Common Ions Based on Groups
Group
(or column)
1
2
15
16
17
Atoms that commonly form ions
Charge on ions
H, Li, Na, K, Rb, Cs
Be, Mg, Ca, Sr, Ba
N, P, As
O, S, Se, Te
F, Cl, Br, I
1+
2+
321-
Why do the atoms in group 1 form a positive ion?
Why do the atoms in group 15 form ions that have a 3- charge?
In ionic compounds, the charges have to be balanced. In other words, the overall charge of the ionic compound
must be zero. For instance,
Na+ and Cl-
The +1 and -1 charge cancel each other out and the net charge of the ionic compound is zero.
K+ and S2- therefore the formula is K2S
Look at the list of the common polyatomic ions and write the formulas for the following elements:
Sodium and hydroxide
NaOH
Lithium and nitrite
LiNO2
Hydrogen and cyanide
HCN
Sodium and perchlorate
NaClO3
Hydrogen and sulfate
H2SO4
Magnesium and nitrite
Mg(NO2) 2
Barium and chlorate
BaClO3
Hydrogen and acetate
HC2H3O2
Strontium and peroxide
SrO2
Cesium and sulfite
Cs2SO3
Hydrogen and arsenate
H3AsO4
Barium and phosphate
Ba3(PO4)2
Aluminum and chromate
Al2(CrO4)2