Electronegativity is a description of an atom’s tendency to attract electrons to itself. Electronegativity is affected by the atom’s atomic number and by the distance of its bond forming electrons, or valance electrons, from its nucleus. The concept of electronegativity is strongly related to that of ionization energy, or the amount of energy it takes to strip an atom of a valence electron, because a highly electronegative element strongly holds onto it’s electrons. Atoms that tend to donate electrons, by this reasoning, have low electronegativity values.
If there is a bond between two identical atoms, you will then have a bond, of course, between two atoms of equal electronegativity. Thus, the shared pair of electrons that form the bond between two hydrogen atoms, will, on average, be located equidistantly from either nucleus. Similarly, if two atoms of unequal electronegativity are bonded, the electron pair will orbit closer to the atom of greater electronegativity.
How to Read an Electronegativity Chart
When looking across the periodic table of the elements, there are definite patterns of electronegativity that can be observed. As you go from left to right, electronegativity increases, and as you go from top to bottom electronegativity decreases. In this sense, the periodic table itself can possibly be thought of as an Electronegativity Chart.
The scale invented by Linus Pauling is the most commonly used measure for electronegativity. The most electronegative element is fluorine, with an electronegativity of 4.0. The least electronegative element is francium, whose electronegativity is 0.7.
A very interesting way to demonstrate this in an Electronegativity Chart is to plot the atomic numbers of all the elements on the “X” axis of a graph against the Pauling Scale value of an element on the “Y” axis of the graph. We will see the value of electronegativity rise step by step until fluorine’s value of 4.0, corresponding to what was mentioned about electronegativity increasing as we go from left to right across the periodic table. Fluorine is at the top, right edge of the periodic table, so this is what we’d expect.
Then, we move all the way to the right of the periodic table and one row lower to the element with an atomic number of 11, which is sodium, the Pauling value plunges. This, too, is what we’d expect, as we’ve moved lower and to the left, as opposed to higher and rightward. Again, the Pauling value increases as we go from left to right on this row, culminating with chlorine. Chlorine’s value for electronegativity, is also, as expected, lower than that of fluorine, because it is one level lower.
This pattern repeats itself as we chart electronegativity numbers on our Electronegativity Chart.