Introduction
The structure of atom is one of the most important topics in chemistry. It explains how atoms are built and how electrons behave inside them. This chapter forms the base for understanding chemical bonding and periodic properties.
An atom consists of three fundamental particles: electron, proton, and neutron.
Discovery of Subatomic Particles
Electron (J.J. Thomson)
Charge to mass ratio:
e/m = 1.758820 × 10^11 C kg^-1
Proton
Charge of proton:
charge = +1.602 × 10^-19 C
Neutron (Chadwick)
Mass of neutron ≈ mass of proton
Atomic Models
Thomson Model
Atom is a positively charged sphere with electrons embedded in it.
Rutherford Model
Force between nucleus and electron:
F = (1 / (4π ε0)) × (Z e^2 / r^2)
Bohr Model
Energy of electron in nth orbit:
En = -2.18 × 10^-18 / n^2 J
Radius of nth orbit:
rn = (n^2 h^2) / (4 π^2 m e^2)
Velocity of electron:
vn = (Z e^2) / (2 ε0 h n)
Dual Nature of Matter
De Broglie equation:
λ = h / (m v)
Heisenberg Uncertainty Principle
Δx × Δp ≥ h / (4π)
Quantum Mechanical Model
Schrödinger equation:
H ψ = E ψ
Quantum Numbers
Principal quantum number:
n = 1, 2, 3…
Azimuthal quantum number:
l = 0 to (n − 1)
Magnetic quantum number:
ml = −l to +l
Spin quantum number:
ms = +1/2 or −1/2
Electronic Configuration
Aufbau principle:
Energy ∝ (n + l)
Pauli exclusion principle:
No two electrons have same set of quantum numbers (n, l, ml, ms)
Hund’s rule:
Maximum multiplicity (electrons fill singly first)
Important Equations
Planck equation:
E = hν
Frequency relation:
ν = c / λ
Rydberg equation:
1/λ = R (1/n1^2 − 1/n2^2)
Conclusion
The structure of atom explains how electrons are arranged and how they behave. These concepts are essential for understanding all chemical reactions and properties.