Forming ions - Metals, non-metals and compounds - GCSE Chemistry (Single Science) Revision - OCR 21st Century - BBC Bitesize

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Revise OCR GCSE Chemistry topics including non-metals and ionic compound properties with this BBC Bitesize GCSE Chemistry (OCR 21C) study guide.

An electrically charged is called an . Ions are formed when atoms lose or gain negatively charged .

The number of electrons lost or gained determines the charge of the ion:

  • the number lost is the same as the number of positive charges
  • the number gained is the same as the number of negative charges

The number of and in an ion is the same as in the atom, and is worked out in the same way.

Learn more on ionic bonding in this podcast.

Forming positive ions

Positive ions are called .

Sodium is in group 1. A sodium atom has one electron in its outer shell. The atom is more stable if it has a full outer shell.

A sodium atom can lose its outer electron. It will still have 11 positive protons but only 10 negative electrons. So, the overall charge is +1.

A positive sign is added to the symbol for sodium, Na+. Ions with greater charge include a number in their symbol, for example Al3+ (which has three positive charges).

How a sodium atom becomes a sodium ion when it loses an electron

Figure caption,

A sodium atom loses one electron to form a sodium ion

Question

  • How many electrons are in the outer shell of a magnesium atom?
  • What is the charge of a magnesium ion and what is its symbol?

Question

The atomic number of lithium is 3. Its mass number is 7. How many protons, neutrons and electrons are there in a lithium ion?

Explaining reactivity in group 1

Going down 1, the outer electron is further away from the positive . It is also shielded from the nucleus by more electron shells. Because of this, it becomes easier to lose the outer electron, so the get more reactive moving down the group.

Table showing electronic configurations of group 1 elements, lithium, sodium and potassium. Group 1 elements have similar properties and reactions as they all have one electron in their outer shell.

The depends on the number of electrons and therefore the of the element.

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