4.1 Lone pairs

[Jessica Wakefield 1H]

Indicate whether there must be, may be, or cannot be one or more lone pairs of electrons on the central atom:

0--0--0 linear structure with 180 degree bond angles----> may have one or more lone pairs

can anyone explain to me why it is possible that it could have lone pairs? I had assumed that would make the structure no longer linear and would result in a structure more like part a with 120 degree bond angles.

[Ashley Chipoletti 1I]

If the central atom had 3 lone pairs, and two bonds, the molecule will appear linear.

[Gianna Apoderado 1B]

Here is a diagram clarifying what Ashley said above! You can see that the 3 lone pairs and their electron "clouds" have repulsion, such that the bonds between the central atom and the two other atoms are manipulated to a linear shape.

[Morgan Baxter 1E]

Yes, Gianna's diagram is really helpful. There are two instances where the shape is linear:
1. 2 areas of electron density where none of which are lone pairs
or
2. 5 regions of electron density where three of which are lone pairs

[Swetha Sundaram 1E]

But in part b, there are two areas of electron density and it's linear so I thought that there wouldn't be any lone pairs. But the answer says that there may be lone pairs.

[Alissa Stanley 3G]

In the second diagram posted above, can someone please explain the significance of the thicker line and the dotted line?

[Leanne Wong 1H]

In the second diagram posted above, can someone please explain the significance of the thicker line and the dotted line?

The thicker line indicates that the bond is towards us and the dotted line shows that the bond is going away from us. This is to help represent the 3D shape of the molecule which is more informative than just a 2D shape of the molecule.