Question

Which compounds are considered to be binary covalent hydrides? (a) \(\mathrm{MgH}_{2}, \mathrm{SrH}_{2}, \mathrm{AlH}_{3}, \mathrm{SiH}_{4}\) (b) \(\mathrm{BeH}_{2}, \mathrm{~B}_{2} \mathrm{H}_{6}, \mathrm{CH}_{4}, \mathrm{NH}_{3}\) (c) \(\mathrm{MgH}_{2}, \mathrm{AlH}_{3}, \mathrm{SiH}_{4}, \mathrm{H}_{2} \mathrm{~S}\) (d) \(\mathrm{NaH}, \mathrm{KH}, \mathrm{CaH}_{2}, \mathrm{BaH}_{2}\)

Short answer

(b) is the correct answer, containing binary covalent hydrides.

Step-by-step solution

- Define a binary covalent hydride

Binary covalent hydrides are compounds consisting of hydrogen and a nonmetal. They are typically formed when hydrogen bonds with nonmetals such as carbon, silicon, nitrogen, etc. These compounds exhibit covalent bonding rather than ionic bonding.

- Analyze the compounds in each option

For each option, identify which elements hydrogen is bonded with and determine whether these elements are nonmetals (indicating a covalent bond):- (a) \( \mathrm{SiH}_{4} \) is a candidate since silicon (\( \mathrm{Si} \)) is a nonmetal.- (b) \( \mathrm{CH}_{4} \) and \( \mathrm{NH}_{3} \) are candidates because carbon (\( \mathrm{C} \)) and nitrogen (\( \mathrm{N} \)) are nonmetals.- (c) \( \mathrm{SiH}_{4} \) is again a candidate because it involves a nonmetal.- (d) All elements bonded with hydrogen are metals, indicating these are ionic hydrides.

- Determine correct answers based on analysis

Based on the analysis of each compound:- Option (a) includes \( \mathrm{SiH}_{4} \), which is a binary covalent hydride.- Option (b) includes \( \mathrm{CH}_{4} \) and \( \mathrm{NH}_{3} \), both are binary covalent hydrides.- Option (c) includes \( \mathrm{SiH}_{4} \), meeting the criteria for binary covalent hydrides.- Option (d) does not include any binary covalent hydrides as all compounds are metallic hydrides.

Key concepts

Covalent Bonding

Covalent bonding is a type of chemical bonding where pairs of electrons are shared between atoms. This happens primarily between nonmetals. Unlike ionic bonds, where electrons are transferred, covalent bonds involve the sharing of electrons to achieve a stable electron configuration. This sharing of electrons allows both atoms involved to satisfy the octet rule by filling their outer electron shells.

Here are some key features of covalent bonding:

• Covalent bonds typically form between nonmetal atoms.
• The strength of the bond is related to the number of shared electron pairs.
• Covalent compounds can be gases, liquids, or solids at room temperature.
• They often have lower melting and boiling points compared to ionic compounds.

When discussing binary covalent hydrides, these compounds specifically involve hydrogen forming a covalent bond with another nonmetal.

Hydrogen Compounds

Hydrogen is a unique element that can form compounds with almost all other elements. In binary hydrides, hydrogen is paired with one other element. These compounds can be classified based on the type of element hydrogen bonds with, such as metals or nonmetals.

Binary covalent hydrides are particularly important because they feature useful interactions between hydrogen and nonmetals. For instance:

• Methane \(\mathrm{CH}_4\): Hydrogen bonds with carbon, creating a simple hydrocarbon essential for energy processes.
• Ammonia \(\mathrm{NH}_3\): Hydrogen bonds with nitrogen, forming a compound vital for fertilizers and cleaning agents.
• Silane \(\mathrm{SiH}_4\): Hydrogen bonds with silicon, used in the electronics industry for silicon-based semiconductors.

Understanding hydrogen compounds helps in recognizing their applications and significance in industry and daily life.

Nonmetals

Nonmetals are elements typically found on the right side of the periodic table and are essential for forming covalent bonds with hydrogen. They have high electronegativities, meaning they tend to attract electrons more than metals do. This property allows them to share electrons effectively, making them key participants in covalent bonding.

Some characteristics of nonmetals include:

• They often have high ionization energies and electron affinities.
• They can exist in various states of matter: gases (like nitrogen), liquids (like bromine), and solids (like carbon).
• Nonmetals like carbon, nitrogen, oxygen, and silicon are crucial for forming a wide variety of binary covalent hydrides.

These elements are central to many biological and chemical processes on Earth, contributing to compounds that are fundamental to life and technology.

Chemical Bonding Types

Chemical bonding types describe how atoms interact and connect to form chemical substances. The primary types of chemical bonds include covalent, ionic, and metallic bonds. Understanding these helps in predicting the properties and behaviors of compounds.

• Ionic Bonds: These occur between metals and nonmetals. They involve the transfer of electrons, forming ions, and result in high melting and boiling points.
• Covalent Bonds: These occur between nonmetals. They involve sharing electrons, as seen in binary covalent hydrides.
• Metallic Bonds: These occur between metal atoms. They involve a 'sea of electrons' moving freely, accounting for metals' conductive properties.

Understanding these types of bonding allows us to grasp why certain substances have specific physical and chemical properties. For instance, covalent compounds are generally more versatile but may conduct electricity poorly compared to metallic or ionic compounds.