Chemistry Notes PDF

## Essential NOTES ONLY - Matter - made up of small particles called atoms and molecule. - Different kinds of atoms and molecules have different properties. - Different kinds of matter show different properties. ### Law of Chemical Combination Atoms combine to form matter. There are 2 laws which...

## Essential NOTES ONLY - Matter - made up of small particles called atoms and molecule. - Different kinds of atoms and molecules have different properties. - Different kinds of matter show different properties. ### Law of Chemical Combination Atoms combine to form matter. There are 2 laws which are followed. - **Law of Conservation of Mass.** - Mass can neither be created nor destroyed. - Given by Antoine Lavoisier in 1774. - The substances which combine together in a chemical reaction are called reactants and the new substance formed is called products. - Total mass of product = Total mass of reactant (product) - eg: Calcium Carbonate (CaCO3) reacts with CO2 100g 56 + 44 - **Law of Constant Proportion.** - A chemical component is always made up of the same elements combined together in a fixed ratio by mass. - Given by Joseph Proust in 1779. - Eg: Carbon Isocyanide can be prepared by the following method: - By escalation - By burning carbon in air - By heating Calcium Carbonate - By heating hydrogen carbonate - Whatever is the source of CO2 it is made up of/C+O/ that is 15:8 (% of element in compound is also same) - % of element in compound = (mass of element / mass of compound) x 100 ### Dalton's Atomic Theory The postulates are: 1. All matter is made up of tiny particles which are called atoms. 2. Atoms are indivisible particles and cannot be created or destroyed in a chemical compound. 3. Atoms of a given element are identical in shape, size, mass and chemical properties. 4. Atoms of different elements are different in shape, size, mass and chemical properties. 5. Atoms combine in a ratio of small whole numbers to form compounds. 6. The relative number and kind of atoms are constant in a compound. ### Relationship of Dalton's atomic theory with laws of chemical combinations. - **Law of conservation of mass**: Atoms are invisible particles and cannot be created or destroyed in a chemical compound. - **Law of constant proportions**: The relative number and kind of atoms are constant in a compound. ### Limitations of Dalton's Atomic Theory - Atom is no longer considered as the smallest invisible particle. It can be divided into 3 different sub-atomic particles: - Electron (-ve) - Proton (+ve) - Neutron (neutral) - Atom is not the smallest particle and can be further divided into sub-atomic particles such as electrons, protons and neutrons. - Atoms of the same element may have different masses. eg:- Chlorine → 35u --> isotopes - Atoms of different elements may have the same masses. eg: Argon → 40u --> Isobars - Substances made up of the same types of atoms have different properties (Allotropes). Eg: Diamond & Graphite were made of carbon but different. - The ratio in which different atoms combine to form in compound may be fixed and integral but not a simple whole ratio. ### Atoms - Atom is the smallest particle which may or may not be capable of independent existence. - Size of an atom is indicated by 'atomic radius' (nm). 1nm = 10-9 m. - Smallest atom Hydrogen. - Cannot only be seen under scanning tunnelling microscope (STM). ### Symbols - First scientist to use symbols for elements were Dalton. - Dalton's symbols: - Hydrogen H - Carbon C - Oxygen O - Phosphorus P - Sulphur S - Platinum Pt - Iron Fe - Copper Cu - Silver Ag - Gold Au - Lead Pb - Mercury Hg - Modern day symbols (Jom Jakob Berzelius) - First letter - First letter + Another letter - IUPAC (International Union of Pure and Applied Chemistry) approves names of elements by units - O - Oxygen/Narium _Na - Sodium - Atomic mass unit: - Atomic mass of carbon is defined as 12 Atomic mass unit of a different isotope of an element. - How do atoms occur? - Molecules - Ions ### Molecules - A group of 2 or more atoms which are held together by some kind of attractive force. - These attractive forces are called chemical bonds. ### Types of Molecules 1. Molecules of an element - 1/2 or more atoms of the same element. - Exist in free state. - Not capable of independent existence - Eg:- Nobel gases (Ne, Ar, Xe etc) 2. Diatomic Molecule - Molecule made of 2 atoms from the same atom. 3. Triatomic Molecule - Molecule made up of 3 atoms 4. Tetra Atomic - Molecule of an other compound - molecule = 1atom + 1atom + 1atom + 1atom 5. Poly-Atomic - molecule made of more than 4 atoms. ### Molecules of a compound - Molecule made up of 2 or more atoms from different elements. - Diatomic - 2 atoms of different elements. - Triatomic - 3 atoms of different elements - Tetra Atomic - 4 atoms of different elements - Poly- atomic - more than 4 atoms of different elements. ### Atomicity - The number of atoms present in one molecule of an element is called its atomicity. - Atomicity of noble gases is one - Metals and some other non - metals such as carbon, do not have a simple structure but consist of a very large number of atoms bonded together. - Argon - Monoatomic - Helium - Monoatomic - Oxygen - Diatomic - Hydrogen - Diatomic - Nitrogen - Diatomic - Chlorine - Diatomic - Phosphorus - Tetra - atomic - Sulphur - Poly- atomic ### Ions - Atoms or group of atoms carrying charge ### Cation - Atom loses electrons and acquires positive charge 1. Monovalent cation - loses 1 electron 2. Bivalent cation - loses 2 electrons 3. Trivalent cation - loses 3 electrons ### Anion - Atom gains electrons, it gets negative charge 1. Monovalent anion - gains 1 electron 2. Bivalent anion - gains 2 electrons 3. Trivalent anion - gains 3 electrons ### Polyatomic ions - Group of atoms carrying a charge are called polyatomic ions. - Polyatomic cation - polyatomic with positive charge - Eg: Ammonium (NH4+) - Polyatomic anion - polyatomic with negative charge - Eg: Carbonate (CO3-2) |Ion | Name| |:---|:----- | |NH4+| Ammonium| |NO2-| Nitrite | |NO3-| Nitrate | |SO32-| Sulphite | |SO42-| Sulphate | |HSO4-| Hydrogen Sulphate | |OH-| Hydroxide | |CN-| Cyanide | |PO43-| Phosphate | |HPO42-| Hydrogen Phosphate | |H2PO4-| Dihydrogen Phosphate | |CO32-| Carbonate | |HCO3-| Hydrogen Carbonate | |ClO2-| Hypochlorite | |ClO3-| Chlorite | |ClO4-| Perchlorate | |CH3COO-| Acetate | |MnO4-| Permanganate | |Cr2O72-| Dichromate | |CrO42-| Chromate| |O22-| Peroxide | ### Valency - Valency of an element is defined as the combined capacity of an element, which depends on the number of electrons lost or gained during a chemical reaction. ### Numerical Total weight of oxygen & boron = 0.24g Weight of oxygen = 0.096g Weight of boron = 0.144g % of Oxygen = (mass of oxygen / mass of compound) x 100 = (0.096g / 0.24g) x 100 = 40%