Molecules & Compounds (CIE IGCSE Chemistry)
Revision Note
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Covalent Bonds in Complex Covalent Molecules
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- Some atoms need to share more than one pair of electrons to gain a full outer shell of electrons
- If two adjacent atoms share two pairs of electrons, two covalent bonds are formed, also known as a double bond
- If two adjacent atoms share three pairs of electrons, three covalent bonds are formed, also known as a triple bond
Nitrogen:
- When 2 nitrogen atoms react they share 3 pairs of electrons to form a triple bond
Ethene:
- In ethene, the 2 carbon atoms share 2 pairs of electrons
- This is known as a double bond
Methanol:
Carbon Dioxide:
Exam Tip
Be careful when drawing dot-and-cross diagrams, it is a common mistake for students to draw the wrong type of diagram. Remember, if the compound contains metal and non-metal, it is an ionic compound and you need to draw the ions separated, with square brackets around each ion, together with a charge. If the compound contains non-metal atoms only, it is a covalent compound, the shells should overlap and contain one or more pairs of electrons.
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