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CC04 — Chemical Bonding & States of Matter

📖 CC04  ·  CDS General Science — Chemistry ★ High Priority

Chemical bonds hold atoms together; without them, no molecule would exist. States of matter describe how molecules are arranged. CDS tests bond types (ionic vs covalent), hydrogen bonding (why water has such unusual properties), and gas laws directly.

📌 CDS Focus: Ionic bond = metal + non-metal (electron transfer); Covalent bond = non-metal + non-metal (electron sharing); Hydrogen bonding (explains high boiling point of water); Boyle's Law (P∝1/V); Charles's Law (V∝T). Properties of ionic compounds vs covalent compounds is a direct CDS comparison question.

1. Types of Chemical Bonds

Fig. 1 — Three Types of Chemical Bonds: Formation, Properties and Examples
CHEMICAL BONDS — Formation, Properties, Examples IONIC BOND Electron Transfer Formation: Metal GIVES electron to non-metal. Between: Metal + Non-metal Examples: NaCl, MgO, CaF₂ KCl, Na₂O, AlCl₃ Properties: High melting point Soluble in water Conduct electricity when melted or dissolved COVALENT BOND Electron Sharing Formation: Atoms SHARE pairs of electrons. Between: Non-metal + Non-metal Examples: H₂, O₂, N₂, Cl₂ H₂O, CH₄, CO₂, HCl Properties: Low melting point Poor conductors (usually) Exist as gases/liquids at room temp METALLIC BOND Sea of Electrons Formation: Metal ions in lattice; free electrons form a sea/cloud. Between: Metal atoms only Examples: Fe, Cu, Al, Na, Au Properties: Good conductors (heat & electricity) Lustrous, ductile, malleable Generally high melting points

2. Hydrogen Bonding

What is Hydrogen Bonding?

A hydrogen bond forms when a hydrogen atom covalently bonded to a highly electronegative atom (F, O, or N) is attracted to another electronegative atom nearby.

Condition: H must be bonded to F, O, or N only (the three most electronegative elements)
Strongest: H—F > H—O > H—N

Effects of hydrogen bonding:
● Unusually high boiling point of water (100°C) vs H₂S (−60°C) — even though H₂S has higher mass
● High surface tension of water
● DNA double helix held together by hydrogen bonds (A-T and G-C base pairs)
● Protein secondary structure (alpha helix, beta sheet)

3. States of Matter & Gas Laws

Fig. 2 — States of Matter: Particle Arrangement and Key Gas Laws
STATES OF MATTER & GAS LAWS SOLID Closely packed Fixed shape & volume. Particles vibrate in place. LIQUID Fixed volume; takes shape of container. GAS No fixed shape/volume. Fills any container. GAS LAWS (for Ideal Gases) Boyle's Law: P ∝ 1/V (const T) → P₁V₁ = P₂V₂ If pressure doubles, volume halves. Charles's Law: V ∝ T (const P) → V₁/T₁ = V₂/T₂ T must be in Kelvin. V doubles if T doubles. Ideal Gas Equation: PV = nRT n=moles; R=8.314 J/mol·K

📝 CDS PYQs — Chemical Bonding

Q1. NaCl is an example of: CDS PYQ
(a) Covalent compound(b) Ionic compound(c) Metallic compound(d) Coordinate compound
✔ Answer: (b) Ionic compound
NaCl (sodium chloride/common salt) is an ionic compound. Sodium (metal, Group 1) gives one electron to chlorine (non-metal, Group 17), forming Na⁺ and Cl⁻ ions held together by electrostatic attraction. Ionic compounds have high melting points, dissolve in water, and conduct electricity in solution or molten state.
Q2. Water has an unusually high boiling point compared to H₂S because of: CDS PYQ
(a) Covalent bonding(b) Ionic bonding(c) Hydrogen bonding(d) Van der Waals forces
✔ Answer: (c) Hydrogen bonding
Water (H₂O) has a boiling point of 100°C while H₂S (which is heavier) boils at −60°C. This anomaly is explained by hydrogen bonding — oxygen is highly electronegative, and H₂O molecules form hydrogen bonds with each other, requiring extra energy to break. H₂S cannot form hydrogen bonds as sulfur's electronegativity is insufficient.
Q3. A gas is compressed from 4 L to 2 L at constant temperature. If initial pressure was 1 atm, new pressure is: CDS PYQ
(a) 0.5 atm(b) 1 atm(c) 2 atm(d) 4 atm
✔ Answer: (c) 2 atm
By Boyle's Law: P₁V₁ = P₂V₂ (constant temperature). 1 × 4 = P₂ × 2. P₂ = 4/2 = 2 atm. Pressure and volume are inversely proportional at constant temperature. When volume is halved, pressure doubles.

🧠 Quick Memory Chart — CC04

⚛ Bond Types
  • Ionic: metal + non-metal (e⁻ transfer)
  • Covalent: non-metal + non-metal (sharing)
  • Metallic: metal + metal (e⁻ sea)
  • Ionic: high MP, conducts when melted
  • Covalent: low MP, poor conductors
💧 H-bonding
  • Only with F, O, N
  • Strongest: H—F bond
  • Water: high BP due to H-bonding
  • DNA held by H-bonds
  • Explains many anomalous properties
☁ Gas Laws
  • Boyle: P∝1/V (const T): P₁V₁=P₂V₂
  • Charles: V∝T (const P): V₁/T₁=V₂/T₂
  • Always use T in Kelvin (K = °C + 273)
  • PV = nRT (ideal gas)
  • STP: 1 mol gas = 22.4 L

📝 Practice Exercise

E1. H₂O is an example of:
(a) Ionic compound(b) Covalent compound(c) Metallic compound(d) Coordinate compound
E2. DNA double helix is held together by:
(a) Covalent bonds(b) Ionic bonds(c) Hydrogen bonds(d) Metallic bonds
E3. At constant pressure, volume of a gas is doubled. The temperature:
(a) Halves(b) Doubles (in Kelvin)(c) Stays same(d) Becomes four times
Answers: E1 → (b) Covalent [O and H are both non-metals]  |  E2 → (c) Hydrogen bonds (between A-T and G-C base pairs)  |  E3 → (b) Doubles (Charles's Law: V/T = constant, so T must double if V doubles)
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