Now, we're going to be talking about
covalent bonds, which means that the atoms are going to
share electrons. Covalent bonds are very strong bonds. They're very important in biology because they're very stable and because most biological molecules are made with covalent bonds. These biological molecules are then very stable.
let's take Carbon for an example. Carbon has four valence electrons ( look at table 8.6 in your textbook, page 238), so it has the opportunity to form four different covalent bonds. So I can draw the four bonds that carbon can form with hydrogens ( the covalency of Hydrogen is 1 )
like this: