The formulae for commona anion and cations are given below. These are arranged in order of the appearance of the corresponding element in the periodic table with the numbers in the top row being the group numbers in the periodic table.
| 1 | 2 | | | | | | |
| Li+ | Be2+ | | | N3– | O2– | F– | |
| Na+ | Mg2+ | Al3+ | | P3– | S2– | Cl– | |
| K+ | Ca2+ | | | | | Br– | |
| Rb+ | Sr2+ | | | | | I– | |
| Cs+ | Ba2+ | | | | | | |
The
cations shown are the only monatomic ions formed by that element.
Name is element name followed by ion.
Ca2+ is calcium ion and Li+ is lithium ion.
When writing the formula from the name, recall that the magnitude of the positive charge is equal to the last digit of the Group number.
The
anions in the table are the only monatomic ions formed by that element.
Name using the first part of the element name plus -ide.
H– hydride F– fluoride Cl– chloride
Br– bromide I– iodide
O2– oxide S2– sulfide N3– nitride
When writing the formula from the name, note that with the exception of H– the magnitude of the negative charge is equal to the Group number - 18.
For
ionic compounds containing any pair of these ions.
Name is cation name followed by anion name.
NaCl is sodium chloride.
CaF2 is calcium fluoride.
When writing the formula from name, take account of the fact that the lattice of ionic compounds must have equal numbers of positive and negative charges.
Calcium fluoride must be CaF2 as there must be two F– for each Ca2+.