Atomic Radii and the Periodic Table

[Kassidy Patron 1L]

Hi! I understand that as you go across a period, the atomic radius decreases and when you go down a group, the atomic radius increases. Usually in problems where we rank the atomic radii, the provided atoms are either in the same group or period. Will there ever be a time where we have to compare radius size when the atoms are in different groups and periods? If we had to compare them, how would we rank them? For example, if we had to compare the atomic radii between nitrogen and sulfur, which is bigger? How could we tell?

[madelyn kelly 1I]

I spoke to a UA about the same issue, and she told me that most of the time we will be given elements from the same column or group to avoid this confusion. If asked to compare two elements that are diagonal, my UA told me that you judge by the vertical trend. In this case, Sulfur would have a larger atomic radius than Nitrogen although they are very close in size.

[LavieTran2B]

Hi,

The previous person was correct in that Sulfur's atomic radius is larger than Nitrogen's. For a more in-depth explanation, it is because sulfur's principal quantum number is larger than nitrogen's and because of that, the outermost shell of sulfur is further away from the nucleus than that of nitrogen's. Hope this helps!

[Marilyn]

Sulfur would have a larger radius because it has one more electron energy shell.

I found this article and chart helpful in understanding this concept. https://www.thoughtco.com/element-size-on-the-periodic-table-608793

Helmenstine, Anne Marie, Ph.D. "Size of the Elements on the Periodic Table." ThoughtCo, Aug. 25, 2020, thoughtco.com/element-size-on-the-periodic-table-608793.

[Claudia Longo 2J]

Hi! I understand that as you go across a period, the atomic radius decreases and when you go down a group, the atomic radius increases. Usually in problems where we rank the atomic radii, the provided atoms are either in the same group or period. Will there ever be a time where we have to compare radius size when the atoms are in different groups and periods? If we had to compare them, how would we rank them? For example, if we had to compare the atomic radii between nitrogen and sulfur, which is bigger? How could we tell?

The best ways to compare radius sizes is to take elements from different groups and periods. Just remember that the biggest atoms tend to be in the bottom left-hand corner of the periodic table. Sulfur is larger than Nitrogen because it is not as far to the right of the periodic table as Nitrogen.
The smallest atoms are usually at the top right-hand corner of the periodic table because atomic radius increases up a group and across a period.

[Brooklyn Burgess 3L]

An increase in the atomic radii of one or more of the bonding atoms generally leads to an increase in bond length.

[elletruchan2I]

Hi Kassidy!
There shouldn't ever be a time where you have to rank atomic radii outside of these definitions, unless it is something drastic enough where it would be an obvious answer (like the far right and left corners of the table).

[cnyland]

Increases to the left and down, and I dont think we will be expected to understand/compare past this.