Forming Ions

An ion is an atom or molecule that has a positive or negative charge. They occur when an atom gains or loses electrons, which changes the number of electrons in the atom’s outer shell.

Metals form positive ions (cations) when they lose electrons from their outer shell. This results in an imbalance of positively charged protons and negatively charged electrons, giving the ion a positive charge. The positive charge on the ion will be equal to the number of electrons the atom has lost.

On the other hand, non-metals form negative ions (anions) when they gain electrons from other atoms. This increases the number of negatively charged electrons compared to positively charged protons, which gives the ion a negative charge. The negative charge on the ion will equal the number of electrons the atom has gained.

The ions formed will have an electronic structure similar to that of a group 0 element. This means that the ions have a full outer shell of electrons.

A red circle with a positive sign represents a cation, a blue circle with a negative sign represents an anion, and a yellow plain circle represents a neutral atom. An arrow going from the neutral atom to the cation indicates a loss of electron(s), while an arrow from the neutral atom to the anion indicates a gain of electron(s).

The table below shows the ion charges for different groups.

Group numberCharge of Ion formedExamples
1+1Na⁺
2+2Mg²
3+3Al³
6-2O²
7-1Cl⁻

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