Will the bond angle in H2O(104.5) increase if water is bind to other molecules?

Hi guys I encounter an Edexcel question asking which complex ions have a bond angle of 107 within them: [CuCl4]2-, or [Cr(H2O)6]2+.

I chose [CuCl4]2- because I thought their bond angle, which is 109.5, is quite close to 107. But apparently the mark scheme says it is [Cr(H2O)6]2+. Since the bond angle between the ligand and the chromium ions are 90 degrees, I think the 107 degrees comes from within the water molecule. But H2O apparently have a bond angle of 104.5 degrees because of the two lone pairs, so I am confused. Does donating one lone pair away (hence making it a bonding pair of electrons) makes the force of repulsion weaker? Is that why the angle between water molecules has increased to 107?

Any answers will be much appreciated, thanks in advance guys!

Reply 1

User135792468

19

Original post by BrowniesMorgan

Hi guys I encounter an Edexcel question asking which complex ions have a bond angle of 107 within them: [CuCl4]2-, or [Cr(H2O)6]2+.

I chose [CuCl4]2- because I thought their bond angle, which is 109.5, is quite close to 107. But apparently the mark scheme says it is [Cr(H2O)6]2+. Since the bond angle between the ligand and the chromium ions are 90 degrees, I think the 107 degrees comes from within the water molecule. But H2O apparently have a bond angle of 104.5 degrees because of the two lone pairs, so I am confused. Does donating one lone pair away (hence making it a bonding pair of electrons) makes the force of repulsion weaker? Is that why the angle between water molecules has increased to 107?

Any answers will be much appreciated, thanks in advance guys!

Depends what you refer to as binding. If you mean weak van der Waals forces and electrostatic attraction to a salt for example then it shouldn’t affect the bond angle and even if it does it would be a very small changes.

However if the lone pairs became bonding pairs then there wouldn’t definitely be a change in the bond angle and shape.

Reply 2

Swingsun

1

Original post by BrowniesMorgan

Hi guys I encounter an Edexcel question asking which complex ions have a bond angle of 107 within them: [CuCl4]2-, or [Cr(H2O)6]2+.
I chose [CuCl4]2- because I thought their bond angle, which is 109.5, is quite close to 107. But apparently the mark scheme says it is [Cr(H2O)6]2+. Since the bond angle between the ligand and the chromium ions are 90 degrees, I think the 107 degrees comes from within the water molecule. But H2O apparently have a bond angle of 104.5 degrees because of the two lone pairs, so I am confused. Does donating one lone pair away (hence making it a bonding pair of electrons) makes the force of repulsion weaker? Is that why the angle between water molecules has increased to 107?
Any answers will be much appreciated, thanks in advance guys!

The water molecules each form a covalent co-ordinate bond with Cr so each water molecule has 3 bonding and one lone pair so bond angle goes from 104.5 to 107 degrees in the water molecule

Will the bond angle in H2O(104.5) increase if water is bind to other molecules?

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