Which of the following period-three elements has the highest electronegativity? A) Cl, B) Si, C) Al, D) Na, or E) Ar.
That’s chlorine, silicon, aluminum, sodium and argon. Period three refers to a row on the periodic table. Specifically, this row, which contains our five candidate elements, left to right, sodium, aluminum, silicon, chlorine and argon. Electronegativity is a measure of the strength of attraction to electrons in bonds for an atom. The most common scale for electronegativity is the Pauling scale, where elements are placed on the scale between zero and four. A high value indicates strong attraction to electrons in bonds. While a low value indicates a weak one.
With elements arranged in the periodic table, the general trend is that electronegativity increases left to right and bottom to top. On this basis alone, argon should be our answer. Since it’s placed most to the right. However, argon is a noble gas. And it is generally considered to be unreactive. So argon does not have a defined electronegativity value.
So our next most viable candidate is chlorine. Chlorine is furthest to the right of all our remaining candidates. Therefore, based on the trend of electronegativity values on the periodic table, chlorine is our answer. Chlorine readily forms bonds, so it has a valid electronegativity value. Therefore, of the five elements given, the one with the highest electronegativity value is chlorine.
Another way to demonstrate this is to look at the actual electronegativity values of each element. Chlorine has a value of 3.16, silicon 1.90, aluminum 1.61, sodium 0.93, and argon does not have a defined electronegativity value.