Ions

Level 1

Discovering ions

Matter is made of atoms. An atom is electrically neutral because it contains as many protons (positive charges) as electrons (negative charges).

An ion is an atom (or a group of atoms) that has gained or lost one or more electrons. This gives it an electrical charge:

  • Cation: positively charged ion (it has lost electrons)
  • Anion: negatively charged ion (it has gained electrons)

The electrical charge is written at the top right of the symbol.

  Examples:

  • $\text{Na}^+$: sodium cation
  • $\text{Ca}^{2+}$: calcium cation
  • $\text{Cl}^-$: chloride anion
  • $\text{SO}_4^{2-}$: sulfate anion

Origin of the charge of ions

Electrons are found around the nucleus of an atom. They can be exchanged or transferred during chemical reactions. This transfer changes the total charge:

  • A loss of electrons causes an excess of protons.
    • Therefore positive charge → cation.
  • A gain of electrons  causes an excess of electrons  
    • Therefore negative charge → anion.

The charge of the ion is calculated by:

$$\text{Charge} = \text{(nombre de protons)} - \text{(nombre d'électrons)}$$

  Example:

  • A sodium atom (11 protons, 11 electrons) loses 1 electron → 11 protons and 10 electrons → charge $+1$ → $\text{Na}^+$

Ion Generator

C
+6

6

6
Positive charges
+6
Negative charges
−6
Total charge
0
Chemical symbol
C
Carbon Atom (neutral)

Ions in everyday life

Ions are present everywhere around us:

  • In seawater: $\text{Na}^+$, $\text{Cl}^-$. Called sodium chloride (NaCl), its breakdown into ions in water is responsible for salinity.
  • In our body: $\text{K}^+$ (potassium) for muscles, $\text{Ca}^{2+}$ (calcium) for bones
  • In batteries: $\text{Zn}^{2+}$, $\text{Cu}^{2+}$ to produce electricity

They are also involved in phenomena such as electrical conduction in solution, nerve and muscle exchanges, or the corrosion of metals.