Non-Metals in Chemistry

This comprehensive lesson covers the key concepts, properties, and reactions of non-metals as required by the CXC Chemistry syllabus for 2024-2025.

Introduction to Non-Metals

Non-metals are elements that generally lack the physical and chemical properties of metals. They are located on the right side of the periodic table and make up the majority of elements in Groups 14-17 (IV-VII).

Position of Non-Metals in the Periodic Table METALS NON-METALS Group 14-17 (IV-VII) C, N, O, F, P, S, Cl, Br, I Noble Gases He, Ne, Ar, Kr, Xe, Rn

General Characteristics of Non-Metals

Non-Metals in the Periodic Table

The non-metals are found on the right side of the periodic table and include:

Group Non-Metal Elements Key Properties
Group 14 (IV) Carbon (C) Forms allotropes (diamond, graphite, fullerenes); basis of organic chemistry
Group 15 (V) Nitrogen (N), Phosphorus (P) Form covalent compounds; essential for life processes
Group 16 (VI) Oxygen (O), Sulfur (S), Selenium (Se) Typically form -2 ions; reactive with metals
Group 17 (VII) Fluorine (F), Chlorine (Cl), Bromine (Br), Iodine (I) Halogens; highly reactive; form -1 ions
Group 18 (VIII) Helium (He), Neon (Ne), Argon (Ar), Krypton (Kr), Xenon (Xe), Radon (Rn) Noble gases; chemically inert (full valence shells)

Key Non-Metals and Their Properties

Carbon (C)

Group 14 (IV), Period 2
Physical State: Solid
Allotropes: Diamond, Graphite, Fullerenes

Key Properties:

Diamond (3D tetrahedral structure) Graphite (layered structure)

Nitrogen (N)

Group 15 (V), Period 2
Physical State: Gas
Molecular Form: N₂ (triple bond)

Key Properties:

Oxygen (O)

Group 16 (VI), Period 2
Physical State: Gas
Molecular Form: O₂ (double bond)
Allotropes: O₂ (oxygen), O₃ (ozone)

Key Properties:

Sulfur (S)

Group 16 (VI), Period 3
Physical State: Solid
Allotropes: Rhombic sulfur (S₈ rings), monoclinic sulfur

Key Properties:

S₈ Ring Structure

Halogens (Group 17/VII)

Halogens include Fluorine (F), Chlorine (Cl), Bromine (Br), and Iodine (I).

Physical States:
  • F₂, Cl₂: Gases
  • Br₂: Liquid
  • I₂: Solid

Key Properties:

F₂ Pale Yellow Gas Cl₂ Green-Yellow Gas Br₂ Red-Brown Liquid I₂ Purple-Black Solid

Noble Gases (Group 18/VIII)

Noble gases include Helium (He), Neon (Ne), Argon (Ar), Krypton (Kr), Xenon (Xe), and Radon (Rn).

Key Properties:

Chemical Reactions of Non-Metals

Reactions with Oxygen

Examples:

Simple Experiment: Combustion of Sulfur

Materials: Spoon, sulfur powder, Bunsen burner, beaker with water, litmus paper/universal indicator

Procedure:

  1. Place some sulfur powder in a deflagrating spoon
  2. Heat the sulfur until it ignites (blue flame)
  3. Cover the burning sulfur with a beaker containing a small amount of water
  4. Observe the formation of sulfur dioxide gas
  5. After the reaction, test the water with litmus paper or universal indicator

Observations:

Reactions:

Reactions with Hydrogen

Examples:

Reactions with Metals

Examples:

Reactions between Non-Metals

Examples:

Industrial and Biological Importance of Non-Metals

Carbon

Nitrogen

Oxygen

Sulfur

Halogens

Noble Gases

Environmental Impact of Non-Metals

Carbon Dioxide (CO₂)

Sulfur Dioxide (SO₂)

Nitrogen Oxides (NOₓ)

Ozone (O₃)

Extraction and Purification of Non-Metals

Oxygen

Nitrogen

Sulfur

Frasch Process for Sulfur Extraction Sulfur Deposit Compressed Air Superheated Water Liquid Sulfur 1. Superheated water melts sulfur 2. Compressed air forces liquid sulfur up 3. Liquid sulfur is collected at surface

Chlorine

Tests for Non-Metals and Their Compounds

Carbon Dioxide (CO₂)

Hydrogen (H₂)

Oxygen (O₂)

Chlorine (Cl₂)

Ammonia (NH₃)

Hydrogen Sulfide (H₂S)

Important Compounds of Non-Metals

Compounds of Carbon

Compound Formula Properties Uses
Carbon Dioxide CO₂ Colorless gas, slightly acidic in water Carbonated drinks, fire extinguishers, photosynthesis
Carbon Monoxide CO Colorless, odorless toxic gas Industrial reducing agent, component of synthesis gas
Methane CH₄ Colorless gas, main component of natural gas Fuel, production of hydrogen and other chemicals

Compounds of Nitrogen

Compound Formula Properties Uses
Ammonia NH₃ Colorless gas with pungent smell, very soluble in water Fertilizer production, cleaning products, refrigerant
Nitric Acid HNO₃ Colorless to yellow liquid, strong acid Fertilizer production, explosives, metal etching
Nitrogen Dioxide NO₂ Reddish-brown gas, toxic Intermediate in nitric acid production, air pollutant

Compounds of Sulfur

Compound Formula Properties Uses
Sulfuric Acid H₂SO₄ Dense, colorless oily liquid, strong dehydrating agent Car batteries, fertilizer production, chemical manufacturing
Sulfur Dioxide SO₂ Colorless gas with pungent odor Food preservative, bleaching agent, sulfuric acid production
Hydrogen Sulfide H₂S Colorless gas with rotten egg smell, toxic Analytical chemistry, metallurgical processes

Compounds of Halogens

Compound Formula Properties Uses
Hydrogen Chloride HCl Colorless gas, forms hydrochloric acid in water Metal cleaning, food processing, chemical manufacturing
Sodium Chloride NaCl White crystalline solid, highly soluble in water Food seasoning, chemical manufacturing, water softening
Chlorofluorocarbons CFCs Volatile derivatives with chlorine and fluorine Previously used as refrigerants (now restricted due to ozone depletion)

Periodic Trends in Non-Metals

Across the Period (Left to Right)

Down the Group

Trends in Non-Metal Properties Electronegativity Increases → Decreases ↓ Atomic Radius ← Decreases Increases ↓ Ionization Energy Increases → Decreases ↑

Glossary of Terms

Self-Assessment Questions

1. Which of the following is NOT a characteristic of most non-metals?

  1. Poor conductors of heat and electricity
  2. Usually brittle in solid state
  3. Generally form acidic oxides
  4. High melting and boiling points

d. High melting and boiling points

Most non-metals have low melting and boiling points (except diamond), while metals typically have high melting and boiling points.

2. Which group in the periodic table contains elements that exist as diatomic molecules?

  1. Group 1 (I)
  2. Group 14 (IV)
  3. Group 17 (VII)
  4. Group 18 (VIII)

c. Group 17 (VII)

The halogens in Group 17 (F₂, Cl₂, Br₂, I₂) exist as diatomic molecules in their elemental state.

3. Which allotrope of carbon is an electrical conductor?

  1. Diamond
  2. Graphite
  3. Both diamond and graphite
  4. Neither diamond nor graphite

b. Graphite

Graphite can conduct electricity due to its delocalized electrons, while diamond is an electrical insulator.

4. When a non-metal oxide dissolves in water, what type of solution is typically formed?

  1. Acidic solution
  2. Basic solution
  3. Neutral solution
  4. Amphoteric solution

a. Acidic solution

Non-metal oxides are generally acidic and form acids when dissolved in water (e.g., CO₂ + H₂O → H₂CO₃; SO₂ + H₂O → H₂SO₃).

5. Which of the following elements has the highest electronegativity?

  1. Carbon
  2. Nitrogen
  3. Oxygen
  4. Fluorine

d. Fluorine

Fluorine has the highest electronegativity of all elements in the periodic table.

6. What gas turns limewater milky?

  1. Oxygen
  2. Nitrogen
  3. Carbon dioxide
  4. Hydrogen

c. Carbon dioxide

Carbon dioxide reacts with limewater (calcium hydroxide solution) to form calcium carbonate precipitate, which gives a milky appearance: Ca(OH)₂ + CO₂ → CaCO₃ + H₂O

7. Which process is used for the extraction of sulfur from underground deposits?

  1. Frasch process
  2. Contact process
  3. Haber process
  4. Ostwald process

a. Frasch process

The Frasch process uses superheated water to melt underground sulfur, which is then forced to the surface using compressed air.

8. What is the gas produced when dilute hydrochloric acid reacts with a metal?

  1. Oxygen
  2. Carbon dioxide
  3. Chlorine
  4. Hydrogen

d. Hydrogen

When dilute hydrochloric acid reacts with a metal, hydrogen gas is produced: 2HCl + Mg → MgCl₂ + H₂

9. As you move from left to right across a period in the periodic table, what happens to the atomic radius of elements?

  1. Increases
  2. Decreases
  3. Remains constant
  4. Increases then decreases

b. Decreases

As you move from left to right across a period, the atomic radius generally decreases due to increased nuclear charge pulling electrons closer to the nucleus.

10. Which non-metal is essential for the production of proteins in living organisms?

  1. Carbon
  2. Oxygen
  3. Sulfur
  4. Nitrogen

d. Nitrogen

Nitrogen is an essential component of amino acids, which are the building blocks of proteins.

Extended Response Questions

1. Compare and contrast the physical and chemical properties of metals and non-metals. Include specific examples to illustrate your points.

Physical Properties:

Metals:

  • Generally solid at room temperature (except mercury)
  • Good conductors of heat and electricity
  • Malleable and ductile
  • High melting and boiling points
  • Lustrous appearance
  • Examples: Iron (solid, shiny, conducts electricity, melting point 1538°C)

Non-metals:

  • Exist in all three states at room temperature
  • Poor conductors of heat and electricity (except graphite)
  • Brittle in solid state
  • Generally low melting and boiling points
  • Dull appearance (except iodine)
  • Examples: Sulfur (solid, brittle, poor conductor, melting point 115°C)

Chemical Properties:

Metals:

  • Typically lose electrons in reactions (low electronegativity)
  • Form basic or amphoteric oxides
  • React with acids to produce hydrogen gas
  • Form ionic compounds with non-metals
  • Example: 2Na + Cl₂ → 2NaCl (sodium donates electron to chlorine)

Non-metals:

  • Typically gain or share electrons in reactions (high electronegativity)
  • Form acidic oxides
  • Do not react with acids to produce hydrogen
  • Form covalent compounds with other non-metals
  • Example: H₂ + O₂ → 2H₂O (hydrogen and oxygen share electrons)

2. Explain the trend in reactivity of halogens down Group 17 (VII) of the periodic table. Include chemical equations to illustrate displacement reactions.

The reactivity of halogens decreases as you move down Group 17 (VII) from fluorine to iodine. This trend can be explained by several factors:

Atomic size: As you move down the group, the atomic radius increases as new electron shells are added. This means the nucleus is farther from the valence electrons, resulting in a weaker attraction.

Electronegativity: Decreases down the group, meaning the atoms have less ability to attract electrons.

Electron affinity: Generally decreases down the group, indicating less energy is released when an electron is added.

This trend in reactivity is demonstrated through displacement reactions, where a more reactive halogen can displace a less reactive halogen from its salt solution:

Cl₂ + 2KBr → 2KCl + Br₂

Br₂ + 2KI → 2KBr + I₂

However, a less reactive halogen cannot displace a more reactive one:

I₂ + 2KBr → No reaction

This confirms the reactivity order: F₂ > Cl₂ > Br₂ > I₂

The reaction rates decrease down the group, and the stability of the halide ions (X⁻) increases down the group (F⁻ is least stable, I⁻ is most stable), which also contributes to the decreasing reactivity.

3. Describe the industrial production of sulfuric acid using the Contact process, including conditions, reactions, and safety considerations.

The Contact process is used for the industrial production of sulfuric acid (H₂SO₄). The process involves several stages:

Step 1: Production of Sulfur Dioxide

Sulfur is burned in air to produce sulfur dioxide:

S + O₂ → SO₂

Alternatively, hydrogen sulfide from natural gas or metal sulfides can be used:

2H₂S + 3O₂ → 2SO₂ + 2H₂O

4FeS₂ + 11O₂ → 2Fe₂O₃ + 8SO₂

Step 2: Conversion of Sulfur Dioxide to Sulfur Trioxide

SO₂ is oxidized to SO₃ using atmospheric oxygen:

2SO₂ + O₂ ⇌ 2SO₃

Conditions:

  • Temperature: 400-450°C (compromise temperature)
  • Pressure: 1-2 atmospheres
  • Catalyst: Vanadium(V) oxide (V₂O₅)

This is a reversible exothermic reaction. The conditions represent a compromise: higher temperatures increase reaction rate but lower yield, while lower temperatures increase yield but decrease rate.

Step 3: Conversion of Sulfur Trioxide to Sulfuric Acid

SO₃ is not directly added to water as this produces a dangerous mist of H₂SO₄. Instead, it is first dissolved in concentrated H₂SO₄ to form oleum (H₂S₂O₇):

SO₃ + H₂SO₄ → H₂S₂O₇

Oleum is then diluted with water to produce concentrated sulfuric acid:

H₂S₂O₇ + H₂O → 2H₂SO₄

Safety Considerations:

  • Sulfur dioxide and sulfur trioxide are toxic gases
  • Sulfuric acid is highly corrosive
  • Heat management is crucial due to exothermic reactions
  • Corrosion-resistant materials must be used
  • Emission controls are necessary to prevent air pollution
  • Safety protocols for handling concentrated acids

Economic and Environmental Factors:

  • Sulfuric acid is one of the most widely produced chemicals globally
  • Modern plants incorporate recycling of unreacted gases
  • Emissions are scrubbed to remove pollutants
  • Energy recovery systems are used to harness heat from exothermic reactions