Covalent Bonds in Simple Molecules
Chemistry: Cambridge International GCSE Supplement, topic 2.5.4
Covalent Bonds in Simple Molecules
Covalent bonds form when atoms share electrons to make simple molecules like CH3OH, C2H4, O2, CO2, and N2. Dot-and-cross diagrams show these bonds.
What are covalent bonds?
- Covalent bonds form when atoms share pairs of electrons.
- These bonds hold simple molecules together.
- Shared electrons complete atoms' outer shells.
- Atoms like carbon (C), oxygen (O), and nitrogen (N) form covalent bonds in molecules.
Dot-and-Cross diagrams
- Dot-and-cross diagrams show electrons from each atom.
- Dots represent electrons from one atom; crosses from another.
- Shared pairs appear between atom symbols.
- These diagrams help visualise electron sharing in covalent bonds.
Covalent bonds in O2 and N2
- Oxygen (O2) has a double covalent bond, sharing two electron pairs.
- Nitrogen (N2) has a triple covalent bond, sharing three pairs.
- Double and triple bonds make molecules stable but differ in strength and length.
- Dot-and-cross diagrams show these pairs between O and N atoms.
Covalent bonds in CO2 and C2H4
- Carbon dioxide (CO2) has two double bonds between carbon and oxygen.
- Ethene (C2H4) has a double bond between carbon atoms and single bonds to hydrogen.
- Carbon forms four covalent bonds to reach a full outer shell.
- Dot-and-cross diagrams show shared electron pairs clearly.
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Covalent bonds in CH3OH (Methanol)
- Methanol (CH3OH) has single bonds between carbon, hydrogen, and oxygen.
- Oxygen forms two bonds: one with carbon and one with hydrogen.
- Covalent bonds share electrons to form this simple molecule.
- Dot-and-cross diagrams clarify the arrangement of electrons.
Test yourself on Covalent Bonds in Simple Molecules
What does a dot-and-cross diagram use to represent electrons from different atoms?