Ionic Compounds with Polyatomic Ions

Ionic Compounds with Polyatomic Ions 1. Physical properties Compound K2CO3; Appearance: White, solid, crystalline Density: 2.29 g/cm³ Melting Point: 891°C Formulas of ionic compounds: Name: Potassium carbonate Positive Ion: K1+ Negative Ion: CO3 Formula: K2CO3 Name: Sodium nitrate Positive Ion: Na1+ Negative Ion: NO3 Formula: NaNO3 Name: Calcium bicarbonate Positive Ion: Ca2+ Negative Ion: HCO3 Formula: Ca(HCO3)2 Name: Chromium (III) hydroxide Positive Ion: Cr3+ Negative Ion: OH1- Formula: Cr(OH)3 Name: Lithium phosphate Positive Ion: Li1+ Negative Ion: PO4 Formula: Li3PO4 Name: Potassium sulfate Positive Ion: K1+ Negative Ion: SO4 Formula: K2SO4 Names of ionic compounds: Formula: CaSO4 Positive Ion: Ca2+ Negative Ion: SO4 Name: Calcium sulfate Formula: Al(NO3)3 Positive Ion: Al3+ Negative Ion: NO3 Name: Aluminum nitrate Formula: Na2CO3 Positive Ion: Na1+ Negative Ion: CO3 Name: Sodium carbonate Formula: MgSO3 Positive Ion: Mg2+ Negative Ion: SO3 Name: Magnesium sulfite Formula: Cu(OH)2 Positive Ion: Cu2+ Negative Ion: OH1- Name: Copper(II) hydroxide Formula: Mg3(PO4)2 Positive Ion: Mg2+ Negative Ion: PO4 Name: Magnesium phosphate Molecular Compounds 1. Physical properties Compound: Water; H2O Appearance: Colorless; liquid Density: 1.0 g/mL Melting Point: 0°C Formulas of molecular compounds: Name: Dinitrogen pentoxide Formula: N2O5 Name: Silicon tetrachloride Formula: SiCl4 Name: Dinitrogen trisulfide Formula: N2S3 Name: Oxygen difluoride Formula: OF2 Name: Iodine heptafluoride Formula: IF7 Name: Phosphorus tribromide Formula: PBr3

The Correct Answer and Explanation is:

Correct Answers Summary

Ionic Compounds with Polyatomic Ions:

1. Potassium carbonate
   • Positive Ion: K⁺
   • Negative Ion: CO₃²⁻
   • Formula: K₂CO₃
   • Appearance: White, solid, crystalline
   • Density: 2.29 g/cm³
   • Melting Point: 891°C
2. Sodium nitrate
   • Positive Ion: Na⁺
   • Negative Ion: NO₃⁻
   • Formula: NaNO₃
3. Calcium bicarbonate
   • Positive Ion: Ca²⁺
   • Negative Ion: HCO₃⁻
   • Formula: Ca(HCO₃)₂
4. Chromium(III) hydroxide
   • Positive Ion: Cr³⁺
   • Negative Ion: OH⁻
   • Formula: Cr(OH)₃
5. Lithium phosphate
   • Positive Ion: Li⁺
   • Negative Ion: PO₄³⁻
   • Formula: Li₃PO₄
6. Potassium sulfate
   • Positive Ion: K⁺
   • Negative Ion: SO₄²⁻
   • Formula: K₂SO₄

Additional Names from Formulas:

1. CaSO₄
   • Positive Ion: Ca²⁺
   • Negative Ion: SO₄²⁻
   • Name: Calcium sulfate
2. Al(NO₃)₃
   • Positive Ion: Al³⁺
   • Negative Ion: NO₃⁻
   • Name: Aluminum nitrate
3. Na₂CO₃
   • Positive Ion: Na⁺
   • Negative Ion: CO₃²⁻
   • Name: Sodium carbonate
4. MgSO₃
   • Positive Ion: Mg²⁺
   • Negative Ion: SO₃²⁻
   • Name: Magnesium sulfite
5. Cu(OH)₂
   • Positive Ion: Cu²⁺
   • Negative Ion: OH⁻
   • Name: Copper(II) hydroxide
6. Mg₃(PO₄)₂
   • Positive Ion: Mg²⁺
   • Negative Ion: PO₄³⁻
   • Name: Magnesium phosphate

Molecular Compounds:

1. Water – H₂O
   • Appearance: Colorless liquid
   • Density: 1.0 g/mL
   • Melting Point: 0°C

Formulas of Molecular Compounds:

1. Dinitrogen pentoxide – N₂O₅
2. Silicon tetrachloride – SiCl₄
3. Dinitrogen trisulfide – N₂S₃
4. Oxygen difluoride – OF₂
5. Iodine heptafluoride – IF₇
6. Phosphorus tribromide – PBr₃

Explanation

Ionic and molecular compounds differ significantly in their bonding and physical properties. Ionic compounds consist of metals bonded to nonmetals or polyatomic ions. These compounds form crystalline solids due to the strong electrostatic attraction between oppositely charged ions. For example, potassium carbonate (K₂CO₃) is composed of potassium ions (K⁺) and carbonate ions (CO₃²⁻), forming a stable, solid lattice with high melting points and considerable density. Many ionic compounds, such as calcium sulfate (CaSO₄) and sodium nitrate (NaNO₃), dissolve in water and conduct electricity in solution due to the presence of free ions.

Polyatomic ions like NO₃⁻ (nitrate), SO₄²⁻ (sulfate), and PO₄³⁻ (phosphate) are groups of covalently bonded atoms that carry a net charge. These ions act as a single unit when forming ionic compounds. The correct formula must balance the total positive and negative charges. For instance, in lithium phosphate (Li₃PO₄), three lithium ions (Li⁺) are needed to balance one phosphate ion (PO₄³⁻).

On the other hand, molecular compounds are formed from nonmetals that share electrons through covalent bonds. They typically have lower melting points and do not conduct electricity in solution. Water (H₂O) is a common molecular compound, known for its liquid state at room temperature and its vital role in life. Other examples include phosphorus tribromide (PBr₃) and dinitrogen pentoxide (N₂O₅). These compounds are often named using prefixes to indicate the number of each atom.

Understanding the distinction between ionic and molecular compounds is key to predicting their behavior, reactivity, and applications in various scientific and industrial contexts.