Atomic orbitals, electronic configurations and the periodic table

Atomic spectra explanation

Discrete lines in atomic spectra are explained by electrons displaying both particle and wave properties

Standing wave behaviour

Electrons behave as standing (stationary) waves that vibrate in time but do not move in space

Orbitals

Different sizes and shapes of standing waves around the nucleus that can hold up to two electrons

Orbital types

Identified as s

Electron energy levels

Electrons have fixed amounts of energy called quanta

Quantum numbers

Any electron in an atom can be described using four quantum numbers

Principal quantum number (n)

Indicates the main energy level and relates to orbital size

Angular momentum quantum number (l)

Determines the shape of the subshell and has values from 0 to n−1

Magnetic quantum number (ml)

Determines the orientation of the orbital and has values between −l and +l

Spin magnetic quantum number (ms)

Determines the direction of electron spin with values of +½ or −½

Aufbau principle

Electrons fill orbitals in order of increasing energy

Hund’s rule

Electrons fill degenerate orbitals singly with parallel spins before pairing

Pauli exclusion principle

No two electrons in an atom can have the same set of four quantum numbers

Degenerate orbitals

Orbitals within each subshell of an isolated atom have the same energy

Orbital box notation

Used to represent relative orbital energies diagrammatically for first four shells

Electronic configurations

Can be written using spectroscopic notation and orbital box notation for elements 1–36

Periodic table blocks

Subdivided into s

Ionisation energy trends

Variation in first

Ionisation anomalies

Explained by considering full and half-filled subshell stability

Subshell stability

Special stability associated with half-filled and full subshells results in higher ionisation energies

VSEPR theory

Used to predict shapes of molecules and polyatomic ions based on electron pair repulsions

Finding electron pairs

Add valence electrons on central atom

Electron pair repulsion

Electron pairs are negatively charged and arrange to minimise repulsion and maximise separation

Linear arrangement

Occurs with two electron pairs

Trigonal planar arrangement

Occurs with three electron pairs

Tetrahedral arrangement

Occurs with four electron pairs

Trigonal bipyramidal arrangement

Occurs with five electron pairs

Octahedral arrangement

Occurs with six electron pairs

Molecular shape

Determined by shape adopted by atoms based on electron pair arrangement

Electron dot diagrams

Can be used to show arrangements of atoms and electron pairs

Repulsion strength order

Non-bonding/non-bonding > non-bonding/bonding > bonding/bonding