Atomic Structure — A/L Chemistry

What must I remember about Atomic Structure?

• Atoms consist of a dense positive nucleus (protons + neutrons) surrounded by quantized electrons in orbitals (s, p, d, f).
• Quantum numbers describe electron states: principal n, orbital angular momentum l (0 to n-1), magnetic ml (-l to +l), and spin ms (+1/2, -1/2).
• Electronic configuration follows Aufbau principle (lowest energy first), Pauli exclusion principle (opposite spins in an orbital), and Hund's rule (parallel spins in degenerate orbitals).
• Successive ionization energies show sharp jumps when electrons are removed from a new inner principal quantum shell, identifying the periodic group.
• Hydrogen line emission spectra result from electron transitions between discrete energy levels: Lyman series (UV, n=1), Balmer series (Visible, n=2), Paschen series (IR, n=3).

Test yourself (1 minute)

1. Anomalous configurations

   Cr is [Ar] 3d⁵ 4s¹ and Cu is [Ar] 3d¹⁰ 4s¹ due to half-filled and fully-filled 3d orbital stability.

2. Where do the first ionization energy drops fall across Periods 2 and 3, and why?

   Period 2 & 3 first ionization energy drops occur at Group 2 to 13 (s² to s²p¹) and Group 15 to 16 (stable p³ to paired p⁴ repulsion).

3. Photon energy transition relationship

   ΔE = hν = hc/λ.

Practise Atomic Structure questions today

Source: NIE G.C.E. (A/L) Chemistry Syllabus (Unit 1)

What comes next?

Next in the syllabus

Where does Atomic Structure fit in the syllabus?

Grade 12 · Term 1