The Quantum Model of the Atom

What atoms really look like.(We Think?)

The Bohr Atom

• The Bohr model of the atom has electrons orbiting the nucleus in orbit that we call energy levels. Electrons are particles like little planets going around the nucleus.

• Electrons can move between energy levels absorbing or giving off light.

• Called atomic spectra.

Emission spectra“atomic finger prints”

A problem with Bohr’s atom.

• Electrons traveling in an orbit should give off light continuously … they don’t.

• Why?• Bohr didn’t know, his model just

worked.

What are electrons?

– 1924: De Broglie said that electrons were waves containing specific amounts of energy (like Bohr’s energy levels)

– But no one said that they weren’t still a particle

Heisenberg Uncertainty Principle

• We can only observe electrons by interaction with photons. Interactions with photons cause electrons to move.

• Problem?

• 1927 – Heisenberg says: we can’t know where an electron is AND where it is going at the same time.

Quantum Theory

• 1926: Erwin Schrödinger calculated electrons as waves and found only specific energies worked (once again, just like Bohr)

Solve!

Orbital• A three dimensional space around the nucleus where

an electron is likely to be found.• Described by Schrodinger equation as a probability of

finding the electron.

Quantum Numbers

• Tell us where electrons are LIKELY TO BE based on energy states of electrons.

• There are 4 numbers to describe each electron.• The 1) energy level, 2) the sub level, 3) the orbital

and 4) the spin.

• Pauli exclusion principle: no two electrons in the same atom can have the same four quantum numbers

1) Energy Level

• “principle quantum number”

• Indicates main energy level just like Bohr’s model

• There are 7 energy Levels• As n increases, so does the

energy and distance from nucleus

2) The Sub Level

• Describes the SHAPE• There are 4 shapes

• The specific orbital the electron is in.• s has 1, p has 3, d has 5, f has 7

3) The Orbital

s orbitals are spherical

p orbitals are dumbell shaped

d orbitals are complex

f orbitals are really complex

4) The Spin

• For each orbital there are two spins: up and down.

• Thus, each orbital contains two electrons

s= electron

Up spin

Down spin

p= electron

downup

down

upup

down

d= electron

up

down

f

14 electrons total!

How are orbital shapes related to the energy levels

s p d f

n = 1 1s

n = 2 2s 2p

n = 3 3s 3p 3d

n = 4 4s 4p 4d 4f

n = 5 5s 5p 5d 5f 5g

n = 6 6s 6p 6d 6f 6g 6h

n = 7 7s 7p 7d 7f 7g 7h

n = 8 8s 8p 8d 8f 8g 8h

As energy level goes up, orbitals get bigger!

• 2s is larger than 1s

• 3p is larger than 2p• 3s is larger 2s etc.

Sub Level

Number of Orbitals in the

Sub Level

Number of Electrons

Needed to Fill Sub Level

Total Number of Orbitals in the Energy Level

n2

Total Number of Electrons in Energy Level

2n2

1s 1 2 1 2

2s 1 2

2p 3 6 4 8

3s 1 2

3p 3 6

3d 5 10 9 18

4s 1 2

4p 3 6

4d 5 10

4f 7 14 16 32

The Periodic Table

• Remember: # of electrons = atomic number• Where does each electron go?

• Electron Configuration: Arrangement of electrons in an atom.

Rules!

• Aufbau principle: an electron occupies the lowest-energy orbital that it can.

• Hund’s Rule: orbitals of equal energy are each occupied by one electron before any orbital is occupied by a second electron.

1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, and 7p

Lowest E Highest E

Six boys move into a new house.

Hydrogen

1s

= electron

Helium

1s

Lithium

1s

2s

Beryllium

1s

2s

Boron

2s

2p

1s

Carbon

1s2s

2p

Nitrogen

1s2s

2p

Oxygen

1s2s

2p

Fluorine

1s2s

2p

Neon

1s2s

2p

Orbital Notation

1s

2s 2p

Hydrogen

1s1

2s 2p

Electron Configuration

1s

Helium

1s

2s 2p

1s2Electron Configuration

Lithium

1s

2s 2p

1s22s1Electron Configuration

Beryllium

1s

2s 2p

1s22s2Electron Configuration

Boron

1s

2s 2p

1s22s22p1Electron Configuration

Carbon

1s

2s 2p

1s22s22p2Electron Configuration

Nitrogen

1s

2s 2p

1s22s22p3Electron Configuration

Oxygen

1s

2s 2p

1s22s22p4Electron Configuration

Fluorine

1s

2s 2p

1s22s22p5Electron Configuration

Neon

1s

2s 2p

1s22s22p6Electron Configuration

Noble Gas Configuration

• To help you be lazy!• Write noble gas in [ ] that precedes the

element. Then only write electrons that exist thereafter.

• The electron configuration for Heliumis NOT [He]!

1 H 1s1

2 He 1s2

3 Li [He]2s1

4 Be [He]2s2

5 B [He] 2s2 2p1

6 C [He] 2s2 2p2

7 N [He] 2s2 2p3

8 O [He] 2s2 2p4

9 F [He] 2s2 2p5

10 Ne [He] 2s2 2p6

11 Na [Ne] 3s1

12 Mg [Ne] 3s2

13 Al [Ne] 3s2 3p1

14 Si [Ne] 3s2 3p2

15 P [Ne] 3s2 3p3

16 S [Ne] 3s2 3p4

17 Cl [Ne] 3s2 3p5

18 Ar [Ne] 3s2 3p6

19 K [Ar] 4s1

20 Ca [Ar] 4s2

21 Sc [Ar] 4s2 3d1

22 Ti [Ar] 4s2 3d2

23 V [Ar] 4s2 3d3

24 Cr [Ar] 4s1 3d5

25 Mn [Ar] 4s2 3d5

26 Fe [Ar] 4s2 3d6

27 Co [Ar] 4s2 3d7

28 Ni [Ar] 4s2 3d8

29 Cu [Ar] 4s1 3d10

30 Zn [Ar] 4s2 3d10

31 Ga [Ar] 4s2 3d10 4p1

32 Ge [Ar] 4s2 3d10 4p2

33 As [Ar] 4s2 3d10 4p3

34 Se [Ar] 4s2 3d10 4p4

35 Br [Ar] 4s2 3d10 4p5

36 Kr [Ar] 4s2 3d10 4p6

Exceptions!

• Half filled orbital sets are happy!

• Completely filled orbital sets are happy!