Oxygen Family (Group-16): Comprehensive NEET Chemistry Notes

1. Introduction to Group-16 (Oxygen Family)

The Oxygen Family, also known as Group-16 or the chalcogens, includes oxygen (O), sulfur (S), selenium (Se), tellurium (Te), and polonium (Po). These elements have six valence electrons with a general electronic configuration of $n{s}^{2}n{p}^4$. The name "chalcogen" is derived from the Greek words for "ore-forming," as many of these elements are commonly found in minerals.

2. Physical Properties of Group-16 Elements

2.1 Atomic and Ionic Radii

As we move down the group from oxygen to polonium, atomic and ionic radii increase due to the addition of electron shells. This reduces the effective nuclear charge on the outermost electrons, making the atoms larger.

2.2 Melting and Boiling Points

Melting and boiling points increase down the group due to stronger van der Waals forces in the heavier elements.

• Oxygen: Exists as diatomic molecules $O_2$ with weak van der Waals forces, giving it low melting and boiling points.
• Sulfur: Exists as polyatomic molecules $S_8$, contributing to higher melting and boiling points.
• Polonium: Exhibits metallic bonding, leading to much higher melting and boiling points than nonmetals and metalloids in the group.

Common Misconception:

Students often think sulfur has lower melting points than oxygen, but due to its larger molecular structure (S₈), it has a higher melting and boiling point.

3. Chemical Properties of Group-16 Elements

3.1 Oxidation States

Group-16 elements exhibit various oxidation states, primarily -2, +4, and +6, due to their ability to expand their octet. Oxygen typically shows a -2 oxidation state, while the heavier elements like sulfur, selenium, and tellurium can exhibit +4 and +6 oxidation states.

• Oxygen: Primarily shows a -2 oxidation state; however, in compounds like $O{F}_2$, it exhibits a +2 state.
• Sulfur, Selenium, Tellurium: Exhibit oxidation states of -2, +4, and +6. Sulfur in sulfuric acid $H_{2}S{O}_4$ is in the +6 state.

3.2 Reactivity with Hydrogen

Group-16 elements form hydrides of the general formula $H_{2}E$ (where E is the Group-16 element). The thermal stability of these hydrides decreases as we move down the group, with water being highly stable and hydrogen telluride being the least stable.

• Oxygen: Forms water $H_{2}O$, a highly stable hydride.
• Sulfur: Forms hydrogen sulfide $H_{2}S$, which is less stable than water and has a characteristic foul smell.
• Tellurium and Polonium: Form unstable hydrides that decompose easily.

Real-life Application:

Hydrogen sulfide (H₂S) is used in qualitative chemical analysis for the detection of metal ions due to its reactivity with various metal salts.

3.3 Reactivity with Oxygen

The Group-16 elements form oxides, and their tendency to form higher oxidation state oxides increases as we go down the group.

• Oxygen: Forms oxides such as $O_2$ and $O_3$ (ozone), with ozone being a powerful oxidizing agent.
• Sulfur: Forms important industrial compounds like sulfur dioxide $S{O}_2$ and sulfur trioxide $S{O}_3$, both of which are precursors to sulfuric acid production.

NEET Problem-Solving Strategy:

When solving oxidation state problems, always check if oxygen is part of a peroxide (where it will have an oxidation state of -1) or is bonded to fluorine (where it can have a positive oxidation state).

4. Electronegativity and Ionization Energy

The electronegativity decreases as we move down the group. Oxygen has the second-highest electronegativity (after fluorine), while polonium has a much lower electronegativity due to its metallic nature.

NEET Tip:

Oxygen's high electronegativity makes it essential for oxidation reactions, such as cellular respiration and combustion.

4.1 Ionization Energy

Ionization energy decreases down the group due to increasing atomic size and decreasing nuclear attraction on the valence electrons.

5. Visual Aids and Diagrams

To enhance understanding, visual aids such as diagrams of molecular structures for $O_2$, $S_8$, and oxides like $S{O}_2$ and $S{O}_3$ should be included. These help in visualizing how bond formation occurs in these elements and their compounds.

6. Quick Recap

• Group-16 elements are called chalcogens and have the electronic configuration $n{s}^{2}n{p}^4$.
• Atomic and ionic radii increase down the group.
• Melting and boiling points increase down the group, with polonium having metallic properties.
• Oxygen shows only a -2 oxidation state, while sulfur and heavier elements can exhibit +4 and +6 oxidation states.
• The stability of hydrides decreases from water to tellurium hydride.
• Electronegativity and ionization energy decrease down the group.

7. NEET Exam Strategy

• Focus on trends like electronegativity, atomic size, and oxidation states for Group-16 questions in NEET.
• Pay attention to common reactions involving sulfur compounds, such as those leading to sulfuric acid production.
• Practice problem-solving strategies for questions involving oxidation states, especially with mixed compounds like peroxides and superoxides.

8. Practice Questions

1. Which element in Group-16 has the highest electronegativity?
   a) Oxygen
   b) Sulfur
   c) Selenium
   d) Polonium
   Solution: a) Oxygen
2. What is the electronic configuration of Group-16 elements?
   a) $n{s}^{2}n{p}^2$
   b) $n{s}^{2}n{p}^4$
   c) $n{s}^{2}n{p}^6$
   d) $n{s}^{2}n{p}^5$
   Solution: b) $n{s}^{2}n{p}^4$
3. Which oxide of sulfur is the key precursor for sulfuric acid production?
   a) $S{O}_2$
   b) $S{O}_3$
   c) $S_2{O}_3$
   d) $SO$
   Solution: b) $S{O}_3$
4. Which of the following hydrides is most thermally stable?
   a) $H_{2}O$
   b) $H_{2}S$
   c) $H_{2}Se$
   d) $H_{2}Te$
   Solution: a) $H_{2}O$
5. What is the oxidation state of sulfur in sulfuric acid ($H_{2}S{O}_4$)?
   a) +2
   b) +4
   c) +6
   d) -2
   Solution: c) +6

9. Supplementary Features

• Glossary:
• • Chalcogens: Elements in Group-16.
  • Oxidation State: The charge of an atom within a compound.
  • Electronegativity: The ability of an atom to attract shared electrons.
• Quick Reference Guide:
• • Electronic Configuration: $n{s}^{2}n{p}^4$
  • Oxidation States: -2, +4, +6
  • Stable Oxides: $S{O}_2$, $S{O}_3$