FYUG Even Semester Exam, 2025
CHEMISTRY: Fundamentals of Chemistry
Instructions: The figures in the margin indicate full marks for the questions.
UNIT-I
1. (a) Mention two important postulates of Bohr's theory. 2
- Electrons revolve around the nucleus in specific circular paths called orbits or stationary states with fixed energy.
- An electron can move from a lower energy level to a higher energy level by absorbing a definite amount of energy, and vice versa by emitting energy.
1. (b) What is meant by dual nature of particles in motion? 2
According to de Broglie, every moving particle (like an electron) behaves both as a particle and as a wave.
This is known as the wave-particle duality, expressed by the equation: wavelength = h / mv.1. (c) Draw the radial probability distribution curves for 1s and 2s electrons. 2
For 1s, the curve shows a single peak.
For 2s, there is one node and two peaks, with the larger peak further from the nucleus.2. (a) (i) State and explain Heisenberg uncertainty principle. Mention its significance. 3
It is impossible to determine simultaneously and precisely both the position and the momentum (or velocity) of a microscopic particle like an electron.
Mathematical expression: (Δx)(Δp) ≥ h / 4π. Its significance lies in the fact that it rules out the existence of definite paths or trajectories for electrons and other similar particles.2. (a) (ii) Numerical: de Broglie wavelength of an electron moving with speed of light. 2
Given: h = 6.62 x 10^-34 J.s, mass (m) = 9.1 x 10^-31 kg, velocity (v) = 3 x 10^8 m/s
Formula: wavelength = h / mv
Calculation: wavelength = (6.62 x 10^-34) / (9.1 x 10^-31 x 3 x 10^8)
Final Answer: 2.42 x 10^-12 meters.
2. (a) (iii) Time-independent Schrödinger wave equation. 3
The equation is: (δ²ψ/δx²) + (δ²ψ/δy²) + (δ²ψ/δz²) + (8π²m/h²)(E - V)ψ = 0
- ψ (psi): Wave function
- m: Mass of the particle
- E: Total energy
- V: Potential energy
- h: Planck's constant
2. (b) (i) State and explain Aufbau principle with example. 3
In the ground state of an atom, orbitals are filled in order of their increasing energies.
Orbitals with lower (n + l) value are filled first.Example: 4s (4+0=4) is filled before 3d (3+2=5) because 4 < 5.
UNIT-II
3. (a) Draw the structures of BF3 and NH3. 2
BF3: Trigonal planar geometry with sp2 hybridization.
NH3: Pyramidal geometry due to one lone pair and sp3 hybridization.
3. (c) Draw resonance structures of isoelectronic NO2- and O3. 2
Both species have bent structures with delocalized pi electrons.
4. (a) (i) Discuss geometry of XeF4 and ClF3 using VSEPR theory. 4
- XeF4: Xenon has 8 valence electrons. 4 bond pairs + 2 lone pairs = 6 electron pairs (Octahedral arrangement). Geometry is Square Planar.
- ClF3: Chlorine has 7 valence electrons. 3 bond pairs + 2 lone pairs = 5 electron pairs (Trigonal bipyramidal arrangement). Geometry is T-shaped.
4. (a) (ii) Draw the MO diagram of N2 molecule. 4
Nitrogen (Z=7) has 14 electrons. Configuration: σ1s² σ*1s² σ2s² σ*2s² (π2px² = π2py²) σ2pz².
Magnetic Property: Since all electrons are paired, N2 is diamagnetic.
UNIT-III
5. (a) Two postulates of Kinetic Theory of Gases. 2
- Gases consist of large numbers of tiny particles (atoms or molecules) which are in constant random motion.
- The actual volume of the gas molecules is negligible compared to the total volume occupied by the gas.
5. (b) Calculate most probable velocity of oxygen at 27°C. 2
Formula: v = sqrt(2RT / M)
T = 27 + 273 = 300 K; R = 8.314 J/mol.K; M = 32 x 10^-3 kg/mol
v = sqrt(2 * 8.314 * 300 / 0.032) = 394.8 m/s.
6. (a) (iii) Difference between Real Gas and Ideal Gas. 2
| Ideal Gas | Real Gas |
|---|---|
| Obeys gas laws at all T and P. | Obeys gas laws only at low P and high T. |
| No intermolecular forces. | Intermolecular forces are present. |
UNIT-IV
7. (a) What is viscosity? Variation with temperature. 2
Viscosity is the internal resistance to flow in a liquid.
As temperature increases, kinetic energy increases, weakening intermolecular forces, so viscosity decreases.8. (a) (iii) Explain Schottky and Frenkel defects. 3
- Schottky Defect: Equal number of cations and anions are missing from their lattice sites. Decreases density.
- Frenkel Defect: An ion (usually cation) leaves its site and occupies an interstitial position. Density remains constant.
UNIT-V
9. (a) Conditions for Homolytic and Heterolytic cleavage. 2
- Homolytic: Occurs in non-polar bonds, usually in the presence of UV light or high temperature. Forms free radicals.
- Heterolytic: Occurs in polar bonds or in the presence of polar solvents. Forms carbocations and carbanions.
10. (a) (i) What is Hyperconjugation? Stability of carbocations. 3
Hyperconjugation is the delocalization of sigma electrons of a C-H bond into an adjacent empty p-orbital or pi-system.
More the number of alpha-hydrogens, more the hyperconjugative structures, and higher the stability.Order of stability: (CH3)3C+ (Tertiary) > (CH3)2CH+ (Secondary) > CH3CH2+ (Primary) > CH3+ (Methyl).