This document contains all the relevant Chemistry definitions and important information that grade 12 students will need to know for both their preliminary and final examinations. Sections included are: Quantitative Chemistry, Chemical Bonding, Electrochemistry, Energy Change and Rates of Reaction,...
,1. Quantitative Chemistry
Mole – SI unit for amount of substance which contains as many
elementary particles as there are in 12g of the carbon-12 isotope.
Isotope – atoms of the same element that have the same number of
protons but different number of neutrons in the nucleus.
Valency – the number of electrons an atom will gain, lose or share in
order to become stable.
Molar mass – the mass in grams of one mole of the substance.
Relative atomic mass – a number which indicates the average mass
of 1 atom of that element in comparison to the mass of 1 carbon-12
atom to which precisely 12 amu have been assigned.
1 mole of any substance contains 6,02 x 1023 mol-1 elementary
particles.
Solute – the substance that is dissolved in the solution. (usually
smaller than solvent)
Solvent – the substance in which another substance is dissolved,
forming a solution.
Solution – a homogenous mixture of solute and solvent.
Concentration – the amount of solute per unit volume of solution.
Limiting reagent – the substance that is used up first and ends the
chemical reaction when it is used up.
Yield – a measure of the extent of a reaction, generally measured by
comparing the amount of product against the amount of product that
is possible.
2
, 2. Chemical Bonding – intramolecular bonds (3 types)
Intramolecular bond – a bond that occurs between atoms within
molecules.
Valence electrons – electrons in the outer most energy level of an
atom.
Lewis diagram – the diagram with the dots and crosses.
Couper notation – with the joining lines.
Covalent bond – a sharing of at least one pair of electrons by 2 non-
metal atoms.
Pure covalent bond (non-polar) – an equal sharing of electrons.
(diatomic molecules, noble gasses, CO2)
Polar covalent bond – unequal sharing of electrons leading to a
dipole forming (as a result of electronegativity difference).
(polyatomic ions)
Dative covalent bond – both electrons come from the same atom.
Electronegativity – a measure of the tendency of an atom to attract a
bonding pair of electrons / the pull that an atom has on shared
electrons.
δ+ = atom with lower electronegativity / δ- = atom with higher
electronegativity.
Lone pairs – the electron pairs in the outermost energy level of the
atom that DO NOT take part in the chemical bonding process.
The greater the charge on the nucleus, the greater the attractive
force is on the shared electron pair, the greater the electronegativity.
The smaller the radius of the atom, the closer the nucleus is to the
shared electron pair, the greater the electronegativity.
Ionic bond – a transfer of electrons with subsequent electrostatic
attraction.
Metallic bond – being between a positive kernel and sea of
delocalised electrons.
3. Chemical bonding – intermolecular forces (4 types)
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