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Formation of table salt

Ordinary table salt, sodium chloride (NaCl), may be formed when sodium reacts with chlorine gas.

Crystals of sodium chloride.

A sodium atom is oxidized

When a sodium atom is oxidized, it gives off an electron and turns into a sodium ion, Na⁺.

Energy is required to remove the valence electron from the sodium atom.

• A sodium ion, Na⁺, is formed, as an electron is released.
• The sodium atom now has eight valence electrons (noble gas configuration), which is particularly stable.

A chlorine atom is reduced

When a chlorine atom is reduced, it takes up an electron and turns into a chloride ion, Cl^–.

Energy is released when a chlorine takes up an extra electron.

• A chloride ion, Cl^–, is formed.
• The chloride ion now has eight valence electrons (noble gas configuration), which is particularly stable.

A redox reaction

With words:

• Sodium + chlorine gas → sodium chloride

With Lewis structures:

• When sodium is oxidized by chlorine, both ions that form get eight valence electrons (noble gas configurations).

With electron configurations:

• K

  L

  M

  K

  L

  M

  K

  L

  M

  K

  L

  M

  11p+

  2e–

  8e–

  1e–

  +

  17p+

  2e–

  8e–

  7e–

  →

  11p+

  2e–

  8e–

  0

  +

  17p+

  2e–

  8e–

  8e–

  sodium atom, Na

  chlorine atom, Cl

  sodium ion, Na+

  chlorine ion, Cl–

Oxidation + reduction = redox reaction

We can combine the oxidation reaction and the reduction reaction to a redox reaction by adding the two together.

Chlorine gas consists of chlorine molecules, Cl₂. Because there are two chlorine atoms in each chlorine molecule, two electrons are taken up by each chlorine molecule. Because of this, the oxidation reaction must be taken ×2 before we can add the reactions together.

• The two e^– that are given off in the oxidation reaction are taken up in the reduction. Because of this, we don't need to write them in the redox reaction formula.

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