1.3 Prediction of structure from names or formulae of compounds
In most cases, we can predict whether a given compound is ionic or covalent from its name or formula. Below
are two suggested steps:
  I. Identify the metallic, non-metallic or polyatomic ionic part of the compound
  II.

Combination

Type of Compound

Example

metallic ion + non-metallic ion

ionic

NaCl

metallic ion + polyatomic ion

ionic

KNO3

non-metal atom + non-metal atom

covalent

CO2

polyatomic ion + polyatomic ion

ionic

(NH4)2SO4
Polyatomic ions

In order to carry out step one correctly, it is important to familiarize yourself with names of the required cations, anions and polyatomic ions.
e.g. SO42– is polyatomic, NOT a non-metallic part consisting of S and O atoms.