Question

Regarding covalent hydrides, which of the following statement is wrong? (1) They are formed by elements of high electronegativity. (2) They are formed by the $p$ -block elements due to sharing of electrons with hydrogen. (3) They have low melting and boiling points and do not conduct electricity. (4) They cannot act as reducing agents.

Short answer

Statement (4) is wrong.

Step-by-step solution

Analyze Statement (1)

Covalent hydrides are indeed formed by elements of high electronegativity. Examples include hydrogen compounds with elements like fluorine, oxygen, and nitrogen. Thus, statement (1) is correct.

Examine Statement (2)

Covalent hydrides are commonly formed by the sharing of electrons between hydrogen and the p-block elements (e.g., methane, ammonia). Therefore, statement (2) is also correct.

Consider Statement (3)

Covalent hydrides typically have low melting and boiling points, and they do not conduct electricity because they do not have free ions or electrons. Thus, statement (3) is correct.

Evaluate Statement (4)

Many covalent hydrides can act as reducing agents. For instance, methane can undergo combustion and reduce other compounds. Therefore, statement (4) is incorrect.

Key concepts

Electronegativity

Electronegativity is the tendency of an atom to attract electrons in a chemical bond. In covalent hydrides, elements with high electronegativity tend to form stronger bonds with hydrogen. Electronegativity is a crucial factor in determining the bond characteristics and stability of these hydrides. For example, fluorine, oxygen, and nitrogen have high electronegativities and form stable covalent hydrides like hydrogen fluoride (HF), water (H2O), and ammonia (NH3). Covalent hydrides formed with high electronegativity elements generally exhibit polar bonds due to the uneven distribution of electron density.

p-block elements

The p-block elements are found in groups 13 to 18 of the periodic table. These elements, which include carbon, nitrogen, oxygen, and fluorine, commonly form covalent hydrides. p-block elements achieve stable electron configurations by sharing electrons with hydrogen. For instance, methane (CH4) involves carbon (a p-block element) sharing electrons with hydrogen. The chemical properties of p-block elements facilitate the formation of various covalent hydrides, impacting their stability, reactivity, and overall behavior in chemical reactions.

Reducing agents

Reducing agents are substances that can donate electrons to other molecules, thereby reducing them. Many covalent hydrides, such as methane and ammonia, act as reducing agents. When methane (CH4) undergoes combustion, it reduces oxygen and forms carbon dioxide and water. Similarly, ammonia (NH3) can reduce metal oxides in various chemical processes. The reducing ability of covalent hydrides is pivotal in many industrial and chemical reactions, including metal extraction and organic synthesis. This property is intrinsic to the chemical nature of hydrogen and its ability to form strong bonds with other elements.

Physical properties of covalent hydrides

Covalent hydrides generally exhibit low melting and boiling points due to weak intermolecular forces, such as van der Waals forces or dipole-dipole interactions. Additionally, these hydrides do not conduct electricity because they lack free ions or electrons. For instance, compounds like methane (CH4) and water (H2O) have relatively low boiling points compared to ionic or metallic compounds. Furthermore, due to their non-conductive nature, covalent hydrides are poor conductors of electricity, making them suitable for use as insulators in certain applications.