Group 15 and 16 Elements
Nitrogen and oxygen family trends, ammonia, nitric acid, ozone and sulphuric acid. (Chemistry › p-Block Elements, NEET UG syllabus.)
What is Group 15 and 16 Elements?
The reluctance of the outermost s-electrons to participate in bonding, leading to the stability of lower oxidation states for heavier elements in p-block groups.
Key formula / rule: Haber Process (Ammonia synthesis)
Key points
- Describe the general characteristics and trends of Group 15 and 16 elements.
- Explain the anomalous behavior of nitrogen and oxygen.
- Discuss the preparation, properties, and uses of ammonia and nitric acid.
- Explain the allotropic forms of oxygen (ozone) and sulphur.
Common exam trap
Confusing the stability of oxidation states down the group (inert pair effect).
Definitions
- Term
Inert Pair Effect
- Meaning
The reluctance of the outermost s-electrons to participate in bonding, leading to the stability of lower oxidation states for heavier elements in p-block groups.
- Term
Allotropy
- Meaning
The property of some chemical elements to exist in two or more different forms, in the same physical state, known as allotropes. These allotropes have different physical and chemical properties.
- Term
Haber Process
- Meaning
An industrial process for producing ammonia by reacting nitrogen and hydrogen gases at high temperature and pressure in the presence of a catalyst.
- Term
Ostwald Process
- Meaning
An industrial method for the production of nitric acid, involving the catalytic oxidation of ammonia to nitric oxide, followed by further oxidation and absorption in water.
- Term
Contact Process
- Meaning
The primary industrial method for producing sulphuric acid, involving the catalytic oxidation of sulphur dioxide to sulphur trioxide, which is then absorbed in concentrated sulphuric acid to form oleum, followed by dilution.
Learning objectives
Describe the general characteristics and trends of Group 15 and 16 elements.
Explain the anomalous behavior of nitrogen and oxygen.
Discuss the preparation, properties, and uses of ammonia and nitric acid.
Explain the allotropic forms of oxygen (ozone) and sulphur.
Describe the preparation, properties, and uses of sulphuric acid.
Predict the products of reactions involving these elements and their compounds.
Formulae
- Name
Haber Process (Ammonia synthesis)
- Note
Catalyst: Fe/Mo, High P, Moderate T
- Expression
N₂(g) + 3H₂(g) ⇌ 2NH₃(g)
- Name
Ostwald Process (Nitric Acid synthesis)
- Note
Pt/Rh gauze catalyst, 500K, 9 bar. Followed by 2NO(g) + O₂(g) → 2NO₂(g) and 3NO₂(g) + H₂O(l) → 2HNO₃(aq) + NO(g)
- Expression
4NH₃(g) + 5O₂(g) → 4NO(g) + 6H₂O(g)
- Name
Contact Process (Sulphuric Acid synthesis)
- Note
Catalyst: V₂O₅, 720K, 2 bar. Followed by SO₃ + H₂SO₄ → H₂S₂O₇ (oleum) and H₂S₂O₇ + H₂O → 2H₂SO₄
- Expression
2SO₂(g) + O₂(g) ⇌ 2SO₃(g)
Prerequisites
Basic knowledge of periodic table trends (atomic size, ionization enthalpy, electronegativity).
Understanding of chemical bonding (covalent, ionic, multiple bonds, VSEPR theory).
Concepts of oxidation states and redox reactions.
General properties of acids and bases.
Common mistakes
Confusing the stability of oxidation states down the group (inert pair effect).
Incorrectly recalling the industrial preparation processes (Haber, Ostwald, Contact).
Misunderstanding the oxidizing/reducing nature of compounds like HNO₃ and H₂SO₄.
Forgetting the anomalous behavior of the first element in each group.
Not knowing the allotropes of phosphorus and sulphur.
Incorrectly predicting products of reactions with HNO₃ (especially with metals).
Keywords
p-Block
Group 15
Group 16
Nitrogen family
Oxygen family
Ammonia
Nitric acid
Ozone
Sulphuric acid
Haber process
Ostwald process
Contact process
Allotropy
Inert pair effect
Oxidizing agent
Dehydrating agent
Anomalous behavior
Practice preview
What is the shape of the ozone (O₃) molecule?…
easy
Concentrated sulphuric acid acts as a strong dehydrating agent. Which of the following reactions demonstrates this property?…
medium
Which of the following statements is INCORRECT regarding the anomalous behaviour of oxygen compared to other elements of Group 16?…
medium