Problem 131 - Chemistry and Chemical Reactivity

Question

Write the formula for each of the following compounds and indicate which ones are best described as ionic: (a) sodium hypochlorite (b) boron triiodide (c) aluminum perchlorate (d) calcium acetate (e) potassium permanganate (f) ammonium sulfite (g) potassium dihydrogen phosphate (h) disulfur dichloride (i) chlorine trifluoride (j) phosphorus trifluoride

Step-by-Step Solution

Answer

(a), (c), (d), (e), (f), and (g) are ionic. Formulas are NaClO, Al(ClO₄)₃, Ca(CH₃COO)₂, KMnO₄, (NH₄)₂SO₃, KH₂PO₄.

Step 1: Understanding Ionic and Covalent Bonds

Compounds are categorized as ionic or covalent based on the types of elements involved and how they bond. Ionic compounds typically consist of metals bonded with nonmetals and involve the transfer of electrons. Covalent compounds usually consist of nonmetals sharing electrons.

Step 2: Writing Ionic Compound Formulas

For ionic compounds, identify the cation (positively charged ion) and the anion (negatively charged ion), then balance their charges to formulate the compound. - (a) Sodium hypochlorite: Sodium (Na⁺) and hypochlorite (ClO⁻) Formula: NaClO - (c) Aluminum perchlorate: Aluminum (Al³⁺) and perchlorate (ClO₄⁻) Formula: Al(ClO₄)₃ - (d) Calcium acetate: Calcium (Ca²⁺) and acetate (CH₃COO⁻) Formula: Ca(CH₃COO)₂ - (e) Potassium permanganate: Potassium (K⁺) and permanganate (MnO₄⁻) Formula: KMnO₄ - (f) Ammonium sulfite: Ammonium (NH₄⁺) and sulfite (SO₃²⁻) Formula: (NH₄)₂SO₃ - (g) Potassium dihydrogen phosphate: Potassium (K⁺) and dihydrogen phosphate (H₂PO₄⁻) Formula: KH₂PO₄

Step 3: Writing Covalent Compound Formulas

For covalent compounds, use the prefix to determine the number of each type of atom in the molecule. - (b) Boron triiodide: Boron (B) and triiodide (I₃) Formula: BI₃ - (h) Disulfur dichloride: Disulfur (S₂) and dichloride (Cl₂) Formula: S₂Cl₂ - (i) Chlorine trifluoride: Chlorine (Cl) and trifluoride (F₃) Formula: ClF₃ - (j) Phosphorus trifluoride: Phosphorus (P) and trifluoride (F₃) Formula: PF₃

Step 4: Identifying Ionic Compounds

Review the list of compounds. Ionic compounds typically have a metal or ammonium ion: - Sodium hypochlorite (NaClO), Aluminum perchlorate (Al(ClO₄)₃), Calcium acetate (Ca(CH₃COO)₂), Potassium permanganate (KMnO₄), Ammonium sulfite ((NH₄)₂SO₃), Potassium dihydrogen phosphate (KH₂PO₄) are best described as ionic.

Key Concepts

Chemical Formulas

Chemical formulas are symbolic representations of chemical compounds. They use element symbols and numerical subscripts to convey the exact composition of a molecule. Understanding chemical formulas is crucial because they tell us not just the elements present, but also the ratio of atoms in a compound.
For example, the chemical formula for water, H₂O, indicates there are two hydrogen atoms and one oxygen atom in each molecule of water.
It’s important to understand that while ionic and covalent compounds have different structures, their chemical formulas still serve the same fundamental purpose of denoting the composition of compounds.

• **Ionic compounds** often consist of a metal and a nonmetal, leading to the transfer of electrons from the metal to the nonmetal.
• **Covalent compounds** usually consist of two or more nonmetals sharing electrons.

By using chemical formulas, we can quickly convey complex chemical information in a simple, standardized format.

Covalent Compounds

Covalent compounds are characterized by the sharing of electrons between atoms, usually nonmetals. These atoms join together to form molecules by sharing electrons, thereby achieving a stable electron configuration.
Unlike ionic compounds, which form lattice structures, covalent compounds form distinct molecules.
The prefix system is often employed in naming and writing the chemical formulas for covalent compounds, using prefixes such as mono-, di-, tri-, tetra-, etc. For instance, **boron triiodide** (BI₃) consists of one boron atom covalently bonded to three iodine atoms.
Similarly, **disulfur dichloride** (S₂Cl₂) has two sulfur atoms covalently bonded to two chlorine atoms. This naming convention allows us to understand the composition of the molecules at a glance.

This specific nomenclature helps understand the form and structure of the compound.

Knowing about covalent compounds is key in many areas of chemistry, especially organic chemistry, where complex molecules are built through covalent bonding.

Ionic Bonds

Ionic bonds form when a metal transfers one or more electrons to a nonmetal, resulting in the formation of charged ions: positive ions (cations) and negative ions (anions).
These opposite charges attract each other, creating a strong bond and forming ionic compounds with a crystalline lattice structure.
**Sodium hypochlorite** (NaClO) exemplifies this, as sodium (Na⁺) donates an electron to hypochlorite (ClO⁻), resulting in an ionic compound.
Others include **calcium acetate** (Ca(CH₃COO)₂) and **potassium permanganate** (KMnO₄), where calcium and potassium ions form ionic bonds with acetate and permanganate ions, respectively.

Ionic bonds are generally strong due to the electrostatic forces between the ions.

These compounds often have high melting and boiling points.

Grasping ionic bonds is essential to understanding how various compounds are formed and their properties in different chemical reactions.

Charge Balancing

Charge balancing is crucial in forming ionic compounds to ensure that the overall charge of the compound is zero.
In an ionic compound, the total positive charge contributed by the cations must equal the total negative charge contributed by the anions.
This balance ensures that the compound is electrically neutral. To create the formula for **aluminum perchlorate** (Al(ClO₄)₃), for instance, the charges need to balance. Aluminum has a charge of 3+ (Al³⁺) and each perchlorate ion has a charge of 1- (ClO₄⁻). Using three perchlorate ions balances the positive charge from the aluminum.

Charge balancing is achieved by adjusting the number of ions needed to cancel each other's charges out.

This fundamental concept is crucial for students to grasp, as it forms the basis of predicting and constructing the chemical formulas of ionic compounds.