The chain may be ok or it may need a link, you can check it by the following test. When you install the chain or a new chain put it on the big ring up front at the crank and the smallest cog or gear in the rear at the cassette and size it so that the rear deraileur arm is as close to straight up an down as it can be, in this configuration all will be good.

Best Of Luck, Ride Safe,
Bill G