chromium

Question 1

What are the typical properties of a transitional metal?

Answer 1

• Partly filled d orbitals
• Coloured compounds (due to d-d transitions)
• Complex formation
• Variable oxidation states
• Catalysis

These properties are characteristic of transition metals, including chromium.

Question 2

What is the atomic configuration of Chromium?

Answer 2

[Ar] 3d5 4s1

This configuration indicates the distribution of electrons in Chromium.

Question 3

What is the most stable and common oxidation state of Chromium?

Answer 3

Cr(III)

This oxidation state is characterized by thousands of compounds.

Question 4

What are the oxidation states of Chromium that can be found?

Answer 4

• Cr(VI)
• Cr(0)
• Cr(-I)

Chromium exhibits a wide range of oxidation states, but Cr(III) is the most stable.

Question 5

What are the main compounds of Cr(VI)?

Answer 5

• Chromates (CrO4^2-)
• Dichromates (Cr2O7^2-)

These compounds are powerful oxidizing agents formed by the oxidation of Cr(III).

Question 6

What happens when hydrogen peroxide is added to an acidified solution of a chromate?

Answer 6

A deep violet-blue peroxo compound CrO(O2)2 is formed.

This compound can decompose in aqueous solution but is more stable in an ether solution.

Question 7

What is the characteristic of Cr(III) in terms of complex formation?

Answer 7

Forms stable salts with all common anions and complexes with virtually any species capable of donating an electron pair.

These complexes may be cationic, anionic, or neutral and are mostly octahedral.

Question 8

What is the structure of the CrO(O2)2py adduct?

Answer 8

Pentagonal pyramidal

This structure can be isolated from the ether solution of CrO(O2)2.

Question 9

What is the magnetic moment of Cr(III)?

Answer 9

µs = 3.87 BM

This is based on the d3 configuration, which has three unpaired electrons.

Question 10

What type of ligands do Cr(II) complexes typically form?

Answer 10

• N-donor bidentate ligands
• Octahedral complexes
• Tetrahedral complexes

Cr(II) complexes are sensitive to oxidation when wet.

Question 11

What is the significance of the Cr-Cr bond distance in Cr(II) complexes?

Answer 11

Short bond distance of 235 pm indicates strong interaction between the two Cr atoms.

This suggests all d orbital electrons are involved in the bonding.

Question 12

What type of bond is formed by the overlap of dz2 orbitals in Cr(II) complexes?

Answer 12

σ bond

This bond formation contributes to the complex’s stability.

Question 13

What is the role of dxy orbitals in Cr(II) bonding?

Answer 13

Forms δ (delta) bonds

This contributes to the quadruple bond formation in Cr=Cr complexes.

Question 14

What is the oxidation tendency of Cr(II)?

Answer 14

Strongly reducing in aqueous solution

It tends to be oxidized to Cr(III).

Question 15

What is the typical coordination geometry for Cr(III) complexes?

Answer 15

Octahedral

This geometry is common for Cr(III) complexes due to its d3 configuration.

Question 16

Fill in the blank: The most important Cr(VI) compounds are the _______ and _______.

Answer 16

chromates, dichromates

These compounds are formed in aqueous solution by the oxidation of Cr(III).

Question 17

True or False: Cr(IV) and Cr(V) are stable oxidation states of chromium.

Answer 17

False

Cr(IV) and Cr(V) are relatively rare and readily undergo disproportionation.