Chem Question

[TheRealAngeleno]

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Which of the following species is MOST likely to exhibit color?

A. ZnCl2
B. TiO2
C. CrCl3
D. BF3

I was wondering if someone could please explain this concept and how a species could exhibit color. Thanks.

 

[Mcat35]

Which of the following species is MOST likely to exhibit color?

A. ZnCl2
B. TiO2
C. CrCl3
D. BF3

I was wondering if someone could please explain this concept and how a species could exhibit color. Thanks.

Between CrCl3 and ZnCl2 I would pick CrCl3 since it has more empty D orbitals than ZnCl2. When you see these color questions think transition metals.

here is a explanation I found online for why. I just knew empty d orbital transition metals can form color complexes lol...


When the d-level is not completely filled, it is possible to promote and electron from a lower energy d-orbital to a higher energy d-orbital by absorption of a photon of electromagnetic radiation having an appropriate energy. Electromagnetic radiations in the visible region of the spectrum often possess the appropriate energy for such transitions.

 

[flodhi1]

Which of the following species is MOST likely to exhibit color?

A. ZnCl2
B. TiO2
C. CrCl3
D. BF3

I was wondering if someone could please explain this concept and how a species could exhibit color. Thanks.

Well B is out of the way it's not even a metal. So carrying on
Outer configuration of
Cr is 4s^1 3d^5
Zn is 3d^10 4s^2.
Ti is 4s^2 3d^2
Therefore the d orbitals of Chromium are empty compared to Zinc. Now my understanding goes something like this. Electrons in alkali metals and transition metals that have d orbitals have their excited electrons drop from excited state to ground state. An element emits light when electrons in higher energy levels drop to lower levels. Since the energy levels are quantized, the photon energy emitted by transition metals are also quantized. So light of only a specific wave length from each element is emitted. This all goes down to the basis of atomic phonemonon / Photoelectric effect and Bohrs model concerning electrons. Just nail down the two concepts of absorption of energy jumps to excited orbital and emission of energy occurs when "unexcited".

 

[Mcat35]

Well B is out of the way it's not even a metal. So carrying on
Outer configuration of
Cr is 4s^1 3d^5
Zn is 3d^10 4s^2.
Ti is 4s^2 3d^2
Therefore the d orbitals of Chromium are empty compared to Zinc. Now my understanding goes something like this. Electrons in alkali metals and transition metals that have d orbitals have their excited electrons drop from excited state to ground state. An element emits light when electrons in higher energy levels drop to lower levels. Since the energy levels are quantized, the photon energy emitted by transition metals are also quantized. So light of only a specific wave length from each element is emitted. This all goes down to the basis of atomic phonemonon / Photoelectric effect and Bohrs model concerning electrons. Just nail down the two concepts of absorption of energy jumps to excited orbital and emission of energy occurs when "unexcited".

ya it really is 2 concepts in one.

 

[Swagster]

Which of the following species is MOST likely to exhibit color?

A. ZnCl2
B. TiO2
C. CrCl3
D. BF3

I was wondering if someone could please explain this concept and how a species could exhibit color. Thanks.

Transition metal cations with unpaired electrons can have color (like iron in blood). Cr is in the midle, so it has unpaired electrons for sure. You have to work through Zn and Ti to eliminate them.

Is this question from AAMC?

 

[TheRealAngeleno]

Thanks a lot guys!

Transition metal cations with unpaired electrons can have color (like iron in blood). Cr is in the midle, so it has unpaired electrons for sure. You have to work through Zn and Ti to eliminate them.

Is this question from AAMC?

This question is actually from a TBR In-Class packet.

 

[Rabolisk]

Simple. Ti+4 has no electrons in its valence shell, while Zn+2 has a fully filled d orbital. Zn+2 is the only transition metal with partially filled d shell. This is the best explanation without getting into crystal field theory and all that nice stuff.