Why Does Metallic Radius Decrease Across a Period in Transition Metals?

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Discussion Overview

The discussion centers around the trend of metallic radii in transition metals across a period, specifically addressing the reasons behind the observed decrease in metallic radius as one moves from left to right across a period. Participants explore the definitions and implications of metallic versus ionic radii, as well as the effects of orbital contraction and bonding strength.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Technical explanation

Main Points Raised

  • Some participants assert that the decrease in metallic radius is due to an increase in effective nuclear charge (Zeff), while others challenge this interpretation, suggesting that the relationship between bonding and radius is more complex.
  • There is a contention regarding the definition of metallic radius, with some emphasizing that it is based on the distance between two metal atoms in a bond, while others argue that this should not be conflated with ionic radius considerations.
  • One participant questions the assumption that more contracted orbitals lead to less bonding, proposing instead that contracted orbitals may enhance bonding strength.
  • Another participant raises a question about the trend of increasing metallic radius down a group, suggesting that greater overlap between atoms should lead to smaller radii, indicating a potential misunderstanding of the factors at play.

Areas of Agreement / Disagreement

Participants express differing views on the relationship between metallic radius, bonding strength, and orbital contraction. There is no consensus on the reasons behind the trends observed in metallic radii, and multiple competing interpretations remain unresolved.

Contextual Notes

Limitations in the discussion include varying definitions of metallic and ionic radii, assumptions about bonding characteristics, and the complexity of orbital interactions that are not fully explored.

Chemist20
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I am so confussed..

Talking about transition metals, in the book it says that the general trend in a period is for the metallic radii to decrease due to increase of Zeff. But I don't think this makes sense.

I think: we are talking about metallic radii not IONIC! If its metallic, then the radii would be half the distance between the two metals. hence, the greater bonding, the smaller de radii. Hence, as the period goes by and the orbitals become more contracted, less bonding, GREATER RADII!

why am i wrong?
please help!
 
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Well that's the thing!
metallic radius is defined as half of the distance between two metals in a metal bond.
ionic radius on the other hand is different. that's why i think that talking about zeff should be to explain the ionic radius not the metallic radius.

metallic radius has to be related to the strenght of the m-m bond.
 
Why do you think that more contracted orbitals are less bonding? It is the other way round!
Furthermore, at least main group metals are well described as ionic cores surrounded by nearly free conduction electrons, the distance of the atoms being dictated by the radii of the ionic cores.
 
DrDu said:
Why do you think that more contracted orbitals are less bonding? It is the other way round!
Furthermore, at least main group metals are well described as ionic cores surrounded by nearly free conduction electrons, the distance of the atoms being dictated by the radii of the ionic cores.

oh god yes.. hadn't realized the first part :)
okay, but then, why does the metallic radius increase as the group goes down? as the group goes down the overlap between metals is greater and hence should be a smaller metallic radii!

didn't quite get the last part of your comment .. :)
 

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