in my notes it says that we count the number of electron pairs to see what the shape of molecule is classed as.
e.g. H2O would actually be classed as tetrahedral, as it has two lone pairs and two bonded pairs.
In the book it says that H2O is actually classed as non-linear.
I have guessed that the shape of molecule is possibly classed by the amount of bonded pairs? not the amount of pairs overall?
also i have presumed that if it has four bonded pairs, the angle will be 109.5
But then if it has three bonded pairs, and then one lone pair, the new angle would then become 107.5 . . . . .
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i think i understand this now . . .
looking at the internet seems that there is the molecular shape and the electronic shape. Both use the same description e.g. trigonal planar, but both may be different depending on the pairs of bonded or lone pairs.
but you use the electronic shape in your calculations.
Hi Lewis,
You seem to have sorted out your queries yourself! In an exam, if you were asked to state the shape of water, both 'bent' and 'tetrahedral' would get the mark.
The reason that 'non-linear' is sometimes applied to water is because it has 2 bonding pairs like linear molecules, but does not form a linear shape because of the lone pairs 'pushing' the bonding pairs closer together.
In terms of bond angles....
4 bonding pairs of electrons = 109.5 degrees.
3 bonding pairs and 1 lone pair = 107 degrees.
2 bonding pairs and 2 lone pairs = 104.5 degrees.
See you next week!
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