Make the charges balance.
Ionic substances contain positive and negative ions held by electrostatic attraction in extended structures. A formula unit gives the simplest neutral ratio. Covalent bonds involve shared electron pairs attracted to both nuclei. Transition metals can form several charges, indicated by Roman numerals where needed.
To draw a Lewis structure, count all valence electrons, adjust for ionic charge, connect atoms, then allocate remaining pairs and check electron totals. H normally has a duet; many main-group atoms achieve an octet. A double bond counts as two shared pairs but one region in VSEPR.
Balance ionic charge
Explore the relationship
Integer stoichiometric counts; total positive and negative charge must cancel.
Tap or focus a plotted point to read its values.
View plotted data as a table
| Series | Number of + cations | Required −1 anions |
|---|---|---|
| Required −1 anions | 0 | 0 |
| Required −1 anions | 0.1 | 0.2 |
| Required −1 anions | 0.2 | 0.4 |
| Required −1 anions | 0.3 | 0.6 |
| Required −1 anions | 0.4 | 0.8 |
| Required −1 anions | 0.5 | 1 |
| Required −1 anions | 0.6 | 1.2 |
| Required −1 anions | 0.7 | 1.4 |
| Required −1 anions | 0.8 | 1.6 |
| Required −1 anions | 0.9 | 1.8 |
| Required −1 anions | 1 | 2 |
| Required −1 anions | 1.1 | 2.2 |
| Required −1 anions | 1.2 | 2.4 |
| Required −1 anions | 1.3 | 2.6 |
| Required −1 anions | 1.4 | 2.8 |
| Required −1 anions | 1.5 | 3 |
| Required −1 anions | 1.6 | 3.2 |
| Required −1 anions | 1.7 | 3.4 |
| Required −1 anions | 1.8 | 3.6 |
| Required −1 anions | 1.9 | 3.8 |
| Required −1 anions | 2 | 4 |
| Required −1 anions | 2.1 | 4.2 |
| Required −1 anions | 2.2 | 4.4 |
| Required −1 anions | 2.3 | 4.6 |
| Required −1 anions | 2.4 | 4.8 |
| Required −1 anions | 2.5 | 5 |
| Required −1 anions | 2.6 | 5.2 |
| Required −1 anions | 2.7 | 5.4 |
| Required −1 anions | 2.8 | 5.6 |
| Required −1 anions | 2.9 | 5.8 |
| Required −1 anions | 3 | 6 |
| Required −1 anions | 3.1 | 6.2 |
| Required −1 anions | 3.2 | 6.4 |
| Required −1 anions | 3.3 | 6.6 |
| Required −1 anions | 3.4 | 6.8 |
| Required −1 anions | 3.5 | 7 |
| Required −1 anions | 3.6 | 7.2 |
| Required −1 anions | 3.7 | 7.4 |
| Required −1 anions | 3.8 | 7.6 |
| Required −1 anions | 3.9 | 7.8 |
| Required −1 anions | 4 | 8 |
| Required −1 anions | 4.1 | 8.2 |
| Required −1 anions | 4.2 | 8.4 |
| Required −1 anions | 4.3 | 8.6 |
| Required −1 anions | 4.4 | 8.8 |
| Required −1 anions | 4.5 | 9 |
| Required −1 anions | 4.6 | 9.2 |
| Required −1 anions | 4.7 | 9.4 |
| Required −1 anions | 4.8 | 9.6 |
| Required −1 anions | 4.9 | 9.8 |
| Required −1 anions | 5 | 10 |
| Required −1 anions | 5.1 | 10.2 |
| Required −1 anions | 5.2 | 10.4 |
| Required −1 anions | 5.3 | 10.6 |
| Required −1 anions | 5.4 | 10.8 |
| Required −1 anions | 5.5 | 11 |
| Required −1 anions | 5.6 | 11.2 |
| Required −1 anions | 5.7 | 11.4 |
| Required −1 anions | 5.8 | 11.6 |
| Required −1 anions | 5.9 | 11.8 |
| Required −1 anions | 6 | 12 |
Explore: Choose a +3 cation with −1 anions and identify the smallest neutral count.
Write the formula of magnesium nitride using Mg²⁺ and .
- The lowest common charge magnitude is six.
- Three Mg²⁺ balance two : Mg₃N₂.
Assumed knowledge
Valence electrons and simple ratios.
Learning checkpoints & source
YOUR LEARNING CHECKPOINT- Construct ionic formulas and names.
- Draw Lewis structures and count bonding and lone pairs.