Molecules
Science: KS3, topic 2.3.9
Molecules
Molecules are formed when two or more atoms join together chemically. Different types of bonds form to chemically join different elements.
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Covalent bonds
- Covalent bonds are bonds between non-metals and non-metals.
- Covalent bonding is the sharing of electrons in the outer shell of the atoms.
- Sometimes atoms can share two or three pairs with each other.
- The bonding is strong between covalent bonds.
Molecules
- Molecules are two or more atoms joined together by strong covalent bonds.
- The intermolecular forces between the atoms however are weak.
- Atoms in molecules are always joined together by covalent bonds.
Properties of molecules joined by covalent bonds
- They tend to have low boiling points.
- They tend to have low melting points.
- They are often poor electrical conductors.
- They are often poor thermal conductors.
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Diatomic atoms
- Two atoms covalently bonded together are called diatomic.
- Group 7 atoms will form single bonds (Cl2).
- Group 6 atoms will form double bonds (O2).
- Group 5 atoms will form triple bonds (N2).
Examples of molecules with covalent bonds
- Other examples of molecules include:
- Water H2O
- Hydrochloric Acid HCl
- Carbon Dioxide CO2
- Sulfur Dioxide SO2
Test yourself on Molecules
Which of the following combinations can covalent bonds form between?
What type of bonds do group 6 atoms form?
Why do substances made of covalently bonded molecules usually have low melting and boiling points?
Select the correct statement for each pair
A plastic ruler is made from molecules joined by covalent bonds. Which property would you expect it to have?