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| Question | Answer |
| Dalton's Atomic Theory | 1. All matter is made up of small particles called atoms 2. All atoms are indivisible. They cannot be broken down into simpler particles. 3. Atoms cannot be created or destroyed |
| Cathode Rays | Cathode rays are streams of negatively charged particles called electrons. |
| An Orbital | An orbital is a region in space within which there is a high probability of finding an electron. |
| An Element | An element is a substance that cannot be split up into simpler substances by chemical means. |
| A Triad | A Triad is a group of three elements with similar chemical properties in which the atomic weight of the middle element is approximately equal to the average of the other two. |
| Newlands' Octaves | Newlands Octaves are groups of elements arranged in order of increasing atomic weight, in which the first and eight element of each group have similar properties. |
| Mendeleev's Periodic Law | When elements are arranged in order of increasing atomic weight (relative atomic mass), the properties of the elements vary periodically. |
| Atomic Number | The number of protons in the nucleus of that atom. |
| Modern Period Table | An arrangement of elements in order of increasing atomic number. |
| Modern Periodic Law | When elements are arranged in order of increasing atomic number, the properties of the elements vary periodically. |
| The Mass Number of an Element | The sum of the number of protons and neutrons in the nucleus of an atom of that element. |
| Isotopes | Atoms of the same element (same atomic number) that have a different mass numbers due to the different number of neutrons in the nucleus. |
| Relative Atomic Mass | - The average of the mass numbers of the isotopes of the element, - As they occur naturally, - Taking their abundances into account and, - Expressed on a scale in which the atoms of the carbon-12 isotope have a mass of exactly 12 units. |
| The Aufbau Principle | When building up the electronic configuration of an atom in its ground state, the electrons occupy the lowest available energy level. |
| Hund's Rule of Maximum Multiplicity | When two or more orbitals of equal energy are available, the electrons occupy them singly before filling them in pairs. |
| The Pauli Exclusion Principle | No more than two electrons may occupy an orbital and they must have opposite spin. |
| A Compund | A substance that is made up of two or more different elements combined together chemically. |
| The Octet Rule | When bonding occurs, atoms tend to reach an electron arrangement with eight electrons in the outermost shell. |
| An Ion | A charged atom or group of atoms. |
| An Ionic Bond | The force of attraction between oppositely charged ions in a compound. |
| A Transition Metal | A transition metal is one that forms at least one ion with a partially filled d sublevel. |
| A Molecule | A group of atoms joined together. It is the smallest particle of an element or compound that can exist independently. |
| The Valency of an Element | The number of atoms of hydrogen or any other monovalent element with which each atom of the element combines. |
| Electronegativity | The relative attraction that an atom in a molecule has for the shared pair of electrons in a covalent bond. |
| Van der Waals Forces | Van der Waal forces are weak attractive forces between molecules resulting from the formation of temporary dipoles. |
| Dipole-Dipole Forces | Dipole-Dipole forces are forces of attraction between the negative pole of one molecule and the positive pole of another. |
| Hydrogen Bonds | Hydrogen bonds are particular types of dipole-dipole attractions between molecules in which hydrogen atoms are bonded to nitrogen, oxygen or fluorine. The hydrogen atom carries a partial positive charge and is attracted to the electronegative atom in another molecule. Thus, it acts as a bridge between two electronegative atoms. |
| The Law of Conservation of Mass | The total mass of the products of a chemical reaction is the same as the total mass of the reactants. |
| The Law of Conservation of Matter | In any chemical reaction, matter is neither created nor destroyed but merely changed from one form into another. |
| The Atomic/Covalent Radius of an Atom | Half the distance between the nuclei of two atoms of the same element that are joined together by a single covalent bond. |
| Radioactivity | The spontaneous breaking up of unstable nuclei with the emission of one or more types of radiation. |
| The Half-Life of an Element | The time taken for half the nuclei in any given sample to decay. |
| One Mole of a Substance | The amount of that substance which contains 6x10^23 particles of that substance. |
| Mass of One Mole of an Element | The relative atomic mass in grams. |
| The Relative Molecular Mass of a Compound | - The sum of the relative atomic masses of all the atoms in a molecule of a compound. - The mass of one molecule of that compound compared with one twelfth of the mass of the carbon-12 isotope. |
| A Gas | A substance that has no well-defined boundaries but diffuses rapidly to fill any container in which it is placed. |
| Boyle's Law | At constant temperature, the volume of a fixed mass of gas is inversely proportional to its pressure. |
| Charles' Law | At constant pressure, the volume of a fixed mass of gas is directly proportional to its temperature measured on the Kelvin scale. |
| Gay-Lussac's Law of Combining Volumes | In a reaction between gases, the volumes of the reacting gases and the volumes of any gaseous products are in the ratio of small whole numbers provided that the volumes are measured at the same temperature and pressure. |
| Avogadro's Law | Equal volumes of gases contain equal numbers of molecules, under the same conditions of temperature and pressure. |
| Molar Volume | At s.t.p one mole of any gas occupies a volume of 22.4 litres. |
| Kinetic Theory of Gases | 1. Gases are made up of particle that are in continuous motion, 2. There are no attractive/repulsive forces between the molecules of a gas, 3. Their molecules are so small and widely separated that the actual volume is negligible compared with the space that they occupy, 4. When molecules collide, there is no loss of kinetic energy but there may be a transfer of energy between the colliding particles, 5. The average kinetic energy is proportional to the temperature (Kelvin). |
| An Ideal Gas | An ideal gas is one that obeys all the assumptions of the kinetic theory of gases under all conditions of temperature and pressure. |
| Real Gases differ from Ideal Gases because.. | (i) Forces of attraction and repulsion between the molecules and, (ii) The volume of the molecules is not negligible (especially at high pressure). |
| The Empirical Formula of a compound | The formula showing the simplest whole number ratio of the numbers of different atoms present in the molecule. |
| Molecular Formula | Is equal to Empirical Formula x n, (where n is a whole number) |
| Arrhenius' definition of an Acid | An acid is a substance that dissociates in water to produce H+ ions. |
| Arrhenius' definition of a Base | A base is a substance that dissociates in water to produce OH- ions. |
| Brønsted–Lowry definition of an Acid | An acid of a proton donor. |
| Brønsted–Lowry definition of a Base | A base is a proton acceptor. |
| Acid to Conjugate Base | An acid changes into a conjugate base when it donates a proton. |
| Base to Conjugate Acid | A base changes into a conjugate acid when it accepts a proton. |
| A Conjugate Acid-Base Pair | Any pair consisting of an acid and a base which differ by one proton. |
| Neutralisation | The reaction between an acid and a base to form salt and water. |
| The Concentration of a Solution | The amount of solute that is dissolved in a given volume of solution. |
| A 1 Molar Solution | A solution that contains one mole of the solute dissolved in one litre of solution |
| A Primary Standard | A substance which can be obtained in a stable, pure and soluble solid form so that it can be weighed out and dissolved in water to give a solution of accurately known concentration. |
| A Titration | A laboratory procedure where a measured volume of one solution is added to a known volume of another solution until the reaction is complete. |
| Oxidation of an Element | Oxidation of an element takes place when it loses electrons. |
| Reduction of an Element | Reduction of an element takes place when it gains electrons. |
| An Oxidising Agent | A substance that brings about oxidation in other substances. |
| A Reducing Agent | A substance that brings about reduction in other substances. |
| Oxidation Number | The charge that atom has or appears to have when electrons are distributed according to certain rules. |
| The Rate of Reaction | The change in concentration per unit time of the reactant/product |
| A Catalyst | A substance that alters the rate of a chemical reaction but is not consumed in the reaction. |
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