ELECTRON CONFIGURATION

LABEL THE SUBLEVELS (1S, 2S, …)

PRACTICE 1

Sulfur ( ______ electrons)Electron configuration:

a. How many E.L. in an atom of S have e-?

b. How many e- are in the 2nd energy level?

PRACTICE 1 ANSWER

Sulfur ( __16____ electrons)Electron configuration: 1s2 2s2 2p6 3s2 3p4

a. How many E.L. in an atom of S have e-? Three

b. How many e- are in the 2nd energy level? 8 (2+6 - just add the superscripts)

PRACTICE 2

• Iron (________ electrons)• Electron Configuration:

a. How many E.L. in an atom of Fe contain e-?

b. b. How many e- in 3rd energy level?

PRACTICE 2 ANSWER

• Iron (___26_____ electrons)• Electron Configuration:

1s2 2s2 2p6 3s2 3p6 4s2 3d6

a. How many E.L. in an atom of Fe contain e-? Four

b. How many e- in 3rd energy level? 14 (2+6+6)

NOBLE GAS NOTATION (“SHORT HAND”)

• This is used to represent electron configurations of noble gases using bracketed symbols.

SHORT HAND PRACTICE

• Use shortcut method to write e-configurations for Ar and P.

• Ar:

• P:

[Ne] 3s2 3p6 or [Ar]

[Ne] 3s2 3p3

GROUND STATE VS EXCITED STATE

Ground State – The most stable, lower energy arrangement of the electrons in an atom. (The electrons are in the correct order of orbitals.)

 Excited State – When atom gains energy the electrons jump into higher energy level. Example: Identify the following atoms and describe their state. (Ground or Excited)

a. 1s22s22p63s23p64s13d104p3

b. 1s22s22p63s23p64s23d104p5

c. 1s22s22p63s23p64s23d104p65s24d8

ELECTRON CONFIGURATION

A. Aufbau Principle – Electrons enter orbitals of lower energy first.1s2, 2s2, 2p6, 3s2, 3p6, 4s2, 3d10, 4p6, 5s2, 4d10, 5p6, 6s2, 4f14, 5d10, 6p6, 7s2, 5f14, 6d10, 7p6 (or use PT) B. Pauli Exclusion Principle – No more than __2______ electrons can occupy

the same orbital AND they must spin in opposite directions. (Opposite spins help hold e- in an orbital by creating magnetic attraction.)

C. Hund’s Rule – Orbitals of equal energy must EACH have _1____ electron

with the same ____spin______ before any orbital is occupied by a 2nd electron.

ELECTRON CONFIGURATION