Bonding and structure - ionic, covalent and metallic
Students need to learn to represent the electronic structure of elements in dot and cross form and this requires practise to become confident. Some students will have heard that the third shell can hold up to 18 electrons but this complication does not arise until we get to element 20 which is as far as we go at GCSE. This then leads to ionic bonding between metals and non-metals, and covalent bonding between non-metal elements. Students will often fail to recognise whether a compound is ionic or covalent and consequently use the wrong approach in an exam
Students often find bonding in solid structures difficult. Students are expected to be able to explain the macroscopic properties of a substance (melting point, hardness, electrical conductivity) from an understanding of the microscopic structure. It can be useful here for students to ask two questions:
- what are the particles that make up the solid lattice?
- what are the forces between the particles that hold the lattice together?
From the answers to these two questions the macroscopic properties follow.
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