Problem 87 - Chemistry and Chemical Reactivity

Question

Write the formula for each of the following compounds, and tell 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

Ionic compounds: NaClO, Al(ClO₄)₃, Ca(C₂H₃O₂)₂, KMnO₄, (NH₄)₂SO₃, KH₂PO₄. Others are covalent.

Step 1: Identify Ionic Compounds

Ionic compounds are typically formed between metals and non-metals, where electrons are transferred from one atom to another. Let's identify which of the compounds listed consist of both metal and non-metal components: - Sodium hypochlorite (sodium is a metal, hypochlorite is a polyatomic anion) - Aluminum perchlorate (aluminum is a metal, perchlorate is a polyatomic anion) - Calcium acetate (calcium is a metal, acetate is a polyatomic anion) - Potassium permanganate (potassium is a metal, permanganate is a polyatomic anion) - Ammonium sulfite (ammonium acts like a metal, sulfite is a polyatomic anion) - Potassium dihydrogen phosphate (potassium is a metal, dihydrogen phosphate is a polyatomic anion) These are best described as ionic.

Step 2: Write the Formula for Each Compound

Now, let's assign the chemical formulas for each compound: (a) Sodium hypochlorite: NaClO (b) Boron triiodide: BI₃ (c) Aluminum perchlorate: Al(ClO₄)₃ (d) Calcium acetate: Ca(C₂H₃O₂)₂ (e) Potassium permanganate: KMnO₄ (f) Ammonium sulfite: (NH₄)₂SO₃ (g) Potassium dihydrogen phosphate: KH₂PO₄ (h) Disulfur dichloride: S₂Cl₂ (i) Chlorine trifluoride: ClF₃ (j) Phosphorus trifluoride: PF₃

Step 3: Determine Ionic vs. Covalent

Based on the identification of ionic compounds earlier, the following compounds are ionic: (a) Sodium hypochlorite (NaClO) (c) Aluminum perchlorate (Al(ClO₄)₃) (d) Calcium acetate (Ca(C₂H₃O₂)₂) (e) Potassium permanganate (KMnO₄) (f) Ammonium sulfite ((NH₄)₂SO₃) (g) Potassium dihydrogen phosphate (KH₂PO₄) Boron triiodide (BI₃), disulfur dichloride (S₂Cl₂), chlorine trifluoride (ClF₃), and phosphorus trifluoride (PF₃) are molecular (covalent) compounds because they are composed entirely of nonmetals.

Key Concepts

Chemical Formulas

Chemical formulas are essential expressions that represent substances using their elemental symbols. Each element in a formula has a subscript number indicating the number of atoms of that element in a single molecule of the compound.
For example, the formula for water is \( H_2O \), indicating that each molecule contains two hydrogen atoms and one oxygen atom.
In chemical formulas, uppercase letters denote different elements, while lowercase numbers provide quantities. Symbols without subscripts mean there is only one atom of that element present.
Understanding chemical formulas helps in visualizing the composition of chemical compounds, whether ionic or covalent.

Ionic Compounds Identification

Ionic compounds form through the transfer of electrons from one atom to another, resulting in charged particles called ions. These ions include positively charged cations and negatively charged anions. Typically, metals form cations and non-metals form anions. Ionic compounds typically consist of a combination of these two types of ions.
To identify an ionic compound, look for elements from opposite sides of the periodic table—usually metals and non-metals. Examples include sodium hypochlorite \((NaClO)\) and calcium acetate \((Ca(C_2H_3O_2)_2)\).
Additionally, recognizing the presence of polyatomic ions can also signal an ionic compound. These compounds often have high melting points and are solid at room temperature.

Covalent Compounds Identification

Covalent compounds are formed when two or more non-metal atoms share electrons, thereby creating a stable bond. Unlike ionic compounds, no charged particles are involved. Covalent bonds result in molecular compounds, which can exist in solid, liquid, or gaseous forms at room temperature.
These compounds typically involve atoms from the same side of the periodic table. Boron triiodide \((BI_3)\), chlorine trifluoride \((ClF_3)\), and phosphorus trifluoride \((PF_3)\) are a few examples.
Covalent compounds usually have lower melting and boiling points compared to ionic compounds. Recognizing these characteristics helps in distinguishing covalent bonds from ionic ones.

Polyatomic Ions

Polyatomic ions are charged entities consisting of two or more atoms covalently bonded, carrying an overall charge. These ions can form ionic compounds by interacting with oppositely charged ions.
Examples of common polyatomic ions include acetate \((C_2H_3O_2^-)\), perchlorate \((ClO_4^-)\), sulfite \((SO_3^{2-})\), and phosphate \((PO_4^{3-})\). Indeed, compounds like ammonium sulfite \(((NH_4)_2SO_3)\) incorporate such ions.
Recognizing polyatomic ions is crucial for writing correct chemical formulas. They often maintain their structural integrity in reactions and influence compound solubility and chemical behavior.