How do atoms bond, and how does bonding explain the properties of substances?
Ionic bonding as the transfer of electrons, covalent bonding as the sharing of electrons, metallic bonding as ions in a sea of delocalised electrons, drawing dot-and-cross diagrams, and how each type of structure explains properties.
A focused CCEA GCSE Double Award Science (Chemistry Unit C1) answer on chemical bonding, covering ionic bonding by electron transfer, covalent bonding by sharing, metallic bonding, dot-and-cross diagrams, and how each structure explains the properties of substances.
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 Double Award wants the three types of bonding - ionic (transfer), covalent (sharing) and metallic (sea of electrons) - how to draw dot-and-cross diagrams, and how each structure explains the properties of a substance. Linking structure to properties is the high-mark skill.
Ionic bonding
Ionic compounds form a giant ionic lattice, a regular 3D arrangement of ions. In a dot-and-cross diagram for sodium chloride, sodium loses its single outer electron to chlorine, giving a Na+ ion and a Cl- ion.
Properties: high melting and boiling points (many strong forces to break); conduct electricity when molten or dissolved (ions free to move) but not when solid (ions fixed).
Covalent bonding
Covalent substances can be simple molecules (such as water, H2O, or methane, CH4). In a dot-and-cross diagram, the shared electrons sit between the atoms. Simple molecular substances have low melting points because the forces between molecules are weak (only the strong bonds inside the molecule are hard to break), and they do not conduct electricity because there are no free charges.
Metallic bonding
Properties: metals conduct electricity because the delocalised electrons move and carry charge; they are malleable (can be bent and shaped) because the layers of ions slide over each other without breaking the bonding. Alloys (mixtures of metals) are harder because different-sized atoms distort the layers, stopping them sliding.
Examples in context
Example 1. Why salt dissolves and conducts. When sodium chloride dissolves in water, the lattice breaks up and the ions become free to move. The solution then conducts electricity, which is why salty water conducts but solid salt does not. Structure explains both facts.
Example 2. Why copper is used in wiring. Copper has delocalised electrons that move freely, so it conducts electricity well, and it is malleable so it can be drawn into wires. Metallic bonding explains both properties at once.
Try this
Q1. What type of bonding involves the sharing of electrons? [1 mark]
- Cue. Covalent bonding.
Q2. Why do metals conduct electricity? [1 mark]
- Cue. Their delocalised electrons are free to move and 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-style4 marksExplain why sodium chloride has a high melting point and conducts electricity when molten but not when solid.Show worked answer →
Link the giant ionic structure to the properties for four marks.
Sodium chloride has a giant lattice of oppositely charged ions held by strong electrostatic forces.
A lot of energy is needed to break these many strong forces, so the melting point is high.
When solid, the ions are fixed and cannot move, so it does not conduct.
When molten, the ions are free to move and carry charge, so it conducts. Markers reward strong forces for the high melting point and free-moving ions for conduction when molten.
CCEA-style3 marksExplain why metals are good conductors of electricity and can be bent into shape.Show worked answer →
Use the metallic structure for three marks.
Metals have a lattice of positive ions in a sea of delocalised electrons.
The delocalised electrons are free to move and carry charge, so metals conduct electricity.
The layers of ions can slide over each other without breaking the bonding, so metals are malleable. Markers want delocalised electrons for conduction and sliding layers for being bendable.
Related dot points
- Electron arrangement in shells for the first 20 elements, the link between outer electrons, group number and reactivity, and the modern organisation of the Periodic Table by atomic number into periods and groups with metals and non-metals.
A focused CCEA GCSE Double Award Science (Chemistry Unit C1) answer on the Periodic Table and electron arrangement, covering electron shells for the first 20 elements, the link between outer electrons, group number and reactivity, and the organisation of the table into periods and groups.
- The structure of the atom in terms of protons, neutrons and electrons, their relative charges and masses, atomic number and mass number, isotopes, and calculating relative atomic mass from isotopic abundances.
A focused CCEA GCSE Double Award Science (Chemistry Unit C1) answer on atomic structure, covering protons, neutrons and electrons with their charges and masses, atomic number and mass number, isotopes, and calculating relative atomic mass from isotopic abundances.
- The properties and reactivity trends of the Group 1 alkali metals, the Group 7 halogens including displacement reactions, and the Group 0 noble gases, and how these trends link to electron arrangement.
A focused CCEA GCSE Double Award Science (Chemistry Unit C1) answer on the groups of the Periodic Table, covering the Group 1 alkali metals, the Group 7 halogens and their displacement reactions, the Group 0 noble gases, and how the reactivity trends link to electron arrangement.
- Elements, compounds and mixtures, the difference between physical and chemical change, and the separation techniques of filtration, crystallisation, simple and fractional distillation, and chromatography.
A focused CCEA GCSE Double Award Science (Chemistry Unit C1) answer on elements, compounds and mixtures, covering the difference between physical and chemical change, and the separation techniques of filtration, crystallisation, distillation and chromatography.
- Writing chemical formulae, constructing word and balanced symbol equations with state symbols, relative formula mass, the mole, the relationship between moles, mass and relative formula mass, and using balanced equations to calculate reacting masses.
A focused CCEA GCSE Double Award Science (Chemistry Unit C1) answer on chemical equations and the mole, covering writing formulae and balanced symbol equations with state symbols, relative formula mass, the mole, and using equations to calculate reacting masses.
Sources & how we know this
- CCEA GCSE Science Double Award specification — CCEA (2017)