Question

In the following compound \(\mathrm{H}\) is covalent bonded in case of: (a) \(\mathrm{CaH}_{2}\) (b) \(\mathrm{NaH}\) (c) \(\mathrm{SiH}_{4}\) (d) \(\mathrm{BaH}_{2}\)

Short answer

Hydrogen forms covalent bonds in SiH_{4} .

Step-by-step solution

Understand Covalent Bonds

Covalent bonds occur when atoms share electrons, typically between nonmetals or elements with similar electronegativities. Hydrogen forms covalent bonds when paired with nonmetals.

Analyze Compounds

Examine the given compounds to identify whether hydrogen forms covalent bonds. In ionic hydrides, hydrogen bonds with metals in which electrons are transferred rather than shared.

Identify Covalent Compound Among Options

For each compound, check the elements involved: - CaH_{2} and BaH_{2} have hydrogen with metals that form ionic bonds due to electron transfer. - NaH is formed with sodium, a metal also forming ionic hydride. - SiH_{4} has silicon with hydrogen, forming covalent bonds due to similar electronegativities between silicon (a nonmetal) and hydrogen.

Select Correct Compound

Based on the analysis, SiH_{4} is the compound where hydrogen forms covalent bonds due to sharing electrons with a nonmetal (silicon).

Key concepts

Covalent Bonds

Covalent bonds are like chemistry’s way of giving a hug. These bonds happen when two atoms meet and decide to share their electrons. This sharing lets them reach a stable state and forms a strong bond.
Atoms that form covalent bonds are often nonmetals. They usually have similar electronegativities, meaning they have a similar pull on the electrons in their shared orbit. This prevents one atom from pulling the shared electrons away from the other, creating a balanced sharing.
Covalent bonds can occur between same or different elements as long as they are nonmetals. This is important when determining the nature of a bond in compounds like hydrides. For example, hydrogen in SiH_{4} forms covalent bonds because both hydrogen and silicon have similar electronegativities, allowing for an even sharing of electrons.

Ionic Bonds

Ionic bonds occur when one atom gives up one or more electrons to another atom. This usually happens between metals and nonmetals. Metals, having fewer electrons in their outer shell, tend to lose them easily, becoming positively charged ions. Nonmetals, on the other side, readily accept these electrons, becoming negatively charged ions. This transfer of electrons results in two oppositely charged ions which attract each other, forming an ionic bond.
Ionic bonds are notably different from covalent bonds. They arise from full electron transfers rather than sharing. Take compounds like CaH_{2} and BaH_{2} —they involve metals and hydrogen, indicating ionic bonds. Here, the metal donates electrons to hydrogen, making these ionic hydrides.

Nonmetals

Nonmetals are elements that usually make covalent bonds due to their high electronegativity. They don’t give up electrons easily but prefer sharing them when necessary. Most nonmetals have properties like high ionization energies and low electrical conductivity.
Hydrides can be covalent or ionic depending on whether they are paired with a nonmetal or a metal, respectively. For example, in SiH_{4} , hydrogen is bonded to silicon, a nonmetal, leading to covalent bonding. This partnership leads to a strong sharing relationship due to their similarities in electronegativity. Typically, understanding the characteristics of nonmetals helps determine the type of bonds they will form and ultimately, the nature of the compound.

Electronegativity

Electronegativity is an atom’s ability to attract and hold onto electrons within a chemical bond. It is a vital concept when we discuss why certain bonds are either covalent or ionic. When two atoms in a molecule have similar electronegativities, they share electrons equally, leading to covalent bonding. This happens because neither atom has a significantly stronger pull on the electrons than the other.
In hydrides like SiH_{4} , both hydrogen and silicon have relatively similar electronegativities. This results in covalent hydrides thanks to their balanced sharing. However, if an atom has very different electronegativity from hydrogen—like metals do in NaH or CaH_{2} —the bond becomes ionic, as electrons are primarily transferred rather than shared. Understanding electronegativity helps predict bond types and their respective characteristics.