Ionic Bonding – GCSE Chemistry Revision (AQA Additional Science – Double and Triple)

Why bond?

• Elements react with other elements because they ‘want’ to end up with a full outer electron shell
• Electrons surround the nucleus of an atom in shells – remember Atomic Structure. The shells go (2,8,8) when full
• Getting the full shell will make them very stable
• The noble gases on the far right of the periodic table are like this – they don’t react with anything very much because they already have full shells
• Atoms can get a full shell by:
• Losing or gaining electrons in ionic bonding
• Sharing electrons in covalent bonding

Ionic:

• Ionic bonding happens between metals and non-metals
• Sodium and Chlorine can react together – they bond ionically to produce sodium chloride (table salt)
• Sodium’s electron shells go (2,8,1) – all its shells are full except the outer one, which only has a single electron in it… if it can get rid of that electron, its new outer shell will be full
• Chlorine’s shells go (2,8,7) – it just needs one more electron; then all its shells will be full
• The solution to this problem is for sodium to give its spare electron to chlorine – then everyone’s happy, so to speak… both atoms are now stable

The Consequences

• However, the balance of charges has been shifted!
• Normally, an atom has an equal amount of protons and electrons
• Electrons are negatively charged, and protons are positively charged, but they cancel each other out meaning the atom is neutral overall
• But this doesn’t happen after ionic bonding
• The sodium atom has sacrificed an electron to gain its outer shell – this means it has more protons than electrons, so the atom now has an overall positive charge
• Likewise, the chlorine atom has gained an electron, so it has more electrons than protons, and it has an overall negative charge

Ions

• The sodium and chlorine atoms have become ions
• An ion is an atom which has lost or gained an electron and thus has a charge
• The sodium is now a positive ion and the chlorine is now a negative ion
• And you know what happens to positives and negatives!
• Opposites attract – the ions get stuck together by their electrostatic charges!
• That’s why they call it ionic bonding

Magnesium and Oxygen

• Magnesium goes (2,8,2) – it needs to get rid of that 2 in its outer shell
• Oxygen goes (2,6) – it needs two more electrons to fill up
• So magnesium donates its two spare electrons to oxygen
• Because magnesium has lost TWO electrons, it now becomes an ion with a positive charge of 2 (because it has two more protons than electrons)
• Oxygen has gained two electrons, so it becomes an ion with a negative charge of two
• They bond together as usual
• Don’t forget that gaining electrons gets you a negative charge
• Losing electrons gets you a positive charge

Potassium and Oxygen

• Potassium’s electron shells go (2,8,8,1) – it really needs to get rid of that ONE pesky electron hogging its outer shell
• As I’ve said, oxygen goes (2,6) – it needs to gain TWO electrons
• So if the potassium gives the oxygen its spare electron it’s happy – it becomes a stable potassium ion with a full outer shell and a single positive charge
• BUT, the oxygen atom is not satisfied – it still needs one more electron to fill up its outer shell
• What are we gonna do?! Well, the solution is to bring in a second potassium atom
• Like its friend was, this new potassium atom is looking to lose one electron
• After gives an electron to oxygen, everything is fine – the two potassium ions both have single positive charges, and the oxygen has become an ion with a full outer shell and a double negative charge
• The three ions stick together – not so much because of their gratitude, but because of the strong electrostatic force that’s now bonding them
• So the moral of the story is, sometimes it takes two atoms to get the right amount of electrons

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