Chemistry... you've either got it or you don't. That is true. However as we've seen in many of the relationships formed in Grey's it is not chemistry that binds a couple together till death do us part, as was obvious in Cristina Yang and Burke's case. You can ooze that chemical reaction, that spark between you that is so hot you can almost feel the electricity moving between you, but in the end chemistry fades and all the other stuff in between remains.

Physical Attraction, Chemical Reaction was all about what makes us tick on a physical level. While Izzie and George continue to amp up their sex life (well try to get one at least), Mark falls head over for Dr Erica Hahn because she is a wiz in the OR and does not fall for his good looks and boyish charms.

It's all about the bonds that bind us. How some things are immediate and others just take their time to form. As is the case with Izzie and George. They have the love thing, they are best friends, but that raw chemistry between them is not coming alive, as much as they want it to. Are they just trying to find something that is not there? Maybe it's something that a little bit of time and patience will ignite. Can we create a chemical reaction? It's either there or it's not. But we can form a partnership that builds over time in to something amazing and hot, even if it wasn't blindingly obvious in the first place, with a little bit of work.  

Meredith and Derek's chemistry is overflowing. They meet in the lift and their chemistry heats up the TV screen! They've had it right from the word go. But they just can't seem to make it fit in with all the other stuff going on in their lives. Derek's ready, but Meredith can't take that final step towards him. They are meant to be together, but fear keeps standing in their way. Fear of commitment. Fear of surrendering everything to love and losing control. Izzie and George have no fear of that, they've conquered it, but can they conquer the chemistry thing?

Cristina Yang and Burke were sizzling in the OR together. But that didn't get them down the aisle in the end. Izzie and Danny had it definitely, but his heart couldn't take it. Alex has it with everyone but can't seem to make a relationship out of any of it. Mark and Addison were definately hot in the chemistry stakes, but his meandering appetite couldn't keep him in one place for long. And so on and so on and son on. So is it chemistry that binds us? George and Izzie are having trouble with their chemistry right now, but they could outlive even the hottest relationship in Seattle Grace.

What do you think? Who would you vote for as the hottest couple to grace the screen in Seattle Grace? Check out our poll and let us know what you think.