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

[Chemist20]

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!

 

[Chemist20]

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.

 

[DrDu]

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.

 

[Chemist20]

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 .. :)

 

[LudusRex]

Your understanding of the trend in metallic radii for transition metals is correct. As you stated, the metallic radii decrease as the period increases, due to the increase in effective nuclear charge (Zeff). This means that the valence electrons are held more tightly by the nucleus, resulting in a smaller atomic radius. This is also known as the lanthanide contraction.

However, it is important to note that the trend in metallic radii is different from the trend in ionic radii. In ionic compounds, the size of the ions is determined by the balance between the attractive force of the opposite charges and the repulsive force of the electron shells. In metallic compounds, the size of the atoms is determined by the strength of the metallic bond, which is a result of the delocalization of electrons in the metal lattice.

In transition metals, the valence electrons are located in the d orbitals, which are closer to the nucleus compared to the s and p orbitals. This means that the electrons are more strongly attracted to the nucleus, resulting in a smaller atomic radius. Additionally, the d orbitals also have a higher energy, making them more easily contracted as the atomic number increases.

In summary, your understanding of the trend in metallic radii is correct. The decrease in radii as the period increases is a result of the increase in effective nuclear charge and the contraction of the d orbitals. It is important to differentiate between the trends in metallic and ionic radii, as they are determined by different factors. I hope this helps to clarify any confusion.