When you are using video chat, your computers processor is going for its life.
ie
AntiVirus
Firewall
Video
Audio
Restore
Indexing
Network (Internet)
Chat Program?
No doubt many other things running
Basically your processor is running high with all this, and subsequently warms up.
There are cooling pads you can buy for laptops, or maybe just confirm you have got as many background things turned off as possible.
Just normal video/processor heat occuring