OCR GCSE Chemistry Structure
This page covers the following topics:
1. Ionic compounds
2. Giant covalent structures
3. Metals and alloys
Ionic compounds form giant regular crystalline ionic lattices, held together by the strong electrostatic forces of attraction between the oppositely charged ions. Ionic lattices may be presented in 2D or 3D by including formulae of the ions or just the charge of them. Sodium chloride (NaCl) is a common example an ionic lattice and is sometimes called rock salt or table salt.
Ionic bonding is stronger than intermolecular forces in other solids. Therefore, compounds that break ionic bonds when they melt or boil, require much more energy, which results in higher melting or boiling points. In contrast, materials that only break weak intermolecular interactions while melting or boiling, require less energy and have lower melting/boiling points.
If ions from an ionic compound are free to move, a compound can conduct electricity. This is true for molten ionic compounds and ionic compounds’ solutions. Solid ionic compounds do not conduct electricity as their ions cannot move.
Some covalent compounds form giant covalent lattices that are large structures with multiple atoms joined together by covalent bonds. Compounds that form giant covalent structures break strong covalent bonds when they meltThese lattices have exceptionally high melting and boiling points. The layout of the atoms in these structures also determines the physical properties of the compound, ie. hardness, density.
Metals form large structures held together by metallic bonding. Pure metals are usually very soft and malleable, so different metallic elements are mixed to form alloys with preferable properties.
Which giant covalent structure is the hardest naturally occuring substance on Earth?
What is an 'alloy'?
Which of the following conduct(s) electricity?
⋅ molten ice
⋅ molten table salt
⋅ rock salt and water solution
⋅ solid silver iodide precipitate
⋅ iron oxide powder
Why does pure lithium chloride only conduct electricity above its melting point?
Diamonds consist of a giant covalent lattice of carbon atoms. Why can diamonds not conduct electricity?
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