Bonding & structure
Ionic, covalent and metallic bonding, the states of matter, and how the structures explain properties.
Watch the lesson
Every point below, worked through in one video, and each point links straight to its own part.
Learn
Bonding & structure, explained point by point
Everything the GCSE specification expects you to be able to do, and how to actually do it - the same lesson a signed-in student studies from.
Describe ionic bonding and giant ionic lattices
When a metal reacts with a non-metal, electrons transfer: the metal loses electrons to form positive ions and the non-metal gains them to form negative ions. The opposite charges attract strongly in all directions, building a giant regular lattice - like sodium chloride. These strong forces give ionic compounds high melting points.
Describe covalent bonding in simple molecules and giant covalent structures
Non-metal atoms share pairs of electrons to form covalent bonds. In simple molecules like water or CO₂ the bonds within are strong but the forces between molecules are weak, so they melt easily. In giant covalent structures like diamond and graphite, a whole network is bonded together, which makes them very hard with very high melting points.
Describe metallic bonding
In a metal, positive ions sit in a regular arrangement surrounded by a "sea" of delocalised outer electrons free to move. The attraction between the ions and this sea holds the metal together strongly. The free electrons let metals conduct electricity and heat, and the layers can slide, so metals bend rather than shatter.
Describe the three states of matter and changes of state
Particle theory explains states: in a solid particles are packed in fixed positions and only vibrate; in a liquid they touch but can move past each other; in a gas they are far apart and move fast. Heating adds energy to overcome the forces between particles, causing melting and boiling; cooling reverses it. Stronger forces mean higher melting and boiling points.
Explain properties from structure and bonding
A substance's properties come from its structure. Ionic compounds conduct only when molten or dissolved, because then the ions are free to move. Graphite conducts because it has spare delocalised electrons, while diamond does not. Metals conduct and are malleable thanks to their free electrons and sliding layers. Linking property to structure is a favourite exam skill.
Bonding & structure key terms
The words the specification and the mark schemes use, each defined the way an examiner wants it.
- Ionic bond
- The strong electrostatic attraction between oppositely charged ions, formed when a metal transfers electrons to a non-metal.
- Covalent bond
- A shared pair of electrons between two non-metal atoms.
- Metallic bonding
- The attraction between positive metal ions and the sea of delocalised electrons around them.
- Delocalised electrons
- Electrons free to move through a structure rather than staying with one atom. They are why metals and graphite conduct electricity.
- Intermolecular forces
- The weak forces between molecules. They are what is overcome when a simple molecular substance melts or boils, which is why those substances have low melting points.
- Giant covalent structure
- A lattice of atoms all joined by strong covalent bonds, such as diamond, graphite or silicon dioxide. Very high melting points.
- Polymer
- A very large molecule made of many repeating units (monomers) joined by covalent bonds.
- Allotropes
- Different structural forms of the same element, such as diamond, graphite and graphene, which are all carbon.
Common mistakes in Bonding & structure
The slips that cost marks year after year, and what to do instead.
Describing sodium chloride as made of atoms or molecules instead of ions.
An ionic compound is a giant lattice of positive and negative ions, held by strong electrostatic forces acting in all directions. There are no molecules in it, so write about ions and the forces between them.
Saying the covalent bonds break when a simple molecular substance, such as water, melts or boils.
The covalent bonds inside each molecule stay intact. Melting and boiling only overcome the weak intermolecular forces between the molecules, which is why these substances have low melting and boiling points.
Saying solid ionic compounds conduct electricity, or that electrons carry the charge in a molten one.
Ionic compounds conduct only when melted or dissolved in water, because then the ions are free to move and carry the charge. In the solid, the ions are held in fixed positions.
Saying the layers in graphite are held together by weak covalent bonds.
Each carbon forms three covalent bonds within its layer, and there are no covalent bonds between layers, so they slide easily. The fourth outer electron from each carbon is delocalised, which is why graphite conducts.
Saying alloys are harder because their atoms are bonded more strongly.
In a pure metal, the layers of atoms slide over each other easily. An alloy contains atoms of different sizes that distort the layers, so they cannot slide as easily and the metal is harder.
Practice
Try a Bonding & structure question
A GCSE-style original question from this topic. Have a go before you open the working - deciding on an answer first is what makes the working stick.
Solid sodium chloride does not conduct electricity, but molten sodium chloride does. Which statement explains this?
- the solid contains no charged particles at all
- melting splits the ions into neutral atoms that carry the charge
- melting releases delocalised electrons that carry the charge
- in the molten state the ions are free to move and carry charge
Show the answer and the working
Answer: in the molten state the ions are free to move and carry charge
Conduction needs charged particles that can move. The ions exist in both states, but only in the molten liquid are they free to move.
- Electrical conduction needs charged particles that are free to move.
- In solid sodium chloride the ions are held firmly in the lattice, so they cannot move.
- When the compound melts, the lattice breaks up and the ions become free to move.
- The moving ions carry the charge, so the molten compound conducts.