Covalent substances
- Created by: emews
- Created on: 18-11-17 18:08
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- Covalent substances
- A covalent bond forms when two non-metal atoms share a pair of electrons.
- The electrons involved are in the outer shells of the atoms.
- An atom that shares one or more of its electrons will complete its outer shell.
- Covalent bonds are strong - a lot of energy is needed to break them.
- Atoms may form multiple covalent bonds - they share not just one pair of electrons but two or more pairs.
- The number of covalent bonds is equal to eight minus the group number.
- Covalently bonded substances fall into two main types:
- simple molecules
- Simple molecules contain only a few atoms held together by covalent bonds.
- Properties
- Low melting and boiling points - this is because little energy is needed to break the weak intermolecular forces.
- Do not conduct electricity - this is because they do not have any free electrons or an overall electric charge.
- giant covalent structures
- Giant covalent structures contain very many atoms, each joined to adjacent atoms by covalent bonds.
- The atoms are usually arranged into giant regular lattices - extremely strong structures because of the many bonds involved.
- Properties
- Very high melting points – this is because a lot of strong covalent bonds must be broken. Graphite, for example, has a melting point of more than 3,600°C.
- Variable electrical conductivity - diamond does not conduct electricity, whereas graphite contains free electrons so it does conduct electricity. Silicon is a semi-conductor – it is midway between non-conductive and conductive.
- simple molecules
- A covalent bond forms when two non-metal atoms share a pair of electrons.
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