Forming ions
An Electrically charged particle, formed when an atom or molecule gains or loses electrons. is an The smallest part of an element that can exist. or group of atoms with a positive or negative Property of matter that causes a force when near another charge. Charge comes in two forms, positive and negative. For example, a negative charge causes a repulsive force on a neighbouring negative charge.. Ions form when atoms lose or gain Subatomic particle, with a negative charge and a negligible mass relative to protons and neutrons. to obtain a full outer shell:
- Shiny element that is a good conductor of electricity and heat, and which forms basic oxides. atoms lose electrons to form positively charged ions
- Element that is a poor conductor of electricity and heat, and which forms acidic oxides. atoms gain electrons to form negatively charged ions
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Forming positive ions
Metal atoms lose electrons from their outer shell when they form ions:
- the ions are positive, because they have more Subatomic particle with a positive charge and a relative mass of 1. The relative charge of a proton is +1. than electrons
- the ions formed have full outer shells
- the ions have the electronic structure of a noble gas (group 0 element), with a full outer shell
For elements in A vertical column in the periodic table containing elements with similar chemical properties. 1, 2 and 3, the number of electrons lost is the same as the group number.
Forming negative ions
The outer shells of non-metal atoms gain electrons when they form ions:
- the ions formed are negative, because they have more electrons than protons
- the ions have the electronic structure of a noble gas (group 0 element), with a full outer shell
For elements in groups 6 and 7, the charge on the ion is equal to (8 minus group number).
Example of ion charges and groups
| Group | Element | Ion charge | Ion symbol |
| 1 | Na | + | Na+ |
| 2 | Mg | 2+ | Mg2+ |
| 6 | O | 2- | O2- |
| 7 | Cl | - | Cl- |
| Group | 1 |
|---|---|
| Element | Na |
| Ion charge | + |
| Ion symbol | Na+ |
| Group | 2 |
|---|---|
| Element | Mg |
| Ion charge | 2+ |
| Ion symbol | Mg2+ |
| Group | 6 |
|---|---|
| Element | O |
| Ion charge | 2- |
| Ion symbol | O2- |
| Group | 7 |
|---|---|
| Element | Cl |
| Ion charge | - |
| Ion symbol | Cl- |
Worked example
Sulfur is in group 6 of the periodic table. What is the charge on its ions, and is the charge positive or negative?
The charge is negative, since sulfur is a non-metal. The charge on the ion is (8 - 6) = 2.
Question
Iodine is in group 7. What is the charge on its ions, and is the charge positive or negative?
The charge is negative, since iodine is a non-metal. The charge on the ion is (8 - 7) = 1.