Negative ions are called anions.
Oxygen is in group 6. An oxygen atom has six electrons in its outer shell. The atom is more stable if it has a full outer shell.
An oxygen atom can gain two electrons to fill its outer shell. It will still have eight positive protons but will now have ten negative electrons. This gives it an overall charge of -2.
This charge is added to the symbol for oxygen, O2-. It is always written as 2- and not -2. The name of oxygen changes when naming it as an ion. The ion is called an oxide ion.
The name of a non-metal ion is different to the name of its element:
|Atom name||Ion name|
Fluorine is in group 7. It has atomic number 9 and mass number 19.
Group 7 non-metals attract an extra electron to complete their outer shell. The outer electron shell gets further from the nucleus moving down the group. This means that the extra electron is less strongly attracted, so the reactivity of group 7 gets less going down the group.