Electron Configuration

Notes

• Ground State –

The lowest energy state of an atom.

• Excited State –

State in which an atom has a higher potential energy then it has in its ground state.

• Heisenberg Uncertainty Principle –

It is impossible to determine simultaneously both the position and velocity of an electron or any other particle. (Can’t exactly predict where electrons will be, just give a general idea.)

• Orbital –

Three dimensional region around the nucleus that indicates the probable location of an electron.

• Quantum Numbers –

Numbers that specify the properties of atomic orbital’s and the properties of electrons in orbital’s.

• Principle Quantum Number –

(n) The main energy level occupied by the electron.– Positive numbers only 1, 2, 3, etc

• Angular Momentum Quantum Number –

(l) The shape of the orbital.– Starts at 0 and then positive integers till n – 1

is reached• Ex. If n = 2, then l = 0, 1• Ex. If n = 4, then l = 0, 1, 2, 3

Orbital Letter Designations

l Letter

0 s

1 p

2 d

3 f

• Magnetic Quantum Numbers –

(m) The orientation of an orbital around the nucleus.– Starts at –l and it each integer to l

• Ex. If l = 2, then m = -2, -1, 0, 1, 2

• Ex. If l = 3, then m = -3, -2, -1, 0 , 1, 2, 3

• Ex. If n = 5, then l = 0, 1, 2, 3, 4,

then m = -4, -3, -2, -1, 0, 1, 2, 3, 4

• Spin Quantum Number –

Indicate the two fundamental spin states of an electron in an orbital.

– Can only be + ½ or – ½

Quantum Number Relationships in Atomic Structure

PrincipleQuantumNumber (Main Energy Level)

SublevelsIn Main Energy Level

Number of Orbital’s per

Sublevel

Number of Orbital’s per Main Energy

Level

Number of Electrons

per Sublevel

Number of Electrons per Main Energy Level

1 s 1 1 2 2

2s 1

42

8p 3 6

3

s 1

9

2

18p 3 6

d 5 10

4

s 1

16

2

32p 3 6

d 5 10

f 7 14

• Electron Configuration – The arrangement of electron’s in an atom.

• Aufbau Principle – An electron occupies the lowest energy orbital that can receive it.

• Pauli Exclusion Principle – No two electrons in the same atom can have the same set of four quantum numbers.

• Hunds Rule – Orbital’s of equal energy are each occupied by one electron before any orbital is occupied by a second electron.

1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p6 7s2 5f14 6d10

Orbital Sample 1

• The electron configuration of boron is 1s22s22p1. How many electrons are present in an atom of boron? What is the atomic number of boron? Write the orbital notation for boron.

Number of electrons =

super scripts added together

• Number of electrons = 2 + 2 + 1

• Number of electrons = 5

Atomic Number = look on PT

• Atomic Number = 5

Orbital Notation = ___ ___ ___ ___ ___ 1s 2s 2px 2py 2pz

• Start with the first orbital…

___ ___ ___ ___ ___ 1s 2s 2px 2py 2pz

• Move onto the next orbital…

___ ___ ___ ___ ___ 1s 2s 2px 2py 2pz

• According to Hunds rule, we have to fill each orbital of the 2p level with one electron first, then go back and fill with the second electron…

___ ___ ___ ___ ___ 1s 2s 2px 2py 2pz

Orbital Sample 2

The electron configuration of nitrogen is 1s22s22p3. How many electrons are present in a nitrogen atom? What is the atomic number of nitrogen? Write the orbital notation for nitrogen.

Number of electrons =

super scripts added together

• Number of electrons = 2 + 2 + 3

• Number of electrons = 7

Atomic Number = look on PT

• Atomic Number = 7

Orbital Notation = ___ ___ ___ ___ ___ 1s 2s 2px 2py 2pz

• Start with the first orbital…

___ ___ ___ ___ ___ 1s 2s 2px 2py 2pz

• Move onto the next orbital…

___ ___ ___ ___ ___ 1s 2s 2px 2py 2pz

• According to Hunds rule, we have to fill each orbital of the 2p level with one electron first, then go back and fill with the second electron…

___ ___ ___ ___ ___ 1s 2s 2px 2py 2pz

Orbital Sample 3

The electron configuration of fluorine is 1s22s22p5. What is the atomic number of fluorine? How many of its p orbital’s are filled? How many unpaired electrons does a fluorine atom contain?

Atomic Number = look on PT• Atomic Number = 9

How many of its p orbital’ are filled = ___ ___ ___ ___ ___1s 2s 2px 2py 2pz

How many of its p orbital’s are filled = 2

How many unpaired electrons does a fluorine atom contain = 1

• Octet of Electrons –

When the s and p orbital’s are filled.

Octet = 8

s orbital = 2 + p orbital = 6

2 + 6 = 8

• Nobel Gas –

The group 18 elements. No unpaired electrons and all orbital’s of the energy level are full.

E- Config. Sample 1

Write both the complete electron-configuration notation and the noble-gas notation for iron, Fe.

Write the complete electron-configuration notation…

• Figure out number of electronsIn a stable atom, number of protons =

number of electrons

Fe = 26

• Start writing electron configuration till number of electrons is reached

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

Write the noble-gas notation…

• Find the highest filled p orbital and its Noble gas

3p6 = Ar

• Write the noble gas in brackets and then the remainder of the full electron configuration

[Ar] 4s23d6

E- Config. Sample 2

Write both the complete electron configuration notation and the noble-gas notation for iodine, I.

Write the complete electron-configuration notation…

• Figure out number of electronsIn a stable atom, number of protons =

number of electrons

I = 53

• Start writing electron configuration till number of electrons is reached

1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p5

Write the noble-gas notation…

• Find the highest filled p orbital and its Noble gas

4p6 = Kr

• Write the noble gas in brackets and then the remainder of the full electron configuration

[Kr] 5s24d105p5

E- Config. Sample 3

Without consulting the periodic table or a table in this chapter, write the complete electron configuration for the element with atomic number 25.

Write the complete electron-configuration notation…

• Figure out number of electronsGiven 25

• Start writing electron configuration till number of electrons is reached

1s2 2s2 2p6 3s2 3p6 4s2 3d5