Which Compounds Have Both 2c-2e and 3c-4e Bonds?

[utkarshakash]

Homework Statement

Which of the following compounds contains both 2c-2e bond and 3c-4e bond?
A) Be₂Cl₄ B) B₂Cl₄ C) (SnCl₂)_∞ D) both A and C

The Attempt at a Solution

For 3c-4e bond, there must be 3 atoms present. So correct option should be C but the answer is D.

 

[AGNuke]

Check the structure for Be₂Cl₄. You'll see.

 

[Qube]

By 3c-4e do you mean 3 carbon 4 electron bond?

 

[utkarshakash]

Check the structure for Be₂Cl₄. You'll see.

I'm not sure if I correctly understand the term "3c-4e" but I guess it must have 3 centres. Can you please explain what's that?

 

[AGNuke]

In Be₂Cl₄, the two Be atoms are bridged by two Cl atoms. So, if you consider a Be-Cl-Be bridge, the Cl originally belongs to one of the Be atoms, thus accounting for a bond pair in the bridge. But that Cl atom donates its electron pair to the other Be atom so as to fill its empty orbitals, accounting for the other pair in the bridge.

 

[utkarshakash]

In Be₂Cl₄, the two Be atoms are bridged by two Cl atoms. So, if you consider a Be-Cl-Be bridge, the Cl originally belongs to one of the Be atoms, thus accounting for a bond pair in the bridge. But that Cl atom donates its electron pair to the other Be atom so as to fill its empty orbitals, accounting for the other pair in the bridge.

OK. So why is it called 2c-2e and 3c-4e bond?What do these terms mean in general?

 

[AGNuke]

Bonds are made by electrons, and bonds anchor the "centres". It is just some terminologies people like to come up with. If there are two atoms bonded by 2 electrons (a single bond), it is 2c-2e bond. If the overall bond is connecting 3 atoms and 4 electrons are playing the role of bonding, it is simply 3c-4e bond.

 

[utkarshakash]

Bonds are made by electrons, and bonds anchor the "centres". It is just some terminologies people like to come up with. If there are two atoms bonded by 2 electrons (a single bond), it is 2c-2e bond. If the overall bond is connecting 3 atoms and 4 electrons are playing the role of bonding, it is simply 3c-4e bond.

Thanks for explaining so nicely.