We're going to say that the difference in electronegativity between two elements can determine the type of chemical bond present. We're going to say the greater the difference in electronegativity, the greater the polarity of the bond.
Now, if we take a look, we can see here that we have differences in electronegativities. If the difference is zero, that must mean they both have the same electronegativity value. We classify this as a pure covalent bond. A great example is two bromines bonded together. They're sharing these electrons here in the center, and they're sharing them equally. So, you have these equal arrows between them here. This shading represents their electron cloud; they're equal in size because again, their electronegativity values are the same. They're sharing them perfectly.
Now, once you start getting a little difference in electronegativity, we go into what we call a nonpolar covalent bond. Here, it has a difference between 0.1 and 0.4. If we take a look here, carbon is slightly bigger in terms of its electron cloud because its electronegativity value is a little bit higher than hydrogen's, it's 2.5 versus hydrogen's 2.1. We still have arrows, but notice that this arrow is slightly larger because the electrons belong a little bit more towards carbon's side.
Now, what you need to realize here is that pure covalent is when there is no difference in electronegativity. But it is also classified as being nonpolar.
Intermediate is when the differences are between 0.5 and 1.7. Here, we classify this as a polar covalent bond. If we take a look here, we have chlorine and hydrogen. Remember, once we're greater than 0.4 difference in electronegativity, that's significant. That means we're going to be polar and with a polarity involved, we have dipole arrows. The dipole arrow always points towards the more electronegative element. It's pointing towards chlorine, which is more electronegative than hydrogen. Remember, chlorine is 3.0, hydrogen is just 2.1. With the dipole arrow, we have charges involved, in this case, partial charges. Chlorine will be partially negative, hydrogen will be partially positive.
Finally, if it's larger than 1.7, then it is an ionic bond. Remember, ionic bonds are bonds between a positive ion and a negative ion. Here, the difference is so large that the cation is formed because sodium actually hands over its electron to chlorine. Now here, it also has a dipole arrow, but it's much larger because the polarity is even greater here. This is another difference here; whereas, in polar covalent, we have partial charges, in ionic, we have full charges, so this is fully negative, and this is fully positive. And again, the arrow points towards the more electronegative element. So, just remember, the greater difference in electronegativity, the greater the polarity of the bond. These differences in polarity help to classify different types of chemical bonds present.