ACJC Summary Definitions for H2 Chemistry

1 ACJC CHEMISTRY DEPARTMENT JC2 H2 Revision 2024 Summary of definitions for H2 This list of definitions may not be exhaustive. Students are to refer to the lecture notes given. Thank you, Chemistry Department Term Definition 1 Relative isotopic mass The relative isotopic mass of an element is the mass of an atom of the isotope relative to 1 12 of the mass of an atom of 12C. 2 Relative atomic mass The relative atomic mass of an element is the average mass of one atom of the element relative to 1 12 of the mass of one atom of 12C. 3 Relative molecular mass (molecules) The relative molecular mass of a molecule is the average mass of one molecule of a substance relative to 1 12 of the mass of an atom of 12C. 4 Relative formula mass (ions/ ionic compounds) The relative formula mass of an ionic compound is the mass of one formula unit of a substance relative to 1 12 of the mass of one atom of 12C. 5 Mole One mole is the a mount of substance that contains 6.02 x 10 23 particles (atoms, molecules, ions, electrons). 6 Empirical formula Empirical formula of a compound is the formula that shows the simplest whole number ratio of the atoms of the different elements in the compound. 7 Molecular formula Molecular formula of a compound is one which shows the actual number of atoms of each element present in one molecule of a compound.

2 8 Disproportionation A disproportionation reaction is a redox reaction in which one species is simultaneously oxidised and reduced. 9 Mass number/ nucleon number Defined as the total number of protons and neutrons in the nucleus of an atom 10 Atomic number / Proton number Defined as the number of protons in the nucleus of an atom 11 Isotopes Isotopes are atoms of the same element with the same number of protons but different number of neutrons. 12 First ionisation energy The first ionisation energy of an element is defined as the energy absorbed to remove one mole of electrons from one mole of gaseous atoms to form one mole of singly charged positive gaseous ions. Example: Ca (g) → Ca+ (g) + e− ∆H1 = +590 kJ mol−1 13 Second ionisation energy The second ionisation energy of an element is defined as the energy absorbed to remove one mole of electrons from one mole of singly charged positive gaseous ions to form one mole of doubly charged positive gaseous ions. Example: Ca+ (g) → Ca2+ (g) + e− ∆H2 = +1150 kJ mol−1 14 Atomic radius Atomic radius is half the shortest inter-nuclear distance found in the structure of the element. 15 Electronegativity Electronegativity is a measure of the ability of an atom in a molecule to attract the shared pair of electrons in a covalent bond. 16 Ionic radius Ionic radius of an ion is the radius of the spherical ion in an ionic compound. 17 Ionic bond Ionic bond is the strong electrostatic attraction between two oppositely charged ions, formed by the tr