Question

Which of the following statements are true? (a) Both nitrogen and phosphorus can form a pentafluo- ride compound.(b) Si can form three stable compounds containing two Si atoms each, \(\mathrm{Si}_{2} \mathrm{H}_{2}, \mathrm{Si}_{2} \mathrm{H}_{4},\) and \(\mathrm{Si}_{2} \mathrm{H}_{6}\) (c) \(\mathrm{Cl}_{2}\) is easier to oxidize than \(\mathrm{I}_{2}\) (d) At room temperature, the stable form of oxygen is \(\mathrm{O}_{2}\) , whereas that of sulfur is \(\mathrm{S}_{8} .\)

Short answer

Only statement (d) is true, which states that at room temperature, the stable form of oxygen is \(\mathrm{O}_{2}\), and that of sulfur is \(\mathrm{S}_{8}\). Statements (a), (b), and (c) are false.

Step-by-step solution

Statement (a) Analysis

To verify if both nitrogen and phosphorus can form a pentafluoride compound, we need to look at their valency and if they can bond with five fluorine atoms. Nitrogen is in group 15 and has a valency of 3 and phosphorus is in group 15 and has a valency of 5.

Statement (a) Conclusion

Nitrogen forms \(\mathrm{NF}_{3}\), but it cannot form pentafluoride \(\mathrm{NF}_{5}\) due to its lower valency. However, phosphorus can form \(\mathrm{PF}_{5}\), as it has a valency of 5. Therefore, statement (a) is False.

Statement (b) Analysis

In this statement, we need to verify if Si can form the specified stable compounds: \(\mathrm{Si}_{2} \mathrm{H}_{2}, \mathrm{Si}_{2} \mathrm{H}_{4},\) and \(\mathrm{Si}_{2} \mathrm{H}_{6}\). Silicon is in group 14 and has a valency of 4.

Statement (b) Conclusion

Silicon can form stable compounds with hydrogen, but the given compounds are not correct. The actual compounds are \(\mathrm{SiH}_{4}\) (silane), \(\mathrm{Si}_{2} \mathrm{H}_{6}\) (disilane), and \(\mathrm{Si}_{3} \mathrm{H}_{8}\) (trisilane). So, statement (b) is False.

Statement (c) Analysis

To verify if \(\mathrm{Cl}_{2}\) is easier to oxidize than \(\mathrm{I}_{2}\), we need to consider the electronegativity of both elements and their ability to gain electrons.

Statement (c) Conclusion

Chlorine is more electronegative than iodine. Thus, the electron affinity of chlorine is more than iodine. This means that chlorine will gain electrons more easily compared to iodine. So, iodine is easier to oxidize than chlorine. Hence, statement (c) is False.

Statement (d) Analysis

In this statement, we need to verify the stable forms of oxygen and sulfur at room temperature. Oxygen is in group 16 and has a valency of 2, and sulfur is also in group 16 but has a valency of 6.

Statement (d) Conclusion

At room temperature, the stable form of oxygen is \(\mathrm{O}_{2}\), which is a diatomic molecule. Sulfur exists as an octatomic molecule, \(\mathrm{S}_{8}\), forming a crown-shaped structure. So, statement (d) is True. In conclusion, only statement (d) is true, whereas statements (a), (b), and (c) are false.

Key concepts

Valency of Elements

Valency is a fundamental concept in chemistry that describes the ability of an atom to combine with other atoms. It indicates the number of electrons an atom can lose, gain, or share to form a stable compound. The valency of elements is largely determined by their position in the periodic table, specifically by the number of electrons in their outer shell. For instance, nitrogen, located in group 15 of the periodic table, has a valency of 3 because it has five electrons in its outer shell and needs three more to complete the octet. On the other hand, phosphorus, also in group 15, tends to show a valency of 5, as it can utilize d-orbitals for bonding in addition to its p-orbitals, allowing it to form PF5.

Understanding valency is crucial when predicting the types of compounds an element can form. For example, the inability of nitrogen to form NF5 is due to its limited valency, in contrast to the higher valency of phosphorus that allows for such a compound. Needless to say, the concept of valency simplifies the understanding of molecular structure and the rules of chemical bonding.

Stability of Compounds

The stability of compounds is inherently connected to the concept of valency, as it involves the complete filling of an atom's outer electron shell. Stability is the tendency of a compound to resist decomposition or chemical change. Stable compounds are usually formed when atoms achieve a noble gas configuration, either by losing, gaining, or sharing electrons to complete their valence shell. For instance, silicon, with a valency of 4, can form stable compounds with hydrogen such as SiH4 (silane).

The formation of stable molecules like O2 and S8 can be understood through the concept of atomic valency and molecular geometry. Oxygen atom pairs share two pairs of electrons to form O2, resulting in a stable double bond. Sulfur atoms, however, bond with each other in an intricate crown-shaped S8 molecule, demonstrating the complexity that arises in multi-atom molecules. Therefore, the structure and stability are interconnected, influencing physical properties and reactivity of substances.

Oxidation States

The oxidation state, also known as oxidation number, denotes the degree of oxidation of an atom in a chemical compound. This concept is essential in understanding redox reactions, where transfer of electrons occurs. The oxidation state of an atom is the charge it would have if the compound was composed of ions. Typically, elements with higher electronegativity (like chlorine) have negative oxidation states since they attract electrons strongly, while elements with lower electronegativity (like iodine) have positive oxidation states.

Chlorine has a high tendency to accept electrons (high electronegativity), indicating less likelihood of being oxidized. Conversely, iodine's lower electronegativity makes it more prone to oxidation, as seen in statement (c) of the exercise. By comprehending oxidation states, one can predict the reactivity and the outcomes of chemical reactions, greatly simplifying the study of inorganic chemistry and various biological processes where oxidation and reduction play a vital role.