So how does this chemistry occur? Well, the bottom line is that chemistry happens because of electrons. Specifically, those electrons arranged in the outermost shells.  So there can be chemical bonds that form between atoms due to positive and negative charges (opposites attracting). Or chemical bonds can form between atoms when they satisfy valence shells (which are the outermost shells of electrons. So electrons tend to spin around the nucleus in different orbits/energy levels. These shells typically exist with the first level holding 2, then 8 after that. 

So chemistry happens through electron shells being satisfied. This can happen through bonding. There are 3 main types of chemical bonds. ionic bonds are when electrons are transferred from one atom to another. The formation of Sodium Chloride is a great example of ionic bonding. Na donates an electron to Cl and both have their outermost shells satisfied. Covalent bonds share their outermost electrons. The formation of water is through covalent bonding. Two hydrogen elements share their outermost electrons with one oxygen and form H2O. Covalent bonds an extremely strong, as opposed to hydrogen bonds, which are weak bonds formed through hydrogens slight positive charge being attracted and forming weak temporary bonds to negatively charged molecules. Such as that which forms when water molecules stick to each other.