In this video we discuss hydrogen bonds. We cover how do hydrogen bonds form, the different elements that take part in hydrogen bonds, and why doesn't oil and water mix.
What are hydrogen bonds?
An attractive force called a hydrogen bond can exist between certain molecules. These bonds are weaker than ionic or covalent bonds, because it takes less energy to break these types of bonds, however, a large number of these bonds going on can exert a strong force.
Hydrogen bonds are the result of an unequal charge distribution on a molecule, these molecules are said to be polar. If we look at a water molecule, we can see the oxygen atom shares electrons with 2 different hydrogen atoms.
So, in total this molecule has 10 protons, 8 from oxygen and 1 each from the hydrogen atoms, and a total of 10 electrons, 2 shared between the oxygen atom and hydrogen atom number one, 2 shared between the oxygen atom and hydrogen atom number 2, and the other 6 non shared electrons from the oxygen atom.
So, this water molecule is electrically neutral, but it has a partial positive side, the hydrogen side, and a partial negative side, the oxygen side of the molecule. The electrons are not shared equally within the molecule, as they have a higher probability of being found closer to the nucleus of the oxygen atom, giving that end a slightly negative charge. So, the hydrogen atoms end of the molecule will have a slightly positive charge.
These charged ends weakly attach the positive end of one water molecule to the negative end of an adjacent water molecule. When water is in liquid form there a few hydrogen bonds, solid form, many bonds, and when water is steam or gas, there are no bonds, because the molecules are too far apart to form any bonds.
Hydrogen bonds only form between hydrogen atoms that are covalently bonded, or bonds where electrons are being shared and not transferred, to an oxygen, nitrogen or fluorine atom. These bonds make water ideal for the chemistry of life. Hydrogen bonds are also important in the structure of proteins and nucleic acids, which we will cover in later videos.
So, now we know that water molecules are polar, or have slightly positive and slightly negative ends, and in fact, many lipids, or fats and oils, are not polar. So their molecules share electrons equally in their bonds. So, these are nonpolar molecules. This means that when water and oil come together they do not form bonds with one another.
Even when we try to mix them, the water molecules will eventually separate because their polar molecules are attracted to one another and will form hydrogen bonds, separating the water and the nonpolar oil molecules.