GCSE Chemistry revision

Ionic bonding

Chemical bonds, ionic, covalent and metallic

AQA 4.2.1.2 Foundation & Higher

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Key knowledge

Read on screen, then print for Cornell-style active revision.

What Are Ions?

Ions are charged particles formed when atoms lose or gain electrons in order to achieve a full outer electron shell, which gives them stability.
A sodium atom loses one electron to form a sodium ion with a 1+ charge, written as Na⁺.
A chlorine atom gains one electron to form a chloride ion with a 1− charge, written as Cl⁻.

1. What Are Ions? AQA

Notes

Ions are charged particles formed when atoms lose or gain electrons in order to achieve a full outer electron shell, which gives them stability.
A sodium atom loses one electron to form a sodium ion with a 1+ charge, written as Na⁺.
A chlorine atom gains one electron to form a chloride ion with a 1− charge, written as Cl⁻.

Electron Transfer Between Atoms

In reality, ionic bonding involves the transfer of electrons from one atom to another, rather than each atom gaining or losing electrons independently.
Electrons are transferred from a metal atom (which has too many outer electrons) to a nonmetal atom (which needs more electrons to complete its outer shell).
After the transfer, both atoms become ions with full outer shells, making them more stable.

2. Electron Transfer Between Atoms AQA

Notes

In reality, ionic bonding involves the transfer of electrons from one atom to another, rather than each atom gaining or losing electrons independently.
Electrons are transferred from a metal atom (which has too many outer electrons) to a nonmetal atom (which needs more electrons to complete its outer shell).
After the transfer, both atoms become ions with full outer shells, making them more stable.

Electrostatic Attraction & Ionic Bonds

Once electron transfer occurs, the two ions carry opposite charges and are attracted to each other by electrostatic forces.
This electrostatic force of attraction between oppositely charged ions is called an ionic bond.
Ionic bonds are very strong, comparable in strength to covalent bonds.

3. Electrostatic Attraction & Ionic Bonds AQA

Notes

Once electron transfer occurs, the two ions carry opposite charges and are attracted to each other by electrostatic forces.
This electrostatic force of attraction between oppositely charged ions is called an ionic bond.
Ionic bonds are very strong, comparable in strength to covalent bonds.

Dot and Cross Diagrams

Dot and cross diagrams are used to show the arrangement and transfer of electrons when ionic bonds form.
Electrons from one atom are drawn as dots and electrons from the other atom are drawn as crosses, so you can track which electrons came from which atom.
Arrows are used to show the movement of electrons from one atom to another during the transfer.
Ions are shown inside square brackets with their charge written in the top right corner.
You may be asked to draw either all electron shells or just the outermost shell — drawing only the outer shell is quicker and is a common exam instruction.

4. Dot and Cross Diagrams AQA

Notes

Dot and cross diagrams are used to show the arrangement and transfer of electrons when ionic bonds form.
Electrons from one atom are drawn as dots and electrons from the other atom are drawn as crosses, so you can track which electrons came from which atom.
Arrows are used to show the movement of electrons from one atom to another during the transfer.
Ions are shown inside square brackets with their charge written in the top right corner.
You may be asked to draw either all electron shells or just the outermost shell — drawing only the outer shell is quicker and is a common exam instruction.

Example: Formation of Sodium Chloride (NaCl)

Sodium has one outer electron that it transfers to chlorine, which needs one electron to complete its outer shell.
After the transfer, a Na⁺ ion and a Cl⁻ ion are formed, and their opposite charges mean they are attracted to each other, forming an ionic bond.

5. Example: Formation of Sodium Chloride (NaCl) AQA

Notes

Sodium has one outer electron that it transfers to chlorine, which needs one electron to complete its outer shell.
After the transfer, a Na⁺ ion and a Cl⁻ ion are formed, and their opposite charges mean they are attracted to each other, forming an ionic bond.

Harder Example: Formation of Magnesium Chloride (MgCl₂)

Magnesium has two outer electrons and needs to lose both, while each chlorine atom has seven outer electrons and needs one more to complete its shell.
Magnesium transfers one electron to each of the two chlorine atoms, forming a Mg²⁺ ion and two Cl⁻ ions.
In the dot and cross diagram for MgCl₂, the two chloride ions are placed on either side of the magnesium ion to reflect how they would be arranged in a real ionic compound.

6. Harder Example: Formation of Magnesium Chloride (MgCl₂) AQA

Notes

Magnesium has two outer electrons and needs to lose both, while each chlorine atom has seven outer electrons and needs one more to complete its shell.
Magnesium transfers one electron to each of the two chlorine atoms, forming a Mg²⁺ ion and two Cl⁻ ions.
In the dot and cross diagram for MgCl₂, the two chloride ions are placed on either side of the magnesium ion to reflect how they would be arranged in a real ionic compound.

Key Rules for Ionic Bonding

As a general rule, electrons are transferred from the metal atom to the non-metal atom during ionic bond formation.
The number of electrons lost by the metal must equal the total number of electrons gained by the non-metal atoms, ensuring overall charge balance.
The formula of an ionic compound (e.g. MgCl₂) reflects the ratio of ions needed to balance the charges.

7. Key Rules for Ionic Bonding AQA

Notes

As a general rule, electrons are transferred from the metal atom to the non-metal atom during ionic bond formation.
The number of electrons lost by the metal must equal the total number of electrons gained by the non-metal atoms, ensuring overall charge balance.
The formula of an ionic compound (e.g. MgCl₂) reflects the ratio of ions needed to balance the charges.

Key Tips for Exam Dot and Cross Diagrams

Always use dots for one atom's electrons and crosses for the other atom's electrons to clearly distinguish their origins.
Show electron movement with arrows pointing from the atom donating the electron to the atom receiving it.
Place ions in square brackets with their charge shown, and arrange them as they would appear in the real compound when more than two ions are involved.

8. Key Tips for Exam Dot and Cross Diagrams AQA

Notes

Always use dots for one atom's electrons and crosses for the other atom's electrons to clearly distinguish their origins.
Show electron movement with arrows pointing from the atom donating the electron to the atom receiving it.
Place ions in square brackets with their charge shown, and arrange them as they would appear in the real compound when more than two ions are involved.