Electron Configurations printable pdf download

Electron Configurations

8.2 Electron Configurations

• Building-up (aufbau) principle – as new

electrons are added to the atom, they are

placed in the lowest energy available orbital

• Closed shell configuration represents a

(minimization of the total energy of the atom)

completely filled principal shell (He → 1s

)

– Electron configuration – a list of the occupied

subshells and the number of electrons on them

– Orbital diagrams – each orbital is represented

by a box; the electrons are shown as up or down

arrows depending on the spin quantum number

(+1/2 or -1/2)

• Degenerate orbitals – orbitals with equal energies

– All orbitals in a subshell are degenerate (same n

and l) → the three 2p-orbitals are degenerate

• Hund’s rule – in filling degenerate orbitals,

electrons enter the empty orbitals having identical

spins before pairing in one of them (minimization of

the repulsion between the electrons)

• Outer electrons – electrons in the outermost

occupied principal shell

• Inner (core) electrons – inner shells

• Condensed e

configurations – inner shells

(or part of them) can be abbreviated with the

symbol of the previous noble gas in brackets

→ abbreviated as [He]

Electron Configurations