Atom, Element & Periodic Table Notes PDF

# What Is An Atom? - Any element is composed of very tiny small particles called atoms. - The atom is spherical in shape and it consists of three types of sub-atomic particles: protons, neutrons and electrons. - The nucleus contains two types of nucleons: the positively charged Protons (p+) and Neu...

# What Is An Atom? - Any element is composed of very tiny small particles called atoms. - The atom is spherical in shape and it consists of three types of sub-atomic particles: protons, neutrons and electrons. - The nucleus contains two types of nucleons: the positively charged Protons (p+) and Neutral Neutrons (n°). - Nucleons = p+ and n° - Negatively charged electrons (e-) revolving in different shells around a central nucleus. - The atom is electrically neutral. This is because the number of the positive protons (p+) equals the number of the negative electrons (e-). - The outer-most shell is called the "valence shell". It contains the valence electrons, which take part in the chemical reaction. - Mass of atoms is concentrated in its nucleus because protons and neutrons are the heavy particles. | Particles | Porton (p+) | Neutron (n°) | Electron (e-) | |---|---|---|---| | Mass | 1 a.m.u. | 1 a.m.u. | 2000 (Zero) (negligible) | | Charge | +1 | 0/neutral/Nil/no charge | -1 | | Symbol | p+ | n° | e- | *a.m.u. = Atomic mass unit* # What Is Element? - Element is a pure substance that is composed of similar atoms with the same atomic number and same chemical behavior (cannot be split into anything simpler). - Each element is given a symbol, atomic number and mass number. # Atomic (Proton) Number Z It is the number of positive protons (p+) inside the nucleus. *Only in case of a neutral atom, the atomic number (Protons) equals the number of electrons.* # Mass Number (Nucleon Number) A It is the total number of protons and neutrons (p+ + n°) inside the nucleus. Protons + neutrons = nucleons # Symbol of an Element - Atomic number = P - Mass number = p + n **Example: Sodium atom** X 11 Na 23 - Protons = 11 - Neutrons = 23 - 11 = 12 - Electrons = 11 - Mass no. = 23 - Proton (atomic) no. = 11 Number of neutrons = Mass number – Atomic number # Electronic Structure - It represents the arrangement of electrons in the different shell of an atom. It is also called "electronic distribution" or "electronic configuration". - The electrons are arranged according to the following two rules (2n²): - The maximum number of electrons that fills a shell is: - In the first shell: 2 electrons - In the second shell: 8 electrons - In the third shell: 18 electrons (sometimes 8) - In any other shell: 32 electrons - The other shells can hold more than 8 e- but they are stable with 8 e-. - The shell nearest to the nucleus (first shell) is filled first. When it is full, the electrons go into the next shell and so on (2,8,8,...). *N.B.: The outermost shell in an atom is called the 'valence shell'. It contains the valence electrons which take part in the chemical reaction.* *The outermost shell should not contain more than 8 electrons. This is because any shell is saturated with this octet number of electrons. Only the first shell is saturated with two electrons.* *N.B.: The Periodic table is useful in the electronic distribution. Transition metals do not follow the above rule.* # Isotopes - Definition: Isotopes are atoms of the same element, with the same number of protons but different number of neutrons. - In other words: Isotopes have same atomic number (P) but different mass (nucleon) number. - The relative atomic mass of chlorine is 35.5 which is the average of the 2 common isotopes of chlorine: chlorine-35 - 17CI35, and chlorine-37 17C137 **Examples:** 1. Chlorine has 2 isotopes: CI-35 and CI-37 | Isotope | 17 35CI | 17 37CI | |---|---|---| | Mass number | 35 | 37 | | Number of protons (Same) | 17 | 17 | | Number of neutrons (Different) | 18 | 20 | | Number of electrons | 17 | 17 | 2. Hydrogen has 3 isotopes 11H, 2'H, 3'H *Isotpoes have identical chemical properties because they have same number of electrons in the outermost shell (same valence electrons). But, their physical properties are different (e.g. different mass number & density). * *Isotopes can be separated physically not chemically.* # Radioactive Isotopes - Isotopes are either non-radioactive or radioactive (their nuclei is unstable and they emit energy). ## Uses of radioactive isotopes (Radioisotopes): - Medical uses: cobalt-60 (Co-60) in treating cancer. - Industrial uses: uranium-235 (U-235) as fuel in nuclear power stations. *N.B: All fuels must burn (react with oxygen) in order to produce energy except uranium. Uranium produces energy without burning (without gaining oxygen).* # The Periodic Table - Periodic Table is used to classifying elements and to predict their properties. - These elements are arranged in the Periodic Table according to the increase in their atomic numbers (not to their mass numbers). - The Periodic Table consists of seven horizontal rows called periods and eight vertical columns called groups. - Elements could be metals (on the left hand side of the periodic table) or non - metals (on the right hand side of the periodic table) - Across the period, the atomic number as well as the number of electrons in the valence shell increases by one. The metallic character decreases from the left to the right. - Along any group, the number of electrons in the valence shell remains the same and is equal to the Group's number. - Along any group, a new shell is added. - The chemical properties of elements in the same Group are nearly similar (because they have the same number of valance electrons). Therefore, it is easy to predict the properties of an element from its position in the Periodic Table. **Across the period:** - Metallic character decreases across the period. - Non-metallic character increases (change from metallic to non-metallic character) across a period. - The atomic number and the number of valance electrons increase by one. **The group number represents the number of electrons in the outermost shell.** **The period number represents number of shells.** **Example:** - Carbon is in group 4 (because it has 4 electrons in its outermost shell). - Carbon is in period 2 (because it has 2 shells). **Example:** - Flerovium, Fl, atomic number 114: * Predict number of electrons in its outer shell? 4 (as it is in group 4) * Predict number of shells? 7 shells (as it is in period 7) (done without electronic configuration) - 11H is the only atom that has its mass number equal to its atomic number (both numbers is 1) !!! - Because it has no neutrons Protons: 1 Electrons: 1 Neutrons: Zero # Elements ## Chemically: | | **Metals** | **Non-Metals** | |---|---|---| | **Their outer shell is incomplete, it contains: ** | less than 4 electrons | 4 electrons or more | | **They are able to:** | lose electrons and change into positive ions | gain electrons and change into negative ions | | **They are present:** | below the zigzag line | above the zigzag line | | **Elements of Group I are called:** | "alkali metals" | Elements of Group VII are called "halogens" | | **Elements of Group II are called:** | "earth alkali metals" | Elements of Group VIII are called "noble gases" | | **They combine with:** | non-metals by losing of electrons | non-metals can combine with metals be gaining electrons & together by sharing of electrons | ## Physically: | | **Metals** | **Non-Metals** | |---|---|---| | **Solid:** | at room temperature (except mercury which is the only liquid metal) | Solid, liquid or gas (Bromine is the only liquid non-metal) | | **Good conductors of:** | electricity (have free moving electrons) | Poor conductors of electricity (except graphite) | | **Good conductors of:** | heat | Poor conductors of heat | | **Malleable:** | (can be beaten into sheets) and ductile (can be drawn into wires) | Solids are brittle (breakable) | | **Sonorous:** | (make ringing sound when hit) | Not sonororus | | **High melting and boiling point:** | (not all) | Low melting and boiling point (except carbon forms: diamond and graphite) | # The Noble (Inert) Gases - They are present in Group 0 (VIII). - They are unreactive as their outer valence shell is complete where it contains 8 electrons, except for helium that has only 2 electrons. - They are not able to lose, gain or share electrons. - They cannot combine with other elements, and exist as single atoms (monoatomic). ## Uses: - Argon is used to fill light bulbs (as it does not react with the filament and makes the light bulb lasts for a longer time). - Helium is used in filling weather balloons as it is lighter than air. # Don't forget: - All elements are either solids or gases at room temperature except mercury (Hg) which is a liquid metal and bromine (Br₂) is a liquid non-metal. - Elements of Groups III, IV, V, and VI start always with "non-metals" followed by "metals". - Period's number= Number of shells filled with electrons. - Group's number = Number of electrons in the outermost shell. - Exception: Although helium is present in Group VIII, yet it has only two electrons in the outer most shell. - Carbon and silicon (Group IV) do not form ions as the maximum number of electrons that can be lost or gained is only 3 electrons. # Questions 1. Hydrogen was used in the past to fill weather balloons, but now we use helium not hydrogen. Explain why helium replaced hydrogen? **Answer:** Because helium is unreactive while hydrogen is flammable 2. Which has bigger size Na or Mg? (as neutrons increase, atomic size increase) # Sodium (Atom) - lost neutron - lost proton (finger print) - Lost electron **Na (atom)** X 11 Na 23 **Na+** X 11 Na+ 23 **Neon** X 10 Ne 20 - **Isotope** - 11 - Na - 22 - **Ion** - **New element** ## Types of ions: 1. Positive ion, atom that lost electrons (Protons>electrons) 2. Negative ion, atom that gained electrons (electrons>protons) ## Examples: **Stick to the numbers given in the question but if not given so you will get the numbers from your periodic table** - *O*-2: - protons 8 - Neutrons 16-8=8 - Electrons 8+2=10 (From periodic table) - *41K+* : - protons 19 - neutrons 41-19=22 - electrons 19-1=18 (We used 41 (given) and NOT 39 as in periodic table) **NB:** proton number did not change (fingerprint) # Question: How to identify an atom? **Answer:** From its proton no (atomic number) # PROPERTIES OF TRANSITION METALS (iron) ## Physical Properties: - They have: - High density - High strength - High melting points ## Chemical Properties: 1. They form colored compounds. (e.g copper sulfate is blue) 2. The metals and their compounds can act as a catalyst. 3. Most of them form ions having more than one oxidation state. e.g. Fe+2 & Fe+3 **Catalyst:** it is a substance which can accelerate the rate of a reaction. It remains chemically unchanged during the reaction. | Q | | A | |---|---|---| | Q1 | What evident in the P.T. proves that all elements had been considered? | Because all atomic numbers are mentioned and there is no empty space in the Periodic Table. | | Q2 | What evident in Period 5 of the P.T. proves that all elements are arranged according to their atomic numbers but not according to their mass numbers? | Tellurium [52Te128] and iodine [53[127]. | | Q3 | Why the bridge is made of iron (as steel) rather than of aluminium metal? | Because iron is a transition metal and it has much better strength. | | Q4 | Why the body of an airplane is made of aluminium metal not from iron? | Because aluminium is much lighter than iron. | | Q5 | Why the shelves of an oven are made of iron metal not from aluminium?| Because iron is a transition metal and has higher melting point. | | Q6 | Which of the following salts is coloured? Explain your answer. Al2(SO4)3 CaSO4 Na2SO4 CuSO4 | Copper (II) sulphate since it contains a transition metal. | **Tricks:** electronic structure of Sr is 2, 8, 8, ........ .. | Property | | Color | |---|---|---| | Iron | catalyst | Silver | | Iron compound | yes | colored | | | | FeCl2, FeSO4....etc | # The Illustrative Periodic Table - The periodic table has 8 groups and 7 periods - Metals are on the left of the zigzag line - Non-metals are on the right of the zigzag line - Hydrogen is a non-meal # Elements, Mixtures and Compounds: | | **Element** | **Compound** | **Mixture** | |---|---|---|---| | **Composition** | It is composed of same type of atoms | It is composed of two or more different elements combined together chemically. | It is composed of two or more elements or compounds mixed together (not chemically joined) | | **Separation of components** | Cannot be separated into anything simpler | The components can be separated by chemical reactions | Components can be separated easily by physical methods | | **Properties** | | Different properties from its elements | Every substance keeps its properties | | **Amounts** | | Amounts of its elements are always in the same ratio | Amounts can change | | **Examples** | Na, O2, S8 | NaCI, CO2, water (H2O) | Air (mixture of gases) A mixture of sand and water Alloys (mixture of metals) | - **atoms getting smaller, less metallic** - **fluorine - the most reactive non-metal** - **metals getting more reactive** - **caesium - the most reactive metal available in useful amounts** - **densities and melting points increase down any group** - **transition elements** - ***atoms getting larger, more metallic*** - ***non-metals getting more reactive*** **NB:** Valency = 8 - Valency electrons