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Electronegativity across period 3

Learning outcomes

After studying this page, you should be able to:

  • describe and explain the trend in electronegativity across period 3


The table shows electronegativity values for the elements Na to Ar.

Element Symbol Atomic number Electronegativity
sodium Na 11 0.93
magnesium Mg 12 1.31
aluminium Al 13 1.61
silicon Si 14 1.90
phosphorus P 15 2.19
sulfur S 16 2.58
chlorine Cl 17 3.16
argon Ar 18

Electronegativity is the ability of an atom to attract the bonding electrons in a covalent bond.

The table gives values on the Pauling scale, which have no units. Fluorine (3.98) is the most electronegative element.


Electronegativity in the periodic table

Description of trend

The graph shows how electronegativity varies across period 3:

  • as the atomic number increases, the electronegativity of the elements increases.
When you click on the download symbol, you will be able to download the graph as an image file or pdf file, save its data, annotate it, and print it. Note that graphs will be watermarked.

Explanation of this trend

Going across period 3:

  • the nuclear charge increases …
  • the atomic radius decreases …
  • there are more electrons, but the increase in shielding is negligible because each extra electron enters the same shell …
  • so electrons will be more strongly attracted to the nucleus.

In Period 3, sodium with 11 protons is the least electronegative element, and chlorine with 17 protons is the most electronegative element. You might expect argon (with 18 electrons) to be the most electronegative element in Period 3. However, it does not form covalent bonds, so it does not have an electronegativity value.

Thank you to Ismail Abebanjo from Nigeria for pointing out an error on this page.
It is now corrected!