Since noone has covered this yet, I'll give a quick explanation. I'm sure the BA covers this somewhere on the site, so you can also go to the front page and look around for it.

Tides involve the gravitational pull on 3 points: the near side, the middle, and the far side. The gravitational pull also differs between any two of these three points. The near side gets pulled more than the center, and the center gets pulled more than the far side. This latter difference seems like the far side getting pulled from the center, which causes the tidal bulge on that side.

I'm not sure about Mercury, and it's too late to look something up.l