Electron Configuration and Basic Quantum Model NC Essential Standard 1.3.2 Quantum mechanics and it relation to electron configuration.

Electron Configuration and Basic Quantum Model

NC Essential Standard1.3.2

Quantum mechanics and it relation to electron configuration

Quantum Model• The quantum model describes the probability of locating an

electron at any place.• Heisenberg Uncertainty Principle – it is impossible to know both

the velocity (momentum) and the position of an electron at the same time.– The impact of a photon of light alters the motion of the electron

in unpredictable ways, so measuring position changes velocity• Each electron is assigned four quantum numbers that describe it.

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

Principle Energy Level, n• Indicates main energy level occupied by e-• Always a whole number (1, 2, …)• To calculated the number of electrons that a given energy level can

have. Simpley use the formula 2n2

• 1st level can hold 2(1)2 = 2 e-• 2nd level can hold 2(2)2 = 8 e-• 3rd level can hold 2(3)2 = 18 e-• 4th level can hold 2(4)2 = 32 e-• The period indicates the # of principle energy levels

Sublevels, l• Main energy levels are then divided into sublevels• Indicates the shape or type of orbital

– s, p, d, f – s sublevel is spherical and holds 2 e-– p sublevel is shaped like a dumbbell and holds 6 e-– d holds 10 e-– f holds 14 e-

Orbitals, m• Represents the orbital within the sublevel where the electron is

located• Each orbital holds a pair of electrons therefore:

– 1 s orbital– 3 p orbitals– 5 d orbitals– 7 f orbitals

Spin, s• Each orbital holds 2 electrons that will always spin in opposite

directions the electrons are represented by +1/2 and -1/2. Note arrows are used in the orbital notation for example ↑↓.

• The s orbital is spherically shaped. There is one s orbital for each value n = 1,2,3,…, of the principle number.

P Orbitals

• For each of the values n = 3, 4, 5,…, there are five d orbitals. Four of the five have similar shapes, but differ in orientation.

Electron Configurations

• Shows the electron arrangement in an atom, always represents the lowest possible energies

• Aufbau Principle (German for “building up”) – electrons fill orbitals that have the lowest energies first

Explanation of configuration

1s2Energy levelEnergy level

subl

evel

subl

evel

Number of electronsNumber of electrons

Practice Write electron configurations

– Pb: • 1s22s22p63s23p6

Note All the superscripts should add up to the number of electrons

Electron Configurations• H: 1s1

• Be: 1s2

• Li: 1s2 2s1

• Be: 1s2 2s2

• B:1s2 2s2 2p1

• Cl: 1s2 2s2 2p6 3s2 3p5

• We just need to account for all the electrons and their locations

• Since they fill up the lower levels first, only the last shell (Valence) varies from the previous element’s configuration

Notice 3s2 and 3p5 add together to produce the valence (outer most electrons) electrons in the atom. This atom has7 valence electrons.

Practice• Write the electron configuration for• C• N• O• F• Ne• Na• Mg• Al

Practice• Write the electron configuration for• C: 1s2 2s2 2p2

• N: 1s2 2s2 2p3

• O: 1s2 2s2 2p4

• F: 1s2 2s2 2p5

• Ne: 1s2 2s2 2p6

• Na: 1s2 2s2 2p6 3s1

• Mg: 1s2 2s2 2p6 3s2

• Al: 1s2 2s2 2p6 3s2 3p1

Refer to this Periodic Table when writing electron configurations

The numbers in

front of the “s” and

“p” are the same as the row #

1A are s 1 and 2A are s 2

Shorthand Notation• Shorthand notation uses the noble gases as a

reference point, for example

– Na:

»[Ne]3s2

Noble GasHighest energy level / period

Sublevel / block

Number of valence electrons / group number

Shorthand Notation Samples

Li [He] 2s1

He 1s2

K [Ar] 4s1

P [Ne] 3s2 3p3

Cl [Ne] 3s2 3p5

Al [Ne] 3s2 3p1

Shorthand Notation Practice

B

Ar

K

Ca

H

Mg

Shorthand Notation Practice Answers

B [He] 2s2

Ar [Ne] 3s2 3p6

K [Ar] 4s1

Ca [Ar] 4s2

H 1s1

Mg [Ne] 3s2

Orbital notation

• Orbital notation uses lines to represent orbits and arrows to represent the spin of each electron.

1s

Energy level and sublevel

Electron spinning clockwise

Electron spinning counter clockwise

Orbital Notation• Orbital notation uses lines to represent orbits

and arrows to represent the spin of each electron.

• oxygen has a total of 8 e-The e- configuration for O:

1s2 2s2 2p4

Hund’s Rule: e- spread out within equivalent orbitals

↑↓ ↑↓ ↑↓ ↑ ↑1s 2s 3s 3s 3p

Sample Orbital Notation

He

Be

N

F

Practice Orbital Notation Practice

Element Orbital Notation

Li

C

Al

O

Element Orbital Notation

Li

C

Al

O

1s2 2s1

1s2 2s2 3s2 3p13p1

1s2 2s2 2p2 2p2 2p2 3s2 3p1

1s2 2s2 2p2 2p2 2p2

Symbol Group# Valence e-

Period S,p,d,f block

Highest energy level

[Ar]4s2

[Ne]3s23p3

[He]2s22p5

1s22s2

1s22s22p3

1s22s22p63s23p1

Mixed practice

Symbol Group# Valence e-

Period S,p,d,f block

Highest energy level

[Ar]4s2 Ca 2 2 4 s 4

[Ne]3s23p3 P 5A /15 5 3 p 3

[He]2s22p5 O 6A /16 7 2 p 4

1s22s2 Be 2 2 2 s 2

1s22s22p3 N 5A /15 5 2 p 2

1s22s22p63s23p1 Al 3A /13 3 3 p 3