In this video we're going to begin our lesson on covalent bonds. Covalent bonds are defined as an interaction between two atoms that results from the sharing of electrons. In this context, the word covalent simply means the sharing of electrons. If electrons are being shared between two different atoms, then we have ourselves a covalent bond. Electrons that are being shared between atoms can be shared in two different ways. This leads to two different types of covalent bonds that share the electrons in different ways. The first type of covalent bond that you all should know is the nonpolar covalent bond, and the second type of covalent bond is the polar covalent bond. Later in our course in a different video, we'll talk more about the differences between nonpolar covalent bonds and polar covalent bonds, but for now, what I want you to know is that the existence of these two types of covalent bonds is due to differences in atoms' electronegativities.
Electronegativity is defined as a measure of an atom's attraction to electrons, or in other words, it's a measure of how hard atoms pull on electrons. Electronegativity is scaled from 0 all the way up to 4 at its maximum. An electronegativity of 0 means that an atom is not very electronegative at all, which means that it does not pull hard on electrons. An electronegativity value closer to 4 means that the atom is very electronegative and that it pulls really hard on electrons. When you look at a periodic table, you'll notice that the atoms are arranged based on their electronegativity values. As we go from the left-hand side to the right-hand side of the periodic table, there are increasing values of electronegativities. You can see these numbers underneath, representing the electronegativity values of these atoms.
As you start from the left and make your way to the right, atoms become more electronegative. Notice also that atoms increase in electronegativity from bottom to top. So if you pick any column, notice if you start at the bottom and make your way to the top, the atoms become more and more electronegative. It's important to note that electronegativity is the reason for these two different types of covalent bonds. There's no need to memorize all these electronegativity values, but you should be able to recognize that oxygen is one of the most electronegative atoms that exist. The only atom that is more electronegative than an oxygen atom is fluorine. This is important to keep in mind especially when we start to talk about the water molecule later in our course, which we know has one oxygen atom. Oxygen is very electronegative and it pulls really hard on electrons for that reason.
This concludes our introduction to covalent bonds and moving forward in our course, we'll talk more about nonpolar and polar covalent bonds. I'll see you all in our next video.