Covalent Bonding, Structures and Properties – GCSE Chemistry Revision (AQA Additional Science – Double and Triple)

How does it happen?

  • Like with ionic bonding, this sort of bonding involves atoms filling their outer shells to gain stability
  • However, in covalent bonding atoms share their electrons and don’t lose or gain them – so no ions are produced
  • In order to keep sharing, the atoms have to be near each other – they are bonded!
  • Hydrogen has only one electron. If it can get another it will have an outer shell of two, which is plenty when it’s your only shell
  • Fluorine has an outer shell of 7 electrons. Obviously, it would like another.
  • So hydrogen and fluorine team up to produce hydrogen fluoride, sharing electrons with each other as they go

Advanced Bonding

  • Atoms can form more than one covalent bond at once – for instance, carbon can make four
  • This is because it has four outer shell electrons, and needs to gain another four
  • It can share an electron with a hydrogen atom to get one shared in return
  • If it does this twice, it has six outer shell electrons, and two happy hydrogen molecules bonded to it
  • It still needs two electrons, so it can do something special – it can find another carbon atom, and they can both share two electrons with each other, filling up their outer shells
  • Since two electrons are being shared, this is called a double bond

Diagrams

  • To draw diagrams of covalent bonding, make dot and cross diagrams like you do for ionic bonding, but draw them overlapping, so that the shared electrons are in the shells of both the atoms that need them
  • There is another sort of diagram we can use to represent the complicated arrangement I described above – it involves letters and lines
  • Here’s one for the Carbon and Hydrogen example:

H   H
|    |
C=C
|     |
H  H

  • The lines represent the covalent bonds
  • The double line represents the double bond
  • Two carbon atoms have bonded to two hydrogen atoms each, then double bonded  to each other
  • The chemical formula for that compound would be something like C2H4, because there are two carbon atoms and four hydrogen atoms, but I forget what the compound is called
  • Double bonds are harder to break than single bonds

Simple Covalent Molecules

  • Molecules like the one above are called simple covalent molecules
  • They have low melting and boiling points, so they are often gases at room temperature
  • The bonds between the atoms (shared electrons) are strong, but the bonds between the separate molecules are weak, so one of the molecules in the diagram above won’t stick to an identical one

Giant Covalent Structures

  • Some covalent compounds form giant structures similar to the ionic lattices
  • These strong bonds between atoms make them hard with high melting points
  • Carbon atoms in a giant covalent structure make diamond – one of the hardest things on earth, because each atom makes four bonds
  • Diamond, Graphite and Fullerenes are other giant covalent structures, but I won’t go into that here
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About Matt

I like writing, filmmaking, programming and gaming, and prefer creating media to consuming it. On the topic of consumption, I'm also a big fan of eating.
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