Electronegativity can be thought of as the tendency of an atom to attract electrons. If we take a look at any basic periodic table, realize that the trend for electronegativity is, as we move from left to right, electronegativity will increase. As we move up any group, it will also increase.
Based on this, we’re going to say that fluorine is the most electronegative element on the periodic table with a value of 4.0. We don’t include noble gasses in terms of electronegativity because they already have the perfect number of electrons in their outer shell so they’re not included in this.
We’re going to say that Francium which is on the very far left into the bottom of Group 1A, it has the lowest electronegative value of 0.7. You’re not going to be expected to memorize all of these electronegative values but it’s important that you remember the trend in terms of them. Fluorine is the most electronegative. As we head towards it, electronegativity increases. Also, realize that oxygen would have the second highest electronegative value followed by chlorine.
What’s important about electronegativity is that it can help us with bond polarity. Two elements connected together, from this we can determine what kind of bond we have.
The different definitions for them are if there’s a difference of zero for electronegative values, we’d say that that bond is classified as a pure covalent bond.
For example, here we have Br2. In it, we have two bromines connected to each other. They both have values of 2.8 so if you subtracted them from each other, that would give us our electronegative difference. Basically a pure covalent bond is when you have identical elements connected to one another.
From there, if the electronegative difference is small, meaning it’s from 0.1 to 0.4, we classify it as a nonpolar covalent bond. Great example of this is when you have a carbon single bonded to a hydrogen. Carbon here is 2.5, hydrogen here is 2.1. Depending on the addition that you have, you might see it as 2.1 or 2.2. Either case, it really doesn't matter because it falls within this range. You do the larger electronegative value minus the smaller one and that would give you your difference.
Then you can see that if you have a difference between 0.5 and 1.7, that would be classified as a polar covalent bond. Remember, as we say covalent, covalent just means nonmetals connected together. We go into ionic when the difference between the two elements is greater than 1.7. Ionic is technically just a positive ion which tends to be a metal connected to a negative ion which tends to be a nonmetal.
So remember, electronegativity just tells us the likelihood of an atom attracting electrons towards it. The bigger the difference between two elements and their electronegative values, then the more polar their bond becomes and therefore the more reactive it’ll be later. It’s important to just remember the general trends and then just remember the four different classifications for the types of bond that result from differences in electronegativity. If you’re still having issues in terms of this concept, make sure you go back and take a look at my chapter videos dealing with the whole idea of electronegativity as well as the forces between two elements forming a bond with one another.