Here are tables, in which the commonly used acidic and basic radicals are listed. Hope this will help you.
Names of basic radicals
Names of acidic radicals
And, following rules need to be kept in mind while writing the chemical formulae of compounds.
•The valencies or charges on the ions must be balanced. The charge on a cation must be equal in magnitude to the charge on an anion so that the opposite charges cancel each other out and the net charge of the molecule becomes zero.
- In case of CaO, the valency of Ca is +2 and that of O is −2. These are then crossed over and the compound formed is CaO.
Formula of calcium oxide
Symbols Ca O
Charges 2+ 2−
- The charge on Mg2+ is +2 and that on Cl− is −1. Thus, one Mg2+ ion combines with two Cl− ions to form a molecule with the formula MgCl2.
- In case of a compound consisting of a metal and a non-metal, the symbol of the metal is written first.
- In calcium chloride (CaCl2) and zinc sulphide (ZnS), calcium and zinc are metals, so they are written first; chlorine and sulphur are non-metals, so they are written after the metals.
- In case of compounds consisting of polyatomic ions, the polyatomic ions are enclosed in brackets before writing the number to indicate the ratio.
- In case of aluminium sulphate, to balance the charges, two ions combine with one Al3+ ion. Thus the formula for aluminium sulphate is Al2(SO4)3. Here, the brackets with the subscript 3 indicate that three sulphate ions are joined to two aluminium ions.
Formula of aluminium sulphate
Symbols Al SO4
Charges 3+ 2−
The valencies of a few ions are provided below.
H+ = 1, = 2, Br− = 1, Mg2+ = 2 and K+ = 1
Write the formulae for magnesium bromide, magnesium sulphate, hydrogen bromide and potassium sulphate.
•Magnesium bromide: MgBr2
•Magnesium sulphate: MgSO4
•Hydrogen bromide: HBr
•Potassium sulphate: K2SO4