Atomic Structure & Periodic Trends

Subatomic particles:

Proton — positive charge, in nucleus, determines element identity (atomic number)

Neutron — no charge, in nucleus, determines isotope

Electron — negative charge, in electron cloud

Quantum numbers:

n — principal quantum number (energy level, shell)

l — angular momentum (subshell: 0=s, 1=p, 2=d, 3=f)

ml — magnetic quantum number (orbital orientation)

ms — spin quantum number (+½ or −½)

Electron configuration:

Aufbau principle: fill lowest energy orbitals first

Hund's rule: one electron per orbital before pairing

Pauli exclusion: no two electrons have same four quantum numbers

Periodic trends:

Atomic radius: Increases down group, decreases across period (left to right)

Ionization energy: Decreases down group, increases left to right

Electronegativity: Decreases down group, increases left to right (F is highest)

Electron affinity: Generally increases left to right

Reference:

Wikipedia: Atomic Structure

https://en.wikipedia.org/wiki/Atomic_structure