Water is an example of a molecule. There is no “water atom”. Water is made of multiple atoms hooked together.
We are imagining that atoms are like lego blocks of different shapes and sizes. We are going to skip a few fundamental things here to get right to the point of making molecules. If I have a lego atom that has 2 empty holes and I have a lego atom that has 2 unused pegs (the bumps that stick out), then I can click them together right? It is sort of the same thing with atoms. They have something called Valence Electrons that are sort of like these holes and pegs. Have you ever heard water called H2O? If so, have you ever wondered why? Well, let’s say you have one big lego with 2 holes and two small legos with one peg each. You could click one of the small legos into one hole on the big lego and the other small lego into the other hole on the big lego. This is now a molecule… more than one atom connected to another. Let’s give the big lego the code “O” and let’s give the two smaller legos the code “H”. When we click them together, we now have 2 H’s and 1 O. One way to write that is “H2O”. The little 2 after the H says we have 2 H legos and the O without any numbers means we just have 1 “O” lego. You could write this as H2O1 but the 1 is just assumed if there is no number there. What we call water is just two H atoms where H stands for Hydrogen and one “O” atom where O stands for Oxygen.
One very interesting thing about the water molecule is how it shares it’s electrons. If you look at the animation on the left, you can see the the electrons spend more time with Oxygen than they do with Hydrogren. This makes water molecules act like tiny magnets. Find more information in “A bucket full of magnets“.
Why does Oxygen want 2 more electrons in it outer shell and why does Hydrogren want two electrons..? Well, you can think of these shells are different levels where the electrons orbit the nucleus (the protons and neutrons). I have done some research that talks about lower energy levels being required when each orbit has a certian number of electrons and different spins, etc. but to be honest, I have never seen a great simplified explination… I will keep looking. If anyone can help, please email me.