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I know that an atom that an atom is more electronegative as it moves up a group or right on a period (in terms of the periodic table).

So if you have two atom that is diagonally across from each other, which one is more electronegative? Do you prioritize groups or periods when determining electronegativity?

For example: Which is more electronegative - Sulfur, or Bromine?

Finally, does this priority also work for first ionization and atomic radius trends. (in other words, if you prioritize groups when determining electronegativity, do you also prioritize groups when determining the other two periodic table trends?)

My guess is that they would be equal, but I may be wrong.

P.S. I would be most likely to give best answer to the person who answers all my questions as a numbered list.

Mike
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    The easiest thing to do is google for a table of electronegativities. As far as I know, there's no simple rule. Period seems more important, but after the d-elements the group is more important because of the higher charge density of additional protons. More exceptions: noble gases who have a full octet where additional electrons add into a new shell, and transition metals with varying d-electron configurations. Imo best to just reference a table. – Blaise Nov 06 '17 at 18:21

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There's no hard and fast rule. In fact, there's actually no rule per se that states that electronegativity does increase along the periods and decreases down the groups. It's just a general trend, which can be and is broken on occasion. For instance, Zinc, to the right of Copper, has an electronegativity of 1.66, while copper is 1.75, which "breaks" the rule that electronegativity increases along the periods.

As far as which one takes precedence, it's a case by case scenario. In some cases, down one and right one would be very close, like you guessed, as with Scandium (1.20) and Zirconium (1.22). However, if you go over to the non-metals, some of them increase radically in a down-one-right-one scenario (particularly from 3rd period to 4th period, such as Aluminum [1.47] to Germanium [2.02], Phosphorus [2.06] to Selenium [2.48], etc.), while some of them decrease radically (particularly from 2nd to 3rd period and 4th to 5th, such as Boron to Silicon, Oxygen to Chlorine, Arsenic to Tellurium, etc.)

Bottom line: There's no rule. You just have to either learn them by heart or check a periodic table such as this one:

Periodic table

anonymous2
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