Problem 66 - Chemistry: The Central Science in SI Units, Global Edition

Question

Predict whether each of the following compounds is molecular or ionic: \((\mathbf{a}) \mathrm{BI}_{3}(\mathbf{b}) \mathrm{N}\left(\mathrm{CH}_{3}\right)_{3}(\mathbf{c}) \mathrm{Zr}\left(\mathrm{NO}_{3}\right)_{2}\) (d) \(\mathrm{N}_{2} \mathrm{H}_{4}(\mathbf{e})\) \(\mathrm{OsCO}_{3}(\mathbf{f}) \mathrm{H}_{2} \mathrm{SO}_{4}(\mathbf{g}) \mathrm{HgS}(\mathbf{h}) \mathrm{IOH}\)

Step-by-Step Solution

Answer

(a) BI3: Molecular (b) N(CH3)3: Molecular (c) Zr(NO3)2: Ionic (d) N2H4: Molecular (e) OsCO3: Ionic (f) H2SO4: Molecular (g) HgS: Ionic (h) IOH: Molecular

Step 1: (a) BI3

Boron (B) and Iodine (I) are both non-metals, so the bond between them is covalent. Hence, BI3 is a molecular compound.

Step 2: (b) N(CH3)3

Nitrogen (N) and Carbon (C) are both non-metals, and bonds formed within N(CH3)3 are covalent. Therefore, N(CH3)3 is a molecular compound.

Step 3: (c) Zr(NO3)2

Zirconium (Zr) is a metal, while Nitrogen (N) and Oxygen (O) are non-metals. Thus, this compound has ionic bonds between its metal and non-metal elements. Therefore, Zr(NO3)2 is an ionic compound.

Step 4: (d) N2H4

Both Nitrogen (N) and Hydrogen (H) are non-metals. Therefore, the bonds within N2H4 are covalent, making N2H4 a molecular compound.

Step 5: (e) OsCO3

Osmium (Os) is a metal, while Carbon (C) and Oxygen (O) are non-metals. This compound has ionic bonds between its metal and non-metal elements. Hence, OsCO3 is an ionic compound.

Step 6: (f) H2SO4

Hydrogen (H), Sulfur (S), and Oxygen (O) are all non-metals. Consequently, the bonds within H2SO4 are covalent, making H2SO4 a molecular compound.

Step 7: (g) HgS

Mercury (Hg) is a metal, and Sulfur (S) is a non-metal. HgS has an ionic bond between its metal and non-metal elements, making HgS an ionic compound.

Step 8: (h) IOH

Iodine (I) and Hydrogen (H) are non-metals, and Oxygen (O) is also a non-metal. The bonds between these elements in IOH are covalent. Hence, IOH is a molecular compound.

Key Concepts

Ionic Compounds

Ionic compounds are formed when there is a transfer of electrons from one atom to another, leading to the formation of ions. This usually happens between metal and non-metal elements. The metal atom loses electrons to become a positively charged ion (cation), while the non-metal atom gains electrons to become a negatively charged ion (anion). Some key features of ionic compounds include:

• High melting and boiling points due to strong attractions between ions.
• They are usually solid at room temperature.
• They conduct electricity when dissolved in water or melted.

For example, in the compound Zr(NO₃)₂, zirconium (Zr) is a metal, and nitrogen (N) along with oxygen (O) are non-metals. This combination forms an ionic compound because zirconium donates electrons to the non-metals.

Molecular Compounds

Molecular compounds, also known as covalent compounds, form when two or more non-metal elements share electrons. This electron sharing results in molecules, which are distinct units that retain the compound's properties. Some characteristics of molecular compounds include:

• Lower melting and boiling points compared to ionic compounds.
• They are often found as gases or liquids at room temperature, although some are solids.
• Molecular compounds do not conduct electricity in any state.

BI₃ is a fine example of a molecular compound. It consists of boron and iodine, both of which are non-metal elements, making it a molecular compound due to shared electrons.

Covalent Bonds

Covalent bonds occur in molecular compounds, where atoms share pairs of electrons. These bonds mold the structure and properties of the resulting molecules. Key attributes include:

• Strength, as covalent bonds hold molecules together tightly.
• Directionality, meaning the bonds have specific geometries in space.

In N(CH₃)₃, covalent bonds form between nitrogen and carbon. Nitrogen and hydrogen in N₂H₄ also create covalent bonds, showcasing how non-metallic atoms can bond covalently to create diverse molecules with varying properties.

Metal and Non-Metal Elements

Understanding the difference between metal and non-metal elements is essential for predicting whether a compound is ionic or molecular.

• Metals are typically shiny, malleable, and good conductors of electricity and heat. They tend to lose electrons during reactions, forming cations.
• Non-metals have a variety of properties. They are usually not shiny, often brittle, and poor conductors. In reactions, they gain electrons, forming anions.

When metals combine with non-metals, they form ionic compounds, such as HgS (mercury sulfide), where mercury (metal) and sulfur (non-metal) interact. Conversely, a combination of non-metals, such as iodate in IOH, results in a molecular structure due to the sharing of electrons.