Atomic radii of halogens

[lemur]

Is there a reason that the atomic radii of the elements in the halogen column of the periodic table are smaller than most other elements?

[mississippichem]

As you move to the right in the p-block, (B, C, N, O, F, Ne...), the every element has one more electron in that p-orbital than the last. Boron has 1, Carbon has 2...so the halogens have 5 electrons in their valence p-orbitals, and p-orbitals can only hold 6 electrons. As we go along that period [row] the nucleus is getting larger so the effective coulombic attraction on those electrons is getting larger, hence the tighter atomic radii. Wikipedia atomic radii; they have a good chart.

[lemur]

As you move to the right in the p-block, (B, C, N, O, F, Ne...), the every element has one more electron in that p-orbital than the last. Boron has 1, Carbon has 2...so the halogens have 5 electrons in their valence p-orbitals, and p-orbitals can only hold 6 electrons. As we go along that period [row] the nucleus is getting larger so the effective coulombic attraction on those electrons is getting larger, hence the tighter atomic radii. Wikipedia atomic radii; they have a good chart.

I looked at the chart, which is where I got the question. So that makes sense about the size and charge of the nucleus growing, but why does the radius suddenly become larger when the shell is full in the noble gas column? Does a full shell somehow have greater resistance to the attraction of the protons? Also, I don't recall the radii increasing significantly from a noble element to the next element with one more proton. Maybe I should go study it again closer, though, because I just recall the general pattern of larger radii as you go down except for the halogens staying small.

 

 

 

[Horza2002]

You also need to be careful on what you are using to define the atomic radii; there are several different methods

• Van der Waals radii - half the minimum distance between the nuclei of two atoms of the element that are not bound to the same molecule
  
• Covalent radii - the radius of an atom when covalently bound to another atom
  
• Metallic radii - the distance between adjacent metal atoms when metal bounding is involved
  
• Ionic radii - the distance between certain ions involved in the bonding of a ionic compound
  

 

Depending on which method you are using to define the atomic radii will greatly affect the result you get. Obviously, noble gases can't use covalent, metallic or ionic radii.

 

As you go down the halogen group, they do get larger as a resulting of filling orbitals further from the nucleus...however, they are still the smallest of that period.