My favourite element is carbon – most life is based on carbon but it can also be really bad for life! Three of the big 5 mass extinctions in earth history are linked to major volcanic eruptions that not only sent toxic sulphur compounds into the atmosphere but also loads of carbon. This then caused the atmosphere to warm up, acidified the oceans and killed lots of plants and animals. This is similar to what is happening today with climate change. Carbon and the carbon cycle fascinate me – too little carbon and there is no life, too much and it can kill so much and cause terrible problems for ecosystems.
Mainly because of hydrogen bonding… which is where groups of hydrogens have forces between them. And that’s the reason why water gets bigger when it turns to ice. And it’s why you can fill your cup with water, and it will go above the height of the cup before spilling over (have paper towels close by if you’re going to try this!).
I am an oxygen kind of person 😉 besides the fact that it is essential to the live in the planet and for us to breath, it is also really interesting how confused we seem to be about it! Is it good or bad? What are the dangers of pure oxygen? Check this really cool article http://www.damninteresting.com/beware-the-dangers-of-oxygen/ !