Looks like a Southern Copperhead (as apposed to the common variety). My only run in with a southern phase was in NC and it was a young one that was very aggressive. He was in the road when I found him and I tried to remove him but he was too aggressive. When I was returning from my walk, he was splattered... apparently he thought he could take on a car tire.
As for rat snakes killing chickens... Only if he thinks he can eat it. They are constrictors so they could kill it not realizing that it's too big to swallow, but it's not likely. I think even a very large rat snake would have a hard time taking down an adult chicken but I did have a king snake (about the same size) try to eat my brother in law. Never bit him but it opened its mouth and tried to eat the back of his neck.
Oh yeah, keep in mind, a decapitated snake can still bite and inject venom (I think old yeller died that way) so always burry the head.