Problem 97 - A Complete Resource Book in Chemistry for JEE Main

Question

In case of the oxygen family (group 16) (a) the tendency for catenation decreases markedly as we go down the group (b) maximum coordination of oxygen is four due to lack of d orbital, but that of other elements is six due to presence of d orbitals (c) the tendency to form multiple bonds with \(\mathrm{C}, \mathrm{N}\) and O decreases as going down the group from \(\mathrm{S}\) to Te (d) all are correct

Step-by-Step Solution

Answer

All statements (a), (b), and (c) are correct; hence, (d) is the right choice.

Step 1: Understanding Catenation Tendency

Catenation refers to the ability of an element to form bonds with itself, forming chains or rings. In group 16, the tendency for catenation decreases down the group because the bond energy of the element-element bonds decreases due to increasing atomic size and decreasing overlapping of orbitals.

Step 2: Coordination Number of Group 16 Elements

Oxygen has a maximum coordination number of four because it lacks d orbitals. For other elements in group 16, the presence of d orbitals allows them to expand their valence shell and thus can have a coordination number up to six.

Step 3: Tendency for Multiple Bond Formation

Oxygen, sulfur, and other elements in group 16 can form multiple bonds. However, the ability to form multiple bonds with elements like carbon, nitrogen, and oxygen decreases as we move down the group from sulfur to tellurium. This is due to the increasing size and decreasing p-orbital lateral overlap.

Step 4: Evaluating Correct Statement

Based on the analysis, statements (a), (b), and (c) are accurate descriptions of the properties of group 16 elements. Therefore, option (d), "all are correct," represents the correct answer.

Key Concepts

Catenation Tendency

Catenation is the capability of an element to form bonds with itself, creating long chains or ring structures. In the oxygen family, or group 16 elements, this property diminishes as you move down the group. Oxygen, being a smaller atom, has a pronounced ability to form O-O bonds. However, as elements become larger down the group—like sulfur (S), selenium (Se), tellurium (Te), and polonium (Po)—their atoms have larger radii. Because of this larger size:

• The overlap between atomic orbitals is reduced.
• The strength of element-element bonds is weaker.
• As a result, the tendency for catenation decreases.

Children in chemistry might find it fun to think of catenation as elements "holding hands". However, as hands get bigger down the group, they find it harder to "hold" firmly, therefore preferring other elements for bonding.

Coordination Number

The coordination number refers to the number of bonds an atom can form. In group 16 elements, the ability for different coordination numbers depends on the availability of orbitals for bonding. Oxygen is special—since it lacks d orbitals, it can only form up to four bonds. For example:

• It can form water (H₂O), which has two bonds and two lone pairs.
• In the ozone (O₃) molecule, each oxygen is typically linked with others forming a simple triatomic molecule.

The situation changes with elements like sulfur and selenium. They possess d orbitals, allowing them to make more room for bonds, resulting in a higher coordination number, going as high as six.

Multiple Bond Formation

Group 16 elements can form multiple bonds, but this capacity diminishes as you proceed down the group. Oxygen is famous for its ability to engage in multiple bonding, forming double bonds as seen in:

• Carbon dioxide (CO₂) where each carbon-oxygen bond is a double bond.
• Nitric oxide (NO) where the oxygen forms a double bond with nitrogen.

As we move down to sulfur, selenium, and tellurium, the larger atomic size prevents such efficient overlap in p-orbitals. This attribute results in a decreased likelihood of forming multiple bonds. This phenomenon doesn't just make it difficult for these elements to form multiple bonds, it's a critical concept to understand how these elements behave chemically.

Group 16 Elements

The oxygen family, or chalcogens, belongs to group 16 of the periodic table. This group includes:

• Oxygen (O)
• Sulfur (S)
• Selenium (Se)
• Tellurium (Te)
• Polonium (Po)

Each of these elements shares similar properties, thanks to having six valence electrons. This means they typically need two more electrons to complete their valence shell—hence, they often exhibit a -2 oxidation state. From supporting life on Earth through oxygen to being industrially crucial in sulfur compounds, these elements are incredibly versatile. Note the progression in properties like electronegativity and atomic size as you move down the group, impacting their chemical behavior.

d Orbitals

d Orbitals play a key role in the chemistry of heavier group 16 elements. While oxygen does not have d orbitals in its valence shell, elements like sulfur, selenium, and tellurium do. This presence allows these elements to "expand" their valence shells beyond the typical octet, accommodating more electrons, and therefore, forming more complex compounds or higher coordination states.

• This expansion capability allows them to reach coordination numbers of up to six.
• It facilitates diverse chemical bonding, contributing to the element’s ability to interact in more intricate chemical processes.

d Orbitals introduce fascinating chemistry, explaining why these elements possess unique properties and capabilities, distinct from oxygen's simple 2p orbital chemistry.