Water + Hydrogen
Posted: Fri Aug 02, 2013 5:02 pm
Why is it that oxygen which is a light molecule becomes heavier when you add two hydrogen molecules? I am confussed by this.
Hi Cora,
When you look at the numbers under the elements on the periodic table, you see that the mass of oxygen is 16. Compared to say, lead, which has a mass of 207.2, oxygen is a pretty light element. On the other hand, look at the mass of hydrogen. It's the lightest of all elements at just 1.008. Oxygen is a lot heavier than hydrogen. Whenever you combine atoms into a compound, and in this case it's water, you add up all the elements in the chemical formula. Since the chemical formula of water is H2O, you add the mass of two hydrogens and one oxygen. 2(1.008) + 16 = 18.016. Therefore, even though there's two hydrogens, oxygen still makes up a big part of water.