How do metals and non-metals bond by transferring electrons?
Ionic bonding as the transfer of electrons to form charged ions, drawing dot-and-cross diagrams, the giant ionic lattice, and how the structure explains the properties of ionic compounds.
A CCEA GCSE Chemistry answer on ionic bonding, covering how electrons transfer from metals to non-metals to form ions, dot-and-cross diagrams, the giant ionic lattice, and how this structure explains the high melting points, conductivity and solubility of ionic compounds.
Reviewed by: AI editorial process; not yet individually human-reviewed
Have a quick question? Jump to the Q&A page
Jump to a section
What this dot point is asking
CCEA wants you to explain ionic bonding as the transfer of electrons between a metal and a non-metal, draw dot-and-cross diagrams of the ions formed, describe the giant ionic lattice, and use the structure to explain the properties of ionic compounds.
Forming ions by electron transfer
When a metal reacts with a non-metal, electrons transfer from the metal to the non-metal so both reach full outer shells. The charge on the ion equals the number of electrons lost or gained:
- Group 1 metals lose 1 electron, forming +1 ions ().
- Group 2 metals lose 2 electrons, forming +2 ions ().
- Group 7 non-metals gain 1 electron, forming -1 ions ().
- Group 6 non-metals gain 2 electrons, forming -2 ions ().
Dot-and-cross diagrams
A dot-and-cross diagram shows where the electrons go. Use dots for one atom's electrons and crosses for the other's, so you can see which electrons were transferred. The ions are drawn in square brackets with the charge outside, for example and the chloride ion with eight outer electrons as . Only the outer shell is usually shown.
The giant ionic lattice and its properties
The structure explains the properties:
- High melting and boiling points. Many strong electrostatic forces must be overcome, which needs a lot of energy.
- Conduct only when molten or dissolved. In the solid the ions are locked in place and cannot move. When melted or dissolved in water the ions are free to move and carry charge.
- Often soluble in water and brittle. Water can pull the ions apart; a blow that shifts the layers brings like charges together, which repel and split the crystal.
Examples in context
Example 1. Why road salt melts ice. Sodium chloride dissolves readily in water because the polar water molecules pull its ions out of the lattice. Spreading it on roads lowers the freezing point of water, a direct use of the solubility that comes from its ionic structure.
Example 2. Molten salt electrolysis. Aluminium is extracted by melting its ionic ore so the ions become free to move and can be separated at electrodes. The fact that ionic compounds only conduct when molten or dissolved is exactly what makes this industrial process possible.
Try this
Q1. State the charge on the ion formed by an element in Group 2. [1 mark]
- Cue. +2 (it loses two electrons).
Q2. Explain why molten sodium chloride conducts electricity. [2 marks]
- Cue. The ions are free to move when molten, so they can carry charge.
Exam-style practice questions
Practice questions written in the style of CCEA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
CCEA 20194 marksDescribe, using a dot-and-cross diagram for the outer electrons, how sodium and chlorine form sodium chloride.Show worked answer →
Markers want the electron transfer and the resulting ions described and drawn.
Sodium (2,8,1) has one electron in its outer shell. Chlorine (2,8,7) has seven. Sodium transfers its one outer electron to chlorine.
This gives sodium a full outer shell (now 2,8) and a charge of +1, written . Chlorine gains the electron to complete its outer shell (now 2,8,8) and gets a charge of -1, written .
The dot-and-cross diagram should show the sodium ion as with an empty outer shell, and the chloride ion as , using dots for chlorine electrons and a cross for the transferred sodium electron, with square brackets and charges.
Markers reward the transfer of one electron, both ions with correct charges, and full outer shells shown.
CCEA 20213 marksExplain why sodium chloride has a high melting point but does not conduct electricity when solid.Show worked answer →
The marks are for the lattice and the position of the ions.
Sodium chloride is a giant ionic lattice of oppositely charged ions held by strong electrostatic forces of attraction in all directions. Melting it means overcoming these many strong forces, which needs a lot of energy, so the melting point is high.
It does not conduct when solid because the ions are fixed in position in the lattice and cannot move to carry charge. (It only conducts when molten or dissolved, when the ions are free to move.)
Markers reward strong electrostatic forces in a giant lattice for the high melting point, and ions fixed in place for the lack of conduction when solid.
Related dot points
- Covalent bonding as the sharing of electron pairs between non-metal atoms, drawing dot-and-cross diagrams for simple molecules, and the properties of simple molecular substances.
A CCEA GCSE Chemistry answer on covalent bonding, covering how non-metal atoms share pairs of electrons to fill their outer shells, dot-and-cross diagrams for molecules such as hydrogen, water, ammonia and methane, and why simple molecular substances have low melting points and do not conduct.
- Giant covalent structures, the structures and properties of diamond, graphite and silicon dioxide, and how bonding explains hardness, melting point and electrical conductivity.
A CCEA GCSE Chemistry answer on giant covalent structures, covering the structures of diamond, graphite and silicon dioxide, and how their covalent bonding explains very high melting points, hardness, and why graphite conducts electricity while diamond does not.
- Metallic bonding as positive ions in a sea of delocalised electrons, how this explains the properties of metals, and why alloys are harder than the pure metal.
A CCEA GCSE Chemistry answer on metallic bonding, covering the model of positive ions in a sea of delocalised electrons, how it explains conductivity, malleability and high melting points, and why alloys are harder than the pure metal.
- Electron arrangement in shells for the first 20 elements, writing electron configurations, and the link between outer-shell electrons, the group number and chemical reactivity.
A CCEA GCSE Chemistry answer on electron arrangement, covering how electrons fill shells for the first 20 elements, how to write electron configurations, and how the number of outer-shell electrons links to the group, the period and the chemical reactivity of an element.
- The properties and trends of the Group 1 alkali metals, the Group 7 halogens and the Group 0 noble gases, including reactivity trends and displacement reactions of the halogens.
A CCEA GCSE Chemistry answer on group trends, covering the properties and reactivity of the Group 1 alkali metals, the Group 7 halogens with their displacement reactions, and the unreactive Group 0 noble gases, and explaining each trend in terms of electron arrangement.
Sources & how we know this
- CCEA GCSE Chemistry specification (1110) — CCEA (2017)