Problem 84 - A Complete Resource Book in Chemistry for JEE Main

Question

An atom A has the electronic configuration of \(1 \mathrm{~s}^{2} 2 \mathrm{~s}^{2}\) \(2 \mathrm{p}^{1}\). Atom B has the electronic configuration of \(1 \mathrm{~s}^{2}\) \(2 \mathrm{~s}^{2} 2 \mathrm{p}^{1} .\) The empirical formula of the compound obtained from the reaction of \(\mathrm{A}\) and \(\mathrm{B}\) is (a) \(\mathrm{AB}\) (b) \(\mathrm{AB}_{3}\) (c) \(\mathrm{A}_{3} \mathrm{~B}_{3}\) (d) \(\mathrm{A}, \mathrm{B}_{6}\)

Step-by-Step Solution

Answer

The empirical formula is (a) \(AB\).

Step 1: Determine the Valency of Atom A

The electronic configuration of Atom A is given as \(1s^2 2s^2 2p^1\). This means Atom A has three electrons in its outer shell (\(2s^2 2p^1\)). For main group elements, the number of electrons available for bonding (the valency) is given by the number of electrons that need to be lost, gained, or shared to achieve a full shell. Atom A, with \(2p^1\), can form one bond by sharing its one unpaired electron from the \(2p\) orbital.

Step 2: Determine the Valency of Atom B

The electronic configuration of Atom B is \(1s^2 2s^2 2p^1\). Just like Atom A, Atom B also has three electrons in the outer shell and has one unpaired electron in the \(2p\) orbital. Therefore, Atom B can also form one bond by sharing its one unpaired electron.

Step 3: Determine the Empirical Formula

Both atoms A and B have a valency of one. When two atoms with equal valency combine, they typically form a compound in a 1:1 ratio unless otherwise specified. Therefore, the empirical formula of the compound formed by A and B will be \(AB\).

Step 4: Verify Consistency with Options

From the given options, the empirical formula \(AB\) matches option (a). Thus, the correct answer is \(AB\).

Key Concepts

Valency

Valency is a fundamental concept in chemistry that involves the capability of an atom to bond with other atoms. An atom's valency is determined by the number of electrons in its outermost shell. This is because the valence electrons are the ones involved in bonding. To attain a stable electronic configuration, akin to that of noble gases, atoms will lose, gain, or share electrons.

For instance, if you look at atom A with an electronic configuration of \(1s^2 2s^2 2p^1\), it has three electrons in its second shell. Specifically, the one electron in the \(2p\) orbital is unpaired and can form a bond. Therefore, its valency is one, meaning it can form one chemical bond by sharing this unpaired electron.

• A similar approach applies to atom B with the same electronic configuration. Therefore, both atoms can form one bond correspondingly to their valencies.
• Valency is crucial because it determines how atoms interact with one another in the process of chemical bonding.

Empirical Formula

An empirical formula provides the simplest whole-number ratio of atoms present in a compound. It is extremely useful because it gives a generalized formula that conveys the relative number of each type of atom in the compound.

When determining the empirical formula for a compound involving elements with similar valency, like atoms A and B (both with a valency of one), it typically leads to a 1:1 ratio.

• This means, for every one atom of A, there is one atom of B, resulting in the empirical formula \(AB\).
• This deterministic approach helps deduce not just the ratio in which elements combine but also hints at the underlying bonding patterns.

Understanding empirical formulas allows chemists to quickly comprehend the composition of compounds and predict possible reactions or properties given specific ratios of constituents.

Chemical Bonding

Chemical bonding refers to the connection between atoms that leads to the formation of chemical substances. It is the force that holds atoms together in compounds and molecules. The primary types of chemical bonds are ionic, covalent, and metallic, but our focus here will be primarily on covalent bonding.

When atoms have the same or similar valencies, like atom A and B, they tend to share electrons to achieve stability, forming covalent bonds. In the case of A and B, each has one unpaired electron to share, allowing them to form a single covalent bond.

• Covalent bonding involves the sharing of electron pairs between atoms, allowing them to attain noble gas configurations.
• Such bonds can be quite strong and are important in molecules where atoms need to share electrons to maintain stability.

These interactions are central in forming compounds and determining chemical properties. Chemical bonding thus enables us to predict the structure and reactivity of substances, which is pivotal in many fields of chemistry.