Chromium, a versatile transition metal, primarily exhibits a valency of 2, but also commonly displays valencies of 3 and 6 in its various compounds.
Understanding Valency
Valency refers to the combining capacity of an element, indicating the number of electrons an atom can gain, lose, or share to form chemical bonds with other atoms. For many elements, valency is a fixed number. However, transition metals like chromium often display multiple valencies (also known as oxidation states) due to the involvement of both s and d orbital electrons in bonding.
Common Valencies of Chromium
While chromium is known for its diverse chemical behavior, its most frequently observed valencies are:
- Valency 2 (Divalent): This valency is observed in compounds where chromium loses two electrons. An example is chromium(II) chloride (CrCl₂). Atomic data highlights this as a significant valency for Chromium (Atomic Number 24).
- Valency 3 (Trivalent): This is often the most stable and common valency for chromium. It is seen in many chromium compounds, such as chromium(III) oxide (Cr₂O₃) and chromium(III) chloride (CrCl₃).
- Valency 6 (Hexavalent): This higher valency is found in strong oxidizing agents like chromates (e.g., potassium chromate, K₂CrO₄) and dichromates (e.g., potassium dichromate, K₂Cr₂O₇). Compounds with chromium in a +6 oxidation state are often vividly colored and can be toxic.
Why Multiple Valencies?
The ability of chromium to exhibit multiple valencies is characteristic of transition metals. This phenomenon arises from the close energy levels of their ns and (n-1)d orbitals. In chromium, for instance, electrons from both the 4s and 3d orbitals can participate in bonding, leading to various stable oxidation states depending on the chemical environment and the nature of the bonding partners. This flexibility allows chromium to form a wide range of compounds with diverse properties and applications.
Summary Table of Chromium Valencies
| Valency | Common Compounds (Examples) | Description |
|---|---|---|
| 2 | CrCl₂ (Chromium(II) chloride) | Divalent, often readily oxidized. |
| 3 | Cr₂O₃ (Chromium(III) oxide) | Trivalent, very stable and most common. |
| 6 | K₂CrO₄ (Potassium chromate) | Hexavalent, strong oxidizing agent, often toxic. |
For further details on valency and oxidation states, you can explore resources like Wikipedia's article on Valency or LibreTexts Chemistry.
