Question

Write the formula for each of the following chromium-containing ions, including the overall charge of the ion. a. chromous b. chromate c. chromic d. dichromate

Short answer

a. Chromous Ion: \(Cr^{2+}\) with a +2 charge. b. Chromate Ion: \(CrO_4^{2-}\) with a -2 charge. c. Chromic Ion: \(Cr^{3+}\) with a +3 charge. d. Dichromate Ion: \(Cr_2O_7^{2-}\) with a -2 charge.

Step-by-step solution

a. Chromous Ion

Chromous refers to chromium in its +2 oxidation state. The chromous ion is represented as \(Cr^{2+}\). The overall charge of the ion is +2.

b. Chromate Ion

Chromate refers to the polyatomic ion with chromium in its +6 oxidation state and the formula \(CrO_4^{2-}\). The overall charge of the ion is -2.

c. Chromic Ion

Chromic refers to chromium in its +3 oxidation state. The chromic ion is represented as \(Cr^{3+}\). The overall charge of the ion is +3.

d. Dichromate Ion

Dichromate refers to the polyatomic ion consisting of two chromium atoms in their +6 oxidation state with the formula \(Cr_2O_7^{2-}\). The overall charge of the ion is -2.

Key concepts

Oxidation States

Oxidation states, also known as oxidation numbers, indicate how many electrons an atom has gained or lost in forming a compound. They help describe the electron distribution in ions and molecules. For chromium ions, these states will change depending on their chemical environments and compounds they are part of.

1. **Chromous Ion**: Chromium has an oxidation state of +2 in the chromous ion, represented as \(Cr^{2+}\). This means each chromium atom has lost two electrons.2. **Chromic Ion**: The chromic ion exhibits chromium in a +3 oxidation state or \(Cr^{3+}\), signifying three electrons are lost by each chromium atom.3. **Chromate and Dichromate Ions**: Both chromate, \(CrO_4^{2-}\), and dichromate, \(Cr_2O_7^{2-}\), have chromium in the +6 oxidation state, indicating each chromium atom has lost six electrons.

Understanding oxidation states is fundamental in predicting how substances will react chemically. Different oxidation states can lead to very different properties and reactivities in ions.

Ion Charges

Ion charge refers to the electric charge that an ion carries. This charge results from the loss or gain of electrons. Identifying ion charges is crucial for understanding chemical reactivity and stability.

- **Chromous Ion**: The chromous ion \(Cr^{2+}\) possesses a charge of +2.
- **Chromic Ion**: The chromic ion \(Cr^{3+}\) has a charge of +3. Electrons are further removed compared to chromous, making chromic heavier in charge.- **Chromate Ion**: \(CrO_4^{2-}\) carries a -2 charge. It forms due to the bonding between chromium and oxygen where additional electrons are shared.- **Dichromate Ion**: While composed of two chromiums, \(Cr_2O_7^{2-}\) also maintains an overall charge of -2 due to its extra shared electrons from oxygen bonds.
Knowing ion charges allows one to predict how ions interact, combine, or separate in chemical reactions. It affects ion solubility, crystal structure, and conductivity.

Chemical Formulas

Chemical formulas are symbolic representations conveying the composition of molecules and ions. They disclose which elements are present and in what proportions.

- **Chromous Ion**: This is simply denoted as \(Cr^{2+}\), indicating one chromium atom with a +2 charge.- **Chromic Ion**: Represented as \(Cr^{3+}\), it shows one chromium atom with a +3 charge.- **Chromate Ion**: \(CrO_4^{2-}\) tells us that one chromium atom is bonded with four oxygen atoms and the entire ion has a -2 charge.- **Dichromate Ion**: The formula \(Cr_2O_7^{2-}\) identifies two chromium atoms connected with seven oxygen atoms, sharing a -2 charge.
Understanding chemical formulas is essential in cogently conveying complex chemical relationships and reactions. It allows chemists to communicate and predict chemical structures and observable properties.