Question

Write the chemical formulas for the following compounds: (a) aluminum hydroxide, (b) potassium sulfate, (c) copper(I) oxide, ( \(\mathbf{d} )\) zinc nitrate, (e) mercury(II) bromide, (f) iron(III) carbonate, (g) sodium hypobromite.

Short answer

The chemical formulas for the compounds are: (a) Al(OH)\(_3\) (b) K\(_2\)SO\(_4\) (c) Cu\(_2\)O (d) Zn(NO\(_3\))\(_2\) (e) HgBr\(_2\) (f) Fe\(_2\)(CO\(_3\))\(_3\) (g) NaBrO

Step-by-step solution

(a) Aluminum hydroxide

1. Aluminum (Al) has a charge of +3 and hydroxide (OH) has a charge of -1. 2. To form a neutral compound, we need 1 Al and 3 OH ions. 3. The chemical formula for aluminum hydroxide is Al(OH)\(_3\).

(b) Potassium sulfate

1. Potassium (K) has a charge of +1 and sulfate (SO\(_4\)) has a charge of -2. 2. To form a neutral compound, we need 2 K and 1 SO\(_4\) ions. 3. The chemical formula for potassium sulfate is K\(_2\)SO\(_4\).

(c) Copper(I) oxide

1. Copper(I) (Cu) has a charge of +1 and oxide (O) has a charge of -2. 2. To form a neutral compound, we need 2 Cu and 1 O ions. 3. The chemical formula for copper(I) oxide is Cu\(_2\)O.

(d) Zinc nitrate

1. Zinc (Zn) has a charge of +2 and nitrate (NO\(_3\)) has a charge of -1. 2. To form a neutral compound, we need 1 Zn and 2 NO\(_3\) ions. 3. The chemical formula for zinc nitrate is Zn(NO\(_3\))\(_2\).

(e) Mercury(II) bromide

1. Mercury(II) (Hg) has a charge of +2 and bromide (Br) has a charge of -1. 2. To form a neutral compound, we need 1 Hg and 2 Br ions. 3. The chemical formula for mercury(II) bromide is HgBr\(_2\).

(f) Iron(III) carbonate

1. Iron(III) (Fe) has a charge of +3 and carbonate (CO\(_3\)) has a charge of -2. 2. To form a neutral compound, we need 2 Fe and 3 CO\(_3\) ions. 3. The chemical formula for iron(III) carbonate is Fe\(_2\)(CO\(_3\))\(_3\).

(g) Sodium hypobromite

1. Sodium (Na) has a charge of +1 and hypobromite (BrO) has a charge of -1. 2. To form a neutral compound, we need 1 Na and 1 BrO ion. 3. The chemical formula for sodium hypobromite is NaBrO.

Key concepts

Writing Chemical Formulas

Understanding how to write chemical formulas is vital for students studying chemistry. It's the way we represent the identity of substances and their proportions in a compound. Each element has a symbol, such as Al for aluminum, and each type of ion carries a charge which guides us in combining them.

For instance, if we want to write the formula for aluminum hydroxide, we need to consider the charges. Aluminum has a +3 charge and hydroxide has a -1 charge. To balance these charges so they add up to zero, we need three hydroxide ions for every aluminum ion. This gives us Al(OH)₃ as the neutral compound. The parentheses are essential when indicating more than one of a polyatomic ion—as in this case, with hydroxide.

In the case of copper(I) oxide, copper with a +1 charge requires two copper ions to balance the -2 charge of a single oxide ion, leading to the formula Cu₂O. Remember that the number of atoms or polyatomic ions is indicated by the subscript following the element or group, without any charges shown in the final formula.

Ionic Compound Composition

Ionic compounds are made up of positively charged cations and negatively charged anions that combine in ratios which neutralize their charges. For an ionic compound to be stable, the total positive charge must balance out the total negative charge, leading to a net charge of zero.

Take the example of zinc nitrate: zinc has a +2 charge, and nitrate has a -1 charge. To achieve neutrality, we pair one zinc ion with two nitrate ions, resulting in Zn(NO₃)₂. It's this charge balancing act that dictates the ratios in which ions come together to form a compound.

When writing formulas for ionic compounds with transition metals, like iron(III) carbonate, you need to pay attention to the metal's oxidation state indicated by the Roman numeral. Here, iron(III) means each iron ion has a +3 charge; thus, you'll need two iron ions to balance three carbonate ions with a -2 charge, leading to Fe₂(CO₃)₃.

Polyatomic Ions

Polyatomic ions are clusters of atoms that carry an overall charge, making them crucial participants in the formation of many ionic compounds. Their composition can look complex, but recognizing common polyatomic ions helps you write chemical formulas correctly.

Some widely known polyatomic ions include sulfate (SO₄)^2- and nitrate (NO₃)^-. When these ions form compounds, they behave as single units. For instance, potassium sulfate requires two potassium ions to balance one sulfate ion, giving us K₂SO₄. It's the same with nitrate in zinc nitrate, where one zinc ion balances two nitrate ions, resulting in Zn(NO₃)₂.

Understanding the charge on polyatomic ions, such as carbonate (CO₃)^2-, is also key to correctly determining the ratio between the ions in compounds like iron(III) carbonate. Polyatomic ions often have common endings, such as '-ate' or '-ite', which can help indicate the presence of oxygen in their composition and aid in their identification.