Which of the following elements has the greatest affinity for electrons? A) N, B) Li, C) F, D) Br, or E) Mg.
N is the symbol for nitrogen, Li is the symbol for lithium, F is the symbol for fluorine, Br is the symbol for bromine, and Mg is the symbol for magnesium. Before we go any further, we need to be clear about what affinity for electrons means. Generally speaking, affinity means like or attraction to. In a chemical context, affinity for electrons means how readily these elements or atoms of these elements attract or accept electrons.
The term that might first come to mind when thinking about accepting electrons and affinity for electrons is electron affinity. Electron affinity is a measure of the energy released or absorbed when an electron is added to an atom or ion. And the other thing you might think of when it comes to attracting electrons is electronegativity. These properties, although correlated to some degree, don’t always match up. But all we need to do is find the element that has the greatest affinity for electrons. So, we need to find just the one at the top.
To help us out, let’s have a look at the periodic table. If we move left to right along a single period, the atomic number of the elements increases. So, the number of protons in their nuclei increases. And therefore, the positive charge of the nuclei increases as well. Now, in the other axis, if we go from the bottom of the group to the top of the group, we’re going to have fewer electron shells, which means the force of attraction between a positive nucleus and the outer electron is going to increase.
These factors combined means that if you move from the bottom left to the top right of the periodic table, generally speaking, elements become more electronegative and have higher electron affinities. By which, I mean more energy is released when we add electrons to them. Of course, we have to make accommodations for the noble gases, which are generally unreactive. Meaning that the element that should come out on top is the one in the top right-hand corner in group 17. And that’s fluorine.
Before putting down our answer fluorine, let’s have a look at exactly where the other elements are. Nitrogen is in the same period as fluorine but is in group 15. So, fluorine has a more positive nucleus, and its outer electrons are in the same shell. So, fluorine should be able to attract electrons more strongly than nitrogen. Lithium is all the way to the left in group one. Still in the same period as fluorine, it’s not going to have anywhere near the same attraction to electrons as fluorine does.
Bromine is two periods below fluorine, so it has two extra electron shells. Even though it has a more positive nucleus, those extra electron shells mean that bromine’s nucleus isn’t able to influence other electrons as fluorine is. And lastly, we have magnesium in group two with one more electron shell than fluorine and not enough protons in the nucleus in order to compensate.
So, based on these trends, fluorine clearly comes out on top. Using the Pauling scale, we can order the elements in order of electronegativity, lithium, magnesium, bromine nitrogen, fluorine. So, the element with the greatest affinity for electrons out of these five is fluorine.