Problem 39 - Chemistry The Molecular Science

Question

Predict which compounds are ionic. Explain your answers. (a) \(\mathrm{NaH}\) (b) \(\mathrm{HCl}\) (c) \(\mathrm{NH}_{3}\) (d) \(\mathrm{CH}_{4}\) (e) HI

Step-by-Step Solution

Answer

Only \(\mathrm{NaH}\) is ionic; others are covalent.

Step 1: Understand Compound Types

Compounds are classified based on the types of bonds they contain: ionic or covalent. Ionic compounds typically consist of metals and non-metals, where electrons are transferred from the metal to the non-metal. Covalent compounds comprise only non-metals, where electrons are shared.

Step 2: Analyze Sodium Hydride ( \( \mathrm{NaH} \) )

Sodium (\(\mathrm{Na}\)) is a metal, and hydrogen (\(\mathrm{H}\)), while non-metal, behaves as an anion here. The bond between them is ionic as sodium donates an electron to hydrogen.

Step 3: Analyze Hydrogen Chloride ( \( \mathrm{HCl} \) )

Both hydrogen (\(\mathrm{H}\)) and chlorine (\(\mathrm{Cl}\)) are non-metals. They share electrons, forming a covalent bond. Hence, \(\mathrm{HCl}\) is not ionic.

Step 4: Analyze Ammonia ( \( \mathrm{NH}_{3} \) )

Nitrogen (\(\mathrm{N}\)) and hydrogen (\(\mathrm{H}\)) are both non-metals. The electrons are shared among them, forming covalent bonds. Therefore, \(\mathrm{NH}_{3}\) is not ionic.

Step 5: Analyze Methane ( \( \mathrm{CH}_{4} \) )

Carbon (\(\mathrm{C}\)) and hydrogen (\(\mathrm{H}\)) are both non-metals, and they share electrons in covalent bonds. Thus, \(\mathrm{CH}_{4}\) is not ionic.

Step 6: Analyze Hydrogen Iodide ( \( \mathrm{HI} \) )

Hydrogen (\(\mathrm{H}\)) and iodine (\(\mathrm{I}\)) are both non-metals. Their bond is covalent because they share electrons. Hence, \(\mathrm{HI}\) is not ionic.

Key Concepts

Ionic Bonds

Ionic bonds are a type of chemical bond where electrons are transferred from one atom to another. This typically occurs between metals and non-metals. In these bonds:

• Metals, which have few electrons in their outer shell, lose electrons to achieve a stable electron configuration. They become positively charged ions, known as cations.
• Non-metals, which have more electrons in their outer shell, gain these electrons to complete their valence shell, resulting in negatively charged ions, known as anions.

The attraction between the positive and negative ions forms a very strong bond. For example, in sodium hydride (\(\mathrm{NaH}\)), sodium donates an electron to hydrogen, resulting in an ionic bond.

Covalent Bonds

Covalent bonds are formed when two atoms share electrons. This usually happens between non-metal elements. In these bonds:

• Atoms strive to achieve a full outer electron shell, similar to noble gases, by sharing electrons.
• The shared electrons allow each atom to attain the electron configuration of a noble gas, creating a stable molecule.

Covalent bonding can be found in a variety of molecules like water (\(\mathrm{H}_2\mathrm{O}\)), hydrogen chloride (\(\mathrm{HCl}\)), and ammonia (\(\mathrm{NH}_3\)), where non-metal atoms share pairs of electrons to form stable compounds.

Chemical Bonding

Chemical bonding is the mechanism by which atoms combine to form compounds. It can involve either the sharing or transferring of outer (valence) electrons:

• Ionic bonding: Involves transfer of electrons, leading to the creation of ions (charged particles). It typically occurs between metals and non-metals.
• Covalent bonding: Involves sharing electrons and is common between non-metal atoms.

The strength and type of chemical bond determine the properties of the compound. For instance, ionic compounds typically form crystalline solids and have high melting and boiling points, while covalent compounds can be gases, liquids, or solids with lower melting and boiling points.

Compound Classification

Compounds are classified based on the type of bonding between their atoms. This classification helps in understanding the chemical and physical properties of a compound.

• Ionic Compounds: Formed through ionic bonds, usually between metals and non-metals. They tend to be hard, brittle, and have high melting and boiling points.
• Covalent Compounds: Formed through covalent bonds, usually among non-metals. They can vary widely in physical state—gases, liquids, or solids—and typically have lower melting and boiling points.

Accurately classifying a compound helps in predicted its behavior in chemical reactions and its interactions with other substances, which is fundamental for many fields such as pharmacology, materials science, and environmental chemistry.