Atoms aren't just glued to each other. They form bonds. There are three types of bonds that hold these atoms together.
They are the ionic bond, the covalent bond, and the hydrogen bond. The first bond we have is the ionic bond and is a bond between ions. An ion is defined as a charged atom.
Back in a previous slide we said that all atoms are electrically neutral. The number of protons equals the number of electrons. Well in ions, electrons have been either lost or gained.
If electrons are gained, the atom assumes an overall negative charge. We call these ions anions. If electrons are lost, then the atom assumes an overall positive charge. We call these ions cations. Whether an atom loses or gains electrons is based on which atom it is.
But we won't worry about that. Table salt involves sodium and chlorine. Sodium has only one electron in the outermost orbital and is very unstable. Chlorine has seven electrons in its outermost orbital and is also considered very unstable. Sodium will give up that one electron and chlorine will take it.
When that happens, the outermost orbital of sodium will disappear. Now both atoms are stable, but they had changed their charge. Sodium is overall positive and chlorine is overall negative.
Do you know why? The covalent bond is our next bond and is usually the strongest bond formed between atoms. The prefix co- means to share, and valent refers to the valence electrons.
Valence electrons are those in the outermost orbital only. There are two types of covalent bonds, polar and nonpolar covalent bonds. Polar, that's an interesting word. If you think of a battery, it has a positive end and a negative end. The Earth has a North Pole and a South Pole.
A magnet is just like the battery. The word polar means something that has different ends. A non-polar covalent bond is where the valence electrons are shared equally between all atoms.
Let's take a look at hydrogen gas. Hydrogen atoms have one valence electron. They need two to be stable. If two hydrogen atoms bond, their outer orbitals will slightly overlap and they will each share one electron to the set and the whole molecule is stable. If you look at each orbital, there are two electrons in each.
This would be called a single nonpolar covalent bond. Oxygen atoms have six valence electrons. They need two more to be stable.
However, if two oxygen atoms bond, they can each share two. So when their outermost orbitals come together, there's a total of four electrons being shared. If you count all of the electrons in each oxygen atom, you'll find there should be 8. Don't worry about the colors of the electrons, only the number is important.
This represents a double non-polar covalent bond, much stronger than the single bond. You'll see hydrogen gas written with a line between each H or two dots between them. The line represents two electrons being shared, or one bond. The two dots show the two electrons. Oxygen is the same way, but there should be two lines, or four dots, between the O's.
If we wrote nitrogen gas, there would be three lines or six dots between the ends. Since there are three lines or six dots, how many bonds are there in nitrogen gas? There should be three bonds or a triple nonpolar covalent bond. Very, very strong. If we look at the flip side of the bond, we have the polar covalent bond.
Remember, polar means the ends are different, like positive and negative. Water is a polar molecule. The image shows water and it looks like a Mickey Mouse head.
Two large ears with the hydrogens. and the big oxygen on the bottom. Each hydrogen is slightly positive and the oxygen is very negative. This means the upper half is positive and the bottom is negative or a polar unit.
But why is this important? For a reaction to take place and use water, the substance being dissolved must also be polar. Salt and sugar easily dissolve in a glass of water. I'm sure you've made salt water and sweet tea. However, if you put oil in the glass, it won't mix.
It just sits on the top and balls up. Oil is considered nonpolar, which means it won't dissolve in water. There will be no reaction. The moral of the story is, if both are polar, you will have a reaction.
If both are nonpolar, you will have a reaction. But if one is polar and the other is non-polar, nothing happens. The last bond we have is the hydrogen bond. It is the weakest bond but can be very strong if there are lots of them.
Hydrogen bonds to almost anything. It has only one valence electron and it wants to be stable. I consider hydrogen the lost dog that follows you home.
It wants to be happy. That's why it's called a hydrogen bond. The shape of DNA and the shape of proteins are all based on the hydrogen bond.
If they break, DNA loses its shape. If they break, the protein will no longer function. The hydrogen bond may be weak, but it is very important in biological systems.