Forming negative and positive ions - Higher tier
Forming negative ions (anions)
Atoms gain electrons in their outer shell when they form negative ions, called A negative ion.. These ions are negative because they contain more electrons than protons.
An oxygen atom gains two electrons to form an oxide anion.
Forming positive ions (cations)
Atoms lose electrons from their outer shell when they form positive ions, called A positive ion. . These ions are positive because they contain more protons than electrons.
A sodium atom loses one electron to form a sodium cation.
Examples of ion charges and groups
| Group | Element symbol | Ion Charge | Ion Symbol |
| 1 | Na | + | Na+ |
| 2 | Mg | 2+ | Mg2+ |
| 6 | O | 2- | O2- |
| 7 | Cl | - | Cl- |
| Group | 1 |
|---|---|
| Element symbol | Na |
| Ion Charge | + |
| Ion Symbol | Na+ |
| Group | 2 |
|---|---|
| Element symbol | Mg |
| Ion Charge | 2+ |
| Ion Symbol | Mg2+ |
| Group | 6 |
|---|---|
| Element symbol | O |
| Ion Charge | 2- |
| Ion Symbol | O2- |
| Group | 7 |
|---|---|
| Element symbol | Cl |
| Ion Charge | - |
| Ion Symbol | Cl- |