I had to change my gmail password, and now my mac won't recognize it or allow me to change it

My gmail got hacked, so I had to change my password. Did so through google, and now I can receive emails on my macbook pro, but I can't send them, and I can't reconcile my passwords- the mac OS won't let me change it. What am I doing wrong. 13 inch Macbook pro retina mid 2014 os X yosemite