Problem 65 - Chemistry: The Central Science in SI Units, Global Edition

Question

Predict whether each of the following compounds is molecular or ionic: \((\mathbf{a}) \mathrm{HClO}_{4}(\mathbf{b}) \mathrm{CH}_{3} \mathrm{OCH}_{3}(\mathbf{c}) \mathrm{Mg}\left(\mathrm{NO}_{3}\right)_{2}(\mathbf{d}) \mathrm{H}_{2} \mathrm{~S}\) (e) \(\mathrm{TiCl}_{4}(\mathbf{f}) \mathrm{K}_{2} \mathrm{O}_{2}(\mathbf{g}) \mathrm{PCl}_{5}(\mathbf{h}) \mathrm{P}(\mathrm{OH})_{3} .\)

Step-by-Step Solution

Answer

\( \begin{array}{ | l | l | } \hline \textbf{Compound} & \textbf{Classification} \\ \hline \mathrm{HClO}_{4} & \text{Molecular} \\ \hline \mathrm{CH}_{3}\mathrm{OCH}_{3} & \text{Molecular} \\ \hline \mathrm{Mg}\left(\mathrm{NO}_{3}\right)_{2} & \text{Ionic} \\ \hline \mathrm{H}_{2}\mathrm{S} & \text{Molecular} \\ \hline \mathrm{TiCl}_{4} & \text{Ionic} \\ \hline \mathrm{K}_{2}\mathrm{O}_{2} & \text{Ionic} \\ \hline \mathrm{PCl}_{5} & \text{Molecular} \\ \hline \mathrm{P}(\mathrm{OH})_{3} & \text{Molecular} \\ \hline \end{array} \)

Step 1: a) HClO4

: Hydrogen (H), chlorine (Cl), and oxygen (O) are non-metals. As a result, HClO4 is a molecular compound.

Step 2: b) CH3OCH3

: Carbon (C), hydrogen (H), and oxygen (O) are non-metals. Therefore, CH3OCH3 is a molecular compound.

Step 3: c) Mg(NO3)2

: Magnesium (Mg) is a metal, while nitrogen (N) and oxygen (O) are non-metals. Since we have a metal bonded to non-metals, Mg(NO3)2 is an ionic compound.

Step 4: d) H2S

: Hydrogen (H) and sulfur (S) are non-metals. Therefore, H2S is a molecular compound.

Step 5: e) TiCl4

: Titanium (Ti) is a metal, and chlorine (Cl) is a non-metal. Thus, TiCl4 is an ionic compound.

Step 6: f) K2O2

: Potassium (K) is a metal, and oxygen (O) is a non-metal. As a result, K2O2 is an ionic compound.

Step 7: g) PCl5

: Phosphorus (P) and chlorine (Cl) are non-metals. Therefore, PCl5 is a molecular compound.

Step 8: h) P(OH)3

: Phosphorus (P), oxygen (O), and hydrogen (H) are non-metals. Thus, P(OH)3 is a molecular compound.

Key Concepts

Understanding Non-metals

Non-metals are elements that generally lack the properties of metals. They are poor conductors of electricity and heat and have higher electronegativities, meaning they tend to attract electrons in a chemical bond. Non-metals can be found on the right side of the periodic table, and most of them exist as gases or solids under standard conditions.
Common non-metals in chemistry include:

• Hydrogen (H)
• Carbon (C)
• Nitrogen (N)
• Oxygen (O)
• Phosphorus (P)
• Sulfur (S)
• Chlorine (Cl)

These elements often form covalent bonds where they share electrons with other non-metals, resulting in molecular compounds. For example, in compounds like \( ext{H}_2 ext{S} \) and \( ext{PCl}_5 \), all the participating atoms are non-metals, and they form molecules through shared pairs of electrons.

Exploring Metals

Metals are elements known for their malleability, ductility, and excellent conductivity of heat and electricity. Most metals are shiny and solid at room temperature, with only a few exceptions like mercury (Hg) which is liquid. Metals tend to lose electrons to form positive ions in chemical reactions.
Some key metallic elements include:

• Magnesium (Mg)
• Potassium (K)
• Titanium (Ti)

Metals reside mainly on the left side and center of the periodic table. When metals react with non-metals, they often form ions by transferring electrons to non-metals. This process results in ionic compounds. For example, \( ext{Mg(NO}_3 ext{)}_2 \) involves magnesium transferring electrons to nitrogen and oxygen, creating an ionic structure.

Types of Chemical Bonds

Chemical bonds come in different forms, primarily ionic and covalent, depending on the elements involved and their ability to gain, lose, or share electrons.
Ionic bonds occur between metals and non-metals. In this type of bond, metals lose electrons to become positively charged ions, while non-metals gain those electrons to become negatively charged ions. This electron transfer creates an electrostatic attraction between the ions. Compounds such as \( ext{TiCl}_4 \) and \( ext{K}_2 ext{O}_2 \) are examples of ionic compounds, where metals and non-metals form this type of bond.
Covalent bonds generally occur between non-metallic elements. In these bonds, electrons are shared between atoms, allowing each to achieve a stable electron configuration. Such sharing often leads to the formation of molecular compounds. Examples include \( ext{CH}_3 ext{OCH}_3 \) and \( ext{P(OH)}_3 \) where non-metal atoms are bonded through shared electron pairs. Understanding these differences helps predict and explain the properties of various compounds.