Cl as an Expanded Octet

[Andy Liao 1B]

I remember hearing in lecture that Cl can form an expanded octet. However, I was told that this wasn't possible. Can someone explain or give an example of when Cl forms an expanded octet?

[Gurpreet Khamba 1J]

Since Cl is in the 3rd period, and at the end, is more likely to gain e-, it is possible for it to take electrons if needed. An example of this is ClF3.
There are 28 e- and F will not take more than 8 leaving Cl with an extra 4 e-.

[Tasnia Haider 1E]

Since Chlorine is in the n=3 shell, that means it can gain more electrons to put into a 3d shell, if necessary.

[Yizhou Liu 3L]

ClO4^1- is a good example that Cl has expanded valence shell. If you put Cl as the central atom and connect it with O using single bond, you'll see the formal charge of Cl is +3 and O is -1. However, if you consider it as three double bonds and one single bond, the formal charge of Cl will be 0 and it'll be more stable. In this case, Cl has expanded its valence shell to 14 electrons.