Modelling molecules
Dot and cross diagrams
A dot and cross diagram can model the bonding in a simple A collection of two or more atoms held together by chemical bonds.:
- the outer shell of each The smallest part of an element that can exist. is drawn as a circle
- circles overlap where there is a A bond between atoms formed when atoms share electrons to achieve a full outer shell of electrons.
- Subatomic particle, with a negative charge and a negligible mass relative to protons and neutrons. from one atom are drawn as dots, and electrons from another atom as crosses
For example, a hydrogen molecule forms when a hydrogen atom shares its outer electron with another hydrogen atom.
A dot and cross diagram to model the bonding in hydrogen, H2
Drawing structures
A simple molecule can be modelled by drawing its structure. In these structures:
- show each atom by its A substance made of one type of atom only. symbol
- show each covalent bond as a straight line
For example, a hydrogen molecule has two H atoms and one covalent bond. The diagram shows its structure.
Some examples of models
More guides on this topic
- Formulae and equations - Edexcel
- Hazards and risks - Edexcel
- Atomic structure - Edexcel
- The periodic table - Edexcel
- Ionic compounds - Edexcel
- Giant covalent substances - Edexcel
- Metals and non-metals - Edexcel
- Calculations for all students - Edexcel
- Higher tier only calculations - Edexcel
- Sample exam questions - key concepts in chemistry - Edexcel