The Student Room Group

chemistry - shapes of molecules

in general , how do I tell if something is symmetrical ? and what formations are symmetrical e.g linear
Reply 1
I do AQA and I've been using this
https://chemrevise.files.wordpress.com/2022/01/1.3-revision-guide-bonding-aqa.pdf

Page 4 shows the shapes, granted not all of them are in that table. Most teachers say practising questions that ask you to name the shape or draw them will help you and they're right ig. Memorising the shapes won't hurt and you're gonna have to know the rule of a lone pair decreasing the bond angle by 2.5 degrees.

In regards to symmetry, you wanna draw the shape out and see if it's symmetrical. Hope this helps
Reply 2
Original post by H.dy
I do AQA and I've been using this
https://chemrevise.files.wordpress.com/2022/01/1.3-revision-guide-bonding-aqa.pdf

Page 4 shows the shapes, granted not all of them are in that table. Most teachers say practising questions that ask you to name the shape or draw them will help you and they're right ig. Memorising the shapes won't hurt and you're gonna have to know the rule of a lone pair decreasing the bond angle by 2.5 degrees.

In regards to symmetry, you wanna draw the shape out and see if it's symmetrical. Hope this helps

if I draw it out how will I tell if its symmetrical
Reply 3
Original post by faista0
if I draw it out how will I tell if its symmetrical

Ok, first make sure you know what symmetry is before looking at examples

If you look at the Carbon Dioxide molecule, you can see that when you draw it out it is the same on both sides: a C=O bond on the right and the left.
With the other example you have 2 E/Z isomers (if you haven't learnt them yet you will soon) of But-2-ene. The Cis example is symmetrical as it both carbons in the C=C bond are attached to a H and CH3 in the same position. However, in the Trans one, the CH3 groups aren't in the same position and therefore it's not symmetrical.
Reply 4
If the molecule is symmetrical if you put a small mirror across where you think the plain of symmetry is the reflection should look the same as the non-reflected shape. Whether a molecule is symmetrical will depend largely on the actual molecule. A tetrahedral molecule like methane will have loads and loads of plains of symmetry but if you swap the hydrogen atoms for say F, Cl, Br and iodine atoms then the molecule will no longer be symmetrical.

For some help on shapes try here:

https://science-revision.co.uk/A-level_shapes%20of%20molecules.html
Reply 5
Original post by H.dy
Ok, first make sure you know what symmetry is before looking at examples

If you look at the Carbon Dioxide molecule, you can see that when you draw it out it is the same on both sides: a C=O bond on the right and the left.
With the other example you have 2 E/Z isomers (if you haven't learnt them yet you will soon) of But-2-ene. The Cis example is symmetrical as it both carbons in the C=C bond are attached to a H and CH3 in the same position. However, in the Trans one, the CH3 groups aren't in the same position and therefore it's not symmetrical.

thanks!
Reply 6
Original post by faista0
thanks!

no problem

Quick Reply