Atom is the smallest particle of an element
Atomic number gives the number of protons in the nucleus
Molecule is a group of 2 or more atoms chemically bonded together
Compound is made up of 2 or more elements combined in definite proportion by mass
Law of Conservation of Mass states that ‘total mass off substance does not change during a chemical reaction’
Metals and non-metals react to form ionic compounds. Metals give their outer shell electrons to non-metals so that both atoms end up with a stable outer shell of 8 electrons.
When metals lose their outer shell electrons they form POSITIVE ions (cations). When non-metals gain electrons they form NEGATIVE ions (anions). Cations and anions are electrostatically attracted and form ionic compounds.
Covalent compounds form when non-metals share electrons so that each atom has a full outer shell of electrons.
The valency on ions come from the number of electrons lost/gained in order to obtain a complete outer shell. These charges correspond to the group in which the element belongs in the periodic table.
COMBUSTION - substance reacts with oxygen and releases heat and sometime light
Sulfur + Oxygen = Sulfur dioxide
S + O2 = SO2
Magnesium + Oxygen = Magnesium oxide
2Mg + O2 = 2MgO
CORROSION - metals oxidised to surface compounds e.g. oxides, sulfides and carbonates
Iron + Oxygen + Water = Iron oxide + water
Silver + Sulfur = Silver sulfide
PRECIPITATION - 2 soluble ionic compounds react to form an insoluble product called precipitate.
Sodium chloride + silver nitrate = sodium nitrate + silver chloride
ACID ON METALS AND CARBONATE - acid + metal = salt + hydrogen
acid + carbonate = salt + CO2 + water
Sulphuric acid + zinc = zinc sulfate + hydrogen
H2SO4 + Zn = ZnSO4 + H2
Hydrochloric acid + calcium carbonate = calcium chloride + carbon dioxide + water
2HCl + CaCO3 = CaCl2 + CO2 + H2O
NEUTRALISATION - acid + base = salt + water
Hydrochloric acid + sodium hydroxide = sodium chloride + water
HCl + NaOH = NaCl + H2O
DECOMPOSITION - substance absorbs enough energy for bonds to break
Mercury oxide -> mercury + Oxygen
2HgO -> Hg + O2
Copper carbonate -> copper oxide + carbon dioxide
CuCO3 -> CuO + CO2
BASE - metal + waster = metal hydroxide (BASE)
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