Quantum Numbers

Describes the arrangement of electrons in atoms in terms of:energy levels, sizePathway of travelDirection of rotation

Principal Quantum number (n)

Contain electrons that are similar in

energy and distance from nucleus

Low energy electrons are closest to the

nucleus

Identify by numbers 1, 2, 3, 4, 5, 6…..

The first shell (1) is lowest in energy, 2nd

level next and so on 1<2<3<4

Number of Electrons

Maximum number of electrons in any electron energy level = 2n2

n =1 2(1)2 = 2

n =2 2(2)2 = 8

n =3 2(3)2 = 18

Orbital Quantum number

Indicates the pathway of travel

Electrons move in different paths

due to their negative charge.

Designated s, p, d, f ..

Sublevel energy: s<p<d<f

Magnetic Quantum number

Orientation of path Direction of movement with respect

to the nucleus

1 s orbital for every energy level

Spherical shaped

Each s orbital can hold 2 electrons Called the 1s 2s 3s etc..

orbitals.

S orbitals

P orbitals

3 different directions3 identical shapesEach can hold 2 electrons

P Orbitals put together

D orbitals Higher in energy than s or p due to

advanced shape 5 shapes, 4 are identical

F orbitals

More complex still

Have seven different shapes

F orbitals More complex still

Spin Quantum number Describes rotation of electron in an

orbital Either clockwise (+1/2) or Counter clockwise (-1/2)

Summary Seven energy levels (n=1,2,3,4…) Four pathways (s,p,d,f) Orientations: s=1, p=3, d=5, f=7 Two spins in each orbital Maximum electrons are: s=2, p=6,

d=10, f=14

Summary

s

p

d

f

# of shapes/orbitals

Max # electrons/orbital

Starts at energy level

1 2 1

3 6 2

5 10 3

7 14 4

By Energy Level First Energy Level only s orbital only 2 electrons 1s2

Second Energy Level

s and p orbitals are available

2 in s, 6 in p 2s22p6

8 total electrons

By Energy Level Third energy level s, p, and d

orbitals 2 in s, 6 in p, and

10 in d 3s23p63d10

18 total electrons

Fourth energy level

s,p,d, and f orbitals

2 in s, 6 in p, 10 in d, ahd 14 in f

4s24p64d104f14

32 total electrons

By Energy Level Any more than

the fourth and not all the orbitals will fill up.

You simply run out of electrons

The orbitals do not fill up in a neat order.

The energy levels overlap

Lowest energy fill first.

Electron Locations

Main Energy Levels Sublevels

n=4 4s, 4p, 4d, 4f

n=3 3s, 3p, 3d

n=2 2s, 2p

n=1 1s

Sublevels in n = 1,2, 3

3d

n = 3 3p

3s

2p

n = 2 2s

n = 1 1s

Electrons Allowed

All electrons in the same sublevel have the same energy.

All 2s electrons have the same energy. All 2p electrons, the same energy which is slightly higher than that of the 2s electrons

s sublevel 2 electrons

p sublevel 6 electrons

d sublevel 10 electrons

f sublevel 14 electrons

Incr

easi

ng e

nerg

y

1s

2s

3s

4s

5s6s

7s

2p

3p

4p

5p

6p

3d

4d

5d

7p 6d

4f

5f

Electron Configurations

List of subshells containing electrons

Written in order of increasing energy

Superscripts give the number of electrons

Electron Configuration

Example: Neon

number of electrons

1s2 2s2 2p6

main shell subshell

Electron Configurations The way electrons are arranged in

atoms. Aufbau principle- electrons enter the

lowest energy first. This causes difficulties because of the

overlap of orbitals of different energies. Pauli Exclusion Principle- at most 2

electrons per orbital - different spins

Electron Configuration Hund’s Rule- When electrons occupy

orbitals of equal energy they don’t pair up until they have to .

Let’s determine the electron configuration for Phosporus

Need to account for 15 electrons

The first to electrons go into the 1s orbital

Notice the opposite spins

only 13 more

Incr

easi

ng e

nerg

y

1s

2s

3s

4s

5s6s

7s

2p

3p

4p

5p

6p

3d

4d

5d

7p 6d

4f

5f

The next electrons go into the 2s orbital

only 11 more

Incr

easi

ng e

nerg

y

1s

2s

3s

4s

5s6s

7s

2p

3p

4p

5p

6p

3d

4d

5d

7p 6d

4f

5f

• The next electrons go into the 2p orbital

• only 5 more

Incr

easi

ng e

nerg

y

1s

2s

3s

4s

5s6s

7s

2p

3p

4p

5p

6p

3d

4d

5d

7p 6d

4f

5f

• The next electrons go into the 3s orbital

• only 3 more

Incr

easi

ng e

nerg

y

1s

2s

3s

4s

5s6s

7s

2p

3p

4p

5p

6p

3d

4d

5d

7p 6d

4f

5f

Incr

easi

ng e

nerg

y

1s

2s

3s

4s

5s6s

7s

2p

3p

4p

5p

6p

3d

4d

5d

7p 6d

4f

5f

• The last three electrons go into the 3p orbitals.

• They each go into seperate shapes

• 3 upaired electrons• 1s22s22p63s23p3

The easy way to remember

1s2s 2p3s 3p 3d4s 4p 4d 4f

5s 5p 5d 5f6s 6p 6d 6f7s 7p 7d 7f

• 1s2

• 2 electrons

Fill from the bottom up following the arrows

1s2s 2p3s 3p 3d4s 4p 4d 4f

5s 5p 5d 5f6s 6p 6d 6f7s 7p 7d 7f

• 1s2 2s2

• 4 electrons

Fill from the bottom up following the arrows

1s2s 2p3s 3p 3d4s 4p 4d 4f

5s 5p 5d 5f6s 6p 6d 6f7s 7p 7d 7f

• 1s2 2s2 2p6 3s2

• 12 electrons

Fill from the bottom up following the arrows

1s2s 2p3s 3p 3d4s 4p 4d 4f

5s 5p 5d 5f6s 6p 6d 6f7s 7p 7d 7f

• 1s2 2s2 2p6 3s2

3p6 4s2

• 20 electrons

Fill from the bottom up following the arrows

1s2s 2p3s 3p 3d4s 4p 4d 4f

5s 5p 5d 5f6s 6p 6d 6f7s 7p 7d 7f

• 1s2 2s2 2p6 3s2

3p6 4s2 3d10 4p6

5s2

• 38 electrons

Fill from the bottom up following the arrows

1s2s 2p3s 3p 3d4s 4p 4d 4f

5s 5p 5d 5f6s 6p 6d 6f7s 7p 7d 7f

• 1s2 2s2 2p6 3s2

3p6 4s2 3d10 4p6

5s2 4d10 5p6 6s2

• 56 electrons

Fill from the bottom up following the arrows

1s2s 2p3s 3p 3d4s 4p 4d 4f

5s 5p 5d 5f6s 6p 6d 6f7s 7p 7d 7f

• 1s2 2s2 2p6 3s2

3p6 4s2 3d10 4p6

5s2 4d10 5p6 6s2

4f14 5d10 6p6 7s2

• 88 electrons

Fill from the bottom up following the arrows

1s2s 2p3s 3p 3d4s 4p 4d 4f

5s 5p 5d 5f6s 6p 6d 6f7s 7p 7d 7f

• 1s2 2s2 2p6 3s2

3p6 4s2 3d10 4p6

5s2 4d10 5p6 6s2

4f14 5d10 6p6 7s2

5f14 6d10 7p6 • 108 electrons

Writing Electron Configurations

H 1s1

He 1s2

Li 1s2 2s1

C 1s2 2s2 2p2

S 1s2 2s2 2p6 3s2 3p4

Find element on the periodic tableUse the order of filling indicated

across each period

Groups 1-2 = ns level

Groups 3-8 = np level

Transition = (n-1)d level

Lanthanides = (n-2)f level

Periodic Table and Electron Configuration

Exceptions to Electron Configuration

Orbitals fill in order Lowest energy to higher energy. Adding electrons can change the

energy of the orbital. Half filled orbitals have a lower

energy. Makes them more stable. Changes the filling order

Write these electron configurations

Titanium - 22 electrons 1s22s22p63s23p64s23d2

Vanadium - 23 electrons 1s22s22p63s23p64s23d3

Chromium - 24 electrons 1s22s22p63s23p64s23d4 is expected But this is wrong!!

Chromium is actually 1s22s22p63s23p64s13d5

Why? This gives us two half filled orbitals. Slightly lower in energy. The same principal applies to copper. Write the Cu configuration now

Copper’s electron configuration

Copper has 29 electrons so we expect

1s22s22p63s23p64s23d9

But the actual configuration is 1s22s22p63s23p64s13d10

This gives one filled orbital and one half filled orbital.

Remember these exceptions

Orbital Notation

A 3 dimensional space around a

nucleus in which electrons are most

likely to be found

Shape represents electron density (not

a path the electron follows)

Each orbital can hold up to 2 electrons.

Learning Check S5

A. Number of electrons in a p orbital1) 1e 2) 1e or 2e 3) 3e

B. Number of orbitals in a p subshell1) 1 2) 2 3) 3

C. Number of orbitals in 4d subshell1) 1 2) 3 3) 5

D. Number of electrons (maximum) in a 3d 1) 2e 2) 5e 3) 10e

Solution S5

A. Number of electrons in a p orbital

2) 1e or 2e

B. Number of orbitals in a p subshell

3) 3

C. Number of orbitals in 4d subshell

3) 5

D. Number of electrons in a 3d subshell

3) 10e

The Periodic Law

All the elements in a group have the same electron configuration in their outermost shells

Example: Group 2

Be 2, 2

Mg 2, 8, 2

Ca 2, 2, 8, 2

Learning Check EA5

Specify if each pair has chemical properties that are similar (1) or not (2):

A. Cl and Br

B. 2 - 5 and 2 - 8 - 7

C. 2 - 4 and 2 - 8 - 4

D. P and S

E. O and S

Solution EA5

Specify if each pair has chem. properties that are similar (1) or not similar (2):

A. Cl and Br 1

B. 2 - 5 and 2 - 8 - 7 2

C. 2 - 4 and 2 - 8 - 4 1

D. P and S 2

E. O and S 1

Learning Check S2

Indicate if each configuration is (1) correct or (2) incorrect for potassium. Give an explanation for selection of 1 or 2. Explain

A. 1s22s22p63s1 1 or 2

B. 1s22s22p63s23p6 1 or 2

C. 1s22s22p63s23p64s1 1 or 2

D. 1s22p83s1 1 or 2

E. 1s22s22p63s23p7 1 or 2

Solution E2

For phosphorus, indicate if each configuration is (1) correct or (2) incorrect. Explain why or why not.

A. 2, 2, 8, 5 2

B. 2, 8, 3 2

C. 2, 8, 5 1

D. 2, 6, 7 2

Learning Check S3

Using the periodic table, write the complete electronic configuration for each:

A. Cl

B. Sr

C. I

Solution S3

Using the periodic table, write the complete electronic configuration for each:

A. Cl

1s2 2s2 2p6 3s2 3p5

B. Sr

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

C. I

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

Learning Check S4

A. The final two notations for Co are

1) 3p64s2

2) 4s24d7

3) 4s23d7

B. The final three notations for Sn are

1) 5s25p24d10

2) 5s24d105p2

3) 5s25d105p2

Solution S4

A. The final two notations for Co are

3) 4s2 3d7

B. The final three notations for Sn are

2) 5s2 4d10 5p2