Cations	(positive ions)	IONS How do I remember the charges? Group 1 metals always have a charge of +1. Group 1 metals like sodium lose 1 electron to gain a full octet (a full outer shell of 8 electrons). Group 2 metals always have a charge of +2. Group 2 metals like magnesium lose 2 electrons to gain a full octet. Group 7 halogens always have a charge of -1. Group 1 metals like sodium lose 1 electron to gain a full octet. Oxygen in ions always has a charge of -2. Whether the oxygen atom is an ion on its own (oxide ion), or part of a molecular ion like hydroxide, oxygen always has two more electrons than it does protons, and so a charge of -2. Nitrogen in ions always has a charge of -3. Carbon and silicon in ions always have a charge of +4. What is an ion? An atom or molecule that has lost or gained electrons. Atoms that are ions are called simple ions. Atoms that are molecules are called molecular ions. Atoms and molecules normally have no overall electric charge. There’s no charge on an atom because the number of positive protons in the nucleus is equal to the number of negative electrons whizzing around the nucleus. The positive and negative charges cancel each other out. If an atom or molecule loses one electron, there is one positively-charged proton that does not have a negatively-charged electron to cancel out its charge. So the overall charge on the atom or molecule is +1. If an atom or molecule gains one electron, there is one negatively-charged electron that does not have a positively-charged proton to cancel out its charge. So the overall charge on the atom or molecule is -1. The same rule applies if more than one electron is gained or lost. If two negative electrons are lost, the amount of negative charge on the atom or molecule decreases, so the resultant (overall) charge becomes more positive. It’s better to say the resultant charge gets more positive or more negative than to talk about the overall charge increasing or decreasing. When considering electric charges, increasing doesn’t always mean getting more positive. Note: when I have written things like “oxygen always has a charge of -2” this isn’t absolutely always true in real life, but it is true for GCSE. Just remember that sometimes they don’t tell you the whole story so that you don’t have to be examined on the tricky reasons for the exceptions to the rules. If you’re annoyed that you’re told to believe things that aren’t true then firstly well done, that’s a good attitude. But secondly, be happy because it’s one more thing that you don’t have to remember for the exam. If you really want to know, in some unusual compounds, oxygen can be O2^2- (peroxide ion) or O2^- (superoxide ion). If you have any other questions, I will find out the answer for you. Email me at chem@benjamin-mills.com.
H^+	Hydrogen
Li^+	Lithium
Na^+	Sodium
K^+	Potassium
Ag^+	Silver
NH4^+	Ammonium
Mg^2+	Magnesium
Ca^2+	Calcium
Be^2+	Beryllium
Cu^2+	Copper(II)
Zn^2+	Zinc
Pb^2+	Lead
Fe^2+	Iron(II)
Fe^3+	Iron(III)
Al^3+	Aluminium
Anions	(negative ions)
OH^-	Hydroxide
F ^-	Fluoride
Cl ^-	Chloride
Br ^-	Bromide
I ^-	Iodide
NO3 ^-	Nitrate
O^2-	Oxide
S^2-	Sulphide
CO3 ^2-	Carbonate
SO4 ^2-	Sulphate*
SiO3 ^2-	Silicate
A-level
ClO^-	Hypochlorite / chlorate(I)
ClO2^-	Chlorite / chlorate(III)
ClO3^-	Chlorate / chlorate(V)
ClO4^-	Perchlorate / chlorate(VII)
CN^-	Cyanide
Co^2+	Cobalt(II)
Co^3+	Cobalt(III)
Cr2O7^2-	Dichromate / dichromate(VI)
Cr^3+	Chromium(III)
CrO4^-	Chromate / chromate(VII)
Cs^+	Caesium
Cu^+	Copper(I)
H3O^+	Oxonium / hydroxonium / hydronium
HCO3^-	Hydrogencarbonate
Mn^2+	Manganese(II)
Mn^3+	Manganese(III)
MnO4^-	Permanganate / manganate(VII)
MnO4^2-	Manganate(VI)
Ni^2+	Nickel(II)
NO2^-	Nitrite / nitrate(III)
NO2^+	Nitronium
PO4^3-	Phosphate
Rb^+	Rubidium
S2O3^2-	Thiosulphate
S2O8^2-	Persulphate / peroxodisulphate
Sc^3+	Scandium
Sn^2+	Tin(II) / Stannous
Sn^4+	Tin(IV) / Stannic
SO3^2-	Sulphite / sulphate(IV)
Sr^2+	Strontium
Ti^3+	Titanium(III)
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