More Lessons for IGCSE Chemistry
A series of free IGCSE Chemistry Activities and Experiments (Cambridge IGCSE Chemistry).
Giant Covalent Molecules: Diamond and silicon dioxide
• Small covalent molecules have low melting and boiling points. This is because they have very weak intermolecular forces.
• Giant covalent molecules have millions of strong covalent bonds.
• Giant covalent molecules are always solids at room temperature. They always have high melting and boiling points.
• Diamond is formed from the element carbon. Each carbon atom forms four strong covalent bonds. They cannot conduct electricity because there are no free electrons to carry electrical charge.
• Silicon dioxide is another example of a giant covalent molecules. It consists of silicon and oxygen atoms.
• Graphite has a high melting and boiling point.
• Graphite is soft and slippery.
• Graphite is an excellent conductor of both electricity and of heat.
• Graphite is formed from the element carbon. Each carbon atom forms three covalent bonds.
• The carbon atoms form hexagonal rings. The hexagonal rings are in layers. There are no covalent bonds between the layers so they can slide.
• Delocalised electrons can move. This means they can conduct thermal energy (heat) and electricity.
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