Question

Give the chemical formula for each of the following ionic compounds: (a) sodium phosphate, (b) zinc nitrate, (c) barium bromate, (d) iron(II) perchlorate, (e) cobalt(II) hydrogen carbonate, (f) chromium(III) acetate, (g) potassium dichromate.

Short answer

The chemical formulas for the given ionic compounds are: (a) \(Na_3PO_4\), (b) \(Zn(NO_3)_2\), (c) \(Ba(BrO_3)_2\), (d) \(Fe(ClO_4)_2\), (e) \(Co(HCO_3)_2\), (f) \(Cr(CH_3COO)_3\), and (g) \(K_2Cr_2O_7\).

Step-by-step solution

(a) Sodium phosphate

Sodium ions have a charge of +1 (\(Na^+\)), and phosphate ions have a charge of -3 (\(PO_4^{3-}\)). To balance the charges, we need three sodium ions to match one phosphate ion, which results in the chemical formula: \(Na_3PO_4\).

(b) Zinc nitrate

Zinc ions have a charge of +2 (\(Zn^{2+}\)), and nitrate ions have a charge of -1 (\(NO_3^{-}\)). Therefore, we need two nitrate ions to match one zinc ion, giving us the chemical formula: \(Zn(NO_3)_2\).

(c) Barium bromate

Barium ions have a charge of +2 (\(Ba^{2+}\)), and bromate ions have a charge of -1 (\(BrO_3^{-}\)). We need two bromate ions to balance one barium ion. This gives us the chemical formula: \(Ba(BrO_3)_2\).

(d) Iron(II) perchlorate

Iron(II) ions have a charge of +2 (\(Fe^{2+}\)), and perchlorate ions have a charge of -1 (\(ClO_4^{-}\)). To balance the charges, we need two perchlorate ions to match one iron(II) ion, resulting in the chemical formula: \(Fe(ClO_4)_2\).

(e) Cobalt(II) hydrogen carbonate

Cobalt(II) ions have a charge of +2 (\(Co^{2+}\)), and hydrogen carbonate ions have a charge of -1 (\(HCO_3^{-}\)). To balance the charges, we need two hydrogen carbonate ions to match one cobalt(II) ion, giving us the chemical formula: \(Co(HCO_3)_2\).

(f) Chromium(III) acetate

Chromium(III) ions have a charge of +3 (\(Cr^{3+}\)), and acetate ions have a charge of -1 (\(CH_3COO^{-}\)). To balance the charges, we need three acetate ions to match one chromium(III) ion, which results in the chemical formula: \(Cr(CH_3COO)_3\).

(g) Potassium dichromate

Potassium ions have a charge of +1 (\(K^+\)), and dichromate ions have a charge of -2 (\(Cr_2O_7^{2-}\)). We need two potassium ions to balance one dichromate ion. This gives the chemical formula: \(K_2Cr_2O_7\).

Key concepts

Chemical Formulas

Chemical formulas are the backbone of chemistry, providing a simple way to convey complex information about compounds. They represent the elements that make up a compound and show their proportions. A chemical formula is composed of element symbols and subscripts which indicate the number of each type of atom present in the molecule.
For ionic compounds, these formulas are derived from the charges of the ions that compose them. In the context of ionic compounds, the combination of cations (positive ions) and anions (negative ions) must result in a neutral compound. This means that the total positive charge must equal the total negative charge. For example, in sodium phosphate ( N N a_3PO_4 ena), there are three sodium ions each with a +1 charge balancing one phosphate ion with a -3 charge. This results in a neutral overall charge.

Charge Balance

Charge balance is a crucial concept in forming stable ionic compounds. An ionic compound must have a net charge of zero, meaning the positive and negative charges cancel each other out. This is achieved by combining the cations and anions in the right proportions.

• Start by identifying the charge of the ions involved. For example, a zinc ion has a +2 charge and a nitrate ion has a -1 charge.
• Next, determine the ratio of ions needed. In zinc nitrate ( Zn(NO_3)_2 zn), two nitrate ions are needed to balance the +2 charge of a single zinc ion.
• The placement of parentheses in the chemical formula indicates the need for multiple polyatomic ions, like the two nitrate groups in zinc nitrate.

By balancing the positive and negative charges, we achieve a stable, neutral ionic compound.

Polyatomic Ions

Polyatomic ions are ions that contain more than one atom. These ions often act as a single unit within a compound, and they have a specific net charge that contributes to the charge balance in ionic compounds. Recognizing and using polyatomic ions correctly is vital for writing accurate chemical formulas.

• Some common polyatomic ions include phosphate ( PO_4^{3-} po), nitrate ( NO_3^{-} no), and dichromate ( Cr_2O_7^{2-} cr).
• Each polyatomic ion has a specific charge that does not change, no matter how many ions you have.
• In molecular formulas, polyatomic ions are often represented with parentheses if there is more than one of these ions within a compound. For example, the presence of two bromate ions in barium bromate is shown as ( Ba(BrO_3)_2 ba) to reflect the need for two bromate ions per one barium ion.

The charge of polyatomic ions plays a significant role in determining how they combine with other ions to form stable ionic compounds.