NCERT Solutions for Class 11 Chemistry Chapter 2 Structure of Atom

Short Note:

• Electron (discovered by J.J. Thomson, via cathode ray experiments): negatively charged, e/m = 1.75 × 10&sup8; C/g.

• Proton (discovered by Goldstein, via anode/canal rays): positively charged particle present in the nucleus.

• Neutron (discovered by Chadwick): neutral particle present in the nucleus, mass nearly equal to that of a proton.

Short Note:

• Rutherford's Nuclear Model: based on the alpha-particle scattering experiment, proposed that most of the atom's mass and all positive charge is concentrated in a tiny, dense nucleus, with electrons revolving around it.

• Bohr's Model: electrons revolve in fixed circular orbits (energy levels) without radiating energy; energy is absorbed or emitted only when an electron jumps between orbits, explaining the hydrogen line spectrum.

Short Note:

• de Broglie's Equation: λ = h/mv, showing that matter (like light) has both wave and particle nature.

• Heisenberg's Uncertainty Principle: it is impossible to determine simultaneously, with absolute accuracy, both the position and momentum of a microscopic particle like an electron.

• The Quantum Mechanical Model describes electrons in terms of orbitals (regions of maximum probability of finding an electron), characterised by four quantum numbers: principal (n), azimuthal (l), magnetic (m_l), and spin (m_s).

Short Note:

• Aufbau Principle: electrons are filled into orbitals in order of increasing energy.

• Pauli Exclusion Principle: no two electrons in an atom can have the same set of all four quantum numbers.

• Hund's Rule of Maximum Multiplicity: electrons are distributed singly among orbitals of the same subshell before pairing up.