Why do atomic radii increase as you move down a column in the periodic table?

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Discussion Overview

The discussion centers on the behavior of atomic radii as one moves down a column in the periodic table, exploring the relationships between atomic radius, atomic number (Z), and electron configuration. Participants seek to understand the underlying chemical and physical principles that govern these trends.

Discussion Character

  • Exploratory
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • One participant states that the atomic radius of a cation is less than that of a neutral atom, which is less than that of an anion, and questions the validity of this relationship.
  • Another participant suggests that moving down a column in the periodic table results in the addition of new electron shells, which increases atomic radius.
  • Concerns are raised about the claim that if the atomic number (Z) of one element is less than that of another, the radius of the first element must be greater, with a participant arguing that this is not universally true.
  • Specific examples are provided, such as the atomic radii of sodium (Na), strontium (Sr), and potassium (K), to illustrate that atomic radius does not consistently correlate with atomic number.
  • One participant questions whether there is confusion between atomic number and atomic weight in the context of atomic radii.
  • Links to external articles are shared to provide additional context and graphical representations of atomic radius trends.

Areas of Agreement / Disagreement

Participants express disagreement regarding the relationship between atomic number and atomic radius, indicating that multiple competing views remain on the topic. There is no consensus on the validity of the initial claims about atomic radii.

Contextual Notes

The discussion highlights limitations in the understanding of atomic radius trends, including potential confusion between atomic number and atomic weight, as well as the need for clarification on the categorization of atomic radii across different elements.

M. next
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About the atomic radius,
as a starter it was mentioned (and correct me if am wrong) that:
Rcation < Ratom< Ranion (And we'll know the size of the atom based on these)
Then it was mentioned that: Radius of atom of a certain element increase if we walk straight downwards along a column in the periodic table.
And afterwards: if Z of any element is less than Z of any other one
then the radius of the first is greater than the 2nd.

How come? I really don't get it?
Any chemical, physical explanation (most importantly to the 3rd pt)
 
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cant say for these rules are alway true, if you consider H then removing its electron will leave just a nucleus so rcation<ratom but adding an electron to H it seems the radius would remain the same since the electron would be in the same orbital and shell.

Moving down a given column in the periodic table, you'd be adding many electrons to the next lower element so that new shells would be added increasing the radius of the atom.

For the last pt are you confusing Z with atomic weight?

Here's a brief article on it with a graph. The author says that when a new shell is added the radius clearly jumps up but as electrons are added the shell goes down due to increased attraction to the protons in the nucleus.

http://mmsphyschem.com/atmRad.htm

and here's another wiki article on it that describes things better:

http://en.wikipedia.org/wiki/Atomic_radius
 
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Hello there, jedishrfu
Thanks, I ll be reading them.
But about the 3 points I mentioned, what do you think? Are they all logical?
 
M. next said:
if Z of any element is less than Z of any other one then the radius of the first is greater than the 2nd

Clearly not true. Atomic radius is not a monotonic function of Z. Radius of 11Na 180 pm, of 38Sr 200 pm, of 19K is 220 pm.

It may be true if not ALL elements are taken into account, but just some subset of the periodic table.
 
Hmm.. That's why I was wondering, it doesn't even make sense..
If it so, Borek, how should I categorize radii?
 
Thanks
 

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