens ends in -ate. ▪ NO2 : nitrite; NO3  : nitrate ▪ SO3 2 : sulfite; SO4 2 : sulfate Copyright © 2023 Pearson Education, Inc. All Rights Reserved Patterns in Oxyanion Nomenclature (2 of 3) Central atoms on the second row have a bond to, at most, three oxygens; those on the third row take up to four. Ion charges decrease as you go from left to right. Copyright © 2023 Pearson Education, Inc. All Rights Reserved Patterns in Oxyanion Nomenclature (3 of 3) Halogen oxyanions The ion with two oxygens ends in -ite: CIO2  is chlorite. The ion with three oxygens ends in -ate: CIO3  is chlorate. The ion with one oxygen has the prefix hypo- and ends in -ite: CIO is hypochlorite. The ion with four oxygens has the prefix per- and ends in -ate: CIO4  is perchlorate. Copyright © 2023 Pearson Education, Inc. All Rights Reserved Inorganic Acid Nomenclature If the anion of the acid ends in -ide, change the ending to -ic acid and add the prefix hydro-. – HCl: hydrochloric acid – HBr: hydrobromic acid – HI: hydroiodic acid If the anion ends in -ite, change the ending to -ous acid. – HClO: hypochlorous acid – HCl O2 : chlorous acid If the anion ends in -ate, change the ending to -ic acid. – HCl O3 : chloric acid – HCl O4 : perchloric acid Copyright © 2023 Pearson Education, Inc. All Rights Reserved Nomenclature of Binary Molecular Compounds The name of the element Table 2.6 Prefixes Used in farther to the left in the Naming Binary Compounds Formed between Nonmetals periodic table (closer to Prefix Meaning the metals) or lower in the mono- 1 same group is usually di- 2 written first. tri- 3 tetra- 4 A prefix is used to denote penta- 5 the number of atoms of hexa- 6 each element in the hepta- 7 octa- 8 compound (mono- is not nona- 9 used on the first element deca- 10 listed, however). Copyright © 2023 Pearson Education, Inc. All Rights Reserved Nomenclature of Binary Compounds The ending on the second element is changed to -ide. – CO2 : carbon dioxide – CCl4 : carbon tetrachloride If the prefix ends with a or o and the name of the element begins with a vowel, the two successive vowels are often elided into one. – N2O5 : dinitrogen pentoxide – CO: carbon monoxide Copyright © 2023 Pearson Education, Inc. All Rights Reserved 2.9 Some Simple Organic Compounds Organic chemistry is the study of carbon. Organic chemistry has its own system of nomenclature. The simplest hydrocarbons (compounds containing only carbon and hydrogen) are alkanes. The first part of the names just listed correspond to the number of carbons (meth- = 1, eth- = 2, prop- = 3, etc.). It is followed by -ane. Copyright © 2023 Pearson Education, Inc. All Rights Reserved Nomenclature of Alcohols When a hydrogen in an alkane is replaced with something else (a functional group, like  OH in the compounds above), the name is derived from the name of the alkane. The ending denotes the type of compound. – An alcohol ends in -ol. Copyright © 2023 Pearson Education, Inc. All Rights Reserved Nomenclature Isomers: Alcohols When two or more molecules have the same chemical formula, but different structures, they are called isomers. 1-Propanol and 2-propanol have the oxygen atom connected to different carbon atoms. Both have the same empirical and molecular formula (C3H8O). They have different structural formulas: 1 - Propanol : CH3CH2OH 2 - Propanol : CH3CH(OH)CH3 Copyright © 2023 Pearson Education, Inc. All Rights Reserved Copyright This work is protected by United States copyright laws and is provided solely for the use of instructors in teaching their courses and assessing student learning. Dissemination or sale of any part of this work (including on the World Wide Web) will destroy the integrity of the work and is not permitted. The work and materials from it should never be made available to students except by instructors using the accompanying text in their classes. All recipients of this work are expected to abide by these restrictions and to honor the intended pedagogical purposes and the needs of other instructors who rely on these materials. Copyright © 2023 Pearson Education, Inc. All Rights Reserved