Electron Configurations &

The Periodic Table

Quantum Atomic Theory

Heisenberg (1901-1976)

Schrödinger (1887-1961)

Einstein (1879-1955) Pauli (1900-1958)

Plank (1858-1947)

Bohr-Rutherford vs Quantum

Similarities• Electrons have discrete amounts of energy• Positive nucleus in the centre

Differences:

Heisenburg Uncertainty Principle– the position and magnitude of an electron cannot both be known. If one is measure, the other is altered.

Bohr-Rutherford Quantum•Atom in 2D•The location of the electrons can be predicted

•Electrons travel on circular paths around the nucleus

•Atom is 3D•The location of the electrons cannot be predicted

•Electrons move randomly in ‘clouds of probability’

Orbitals - Redefined• The Quantum model of the atom describes electrons in different

orbitals (or energy levels) around the nucleus. The traditional orbits of the Bohr model are subdivided.

• Orbital/Sub-orbital: region around the nucleus where there is a high probability of finding an electron

• The Period on the periodic table tells you the energy level, the blocks contained within that period lets you know the kinds of orbitals the atom has or where the last electrons of that element are likely to be at any given moment.

The maximum number of electrons in each type of suborbital:

s = 2 electrons maximump = 6 electrons maximum

d = 10 electrons maximumf = 14 electrons maximum

Electron Configuration & The Periodic Table

Electron configurations• Lists e- location from low to high energy

in the following format

iron atom: 1s2 2s2 2p6 3s2 3p6 4s2 3d6

So what does carbon look like?• Carbon has 6 e-, so…

• Therefore, the electron configuration of carbon is:1s2 2s2 2p2

The electron configuration of potassium is:1s2 2s2 2p6 3s2 3p6 4s1

Shorthand e- configurations

Cl: 1s2 2s2 2p6 3s2 3p5

becomesCl: [Ne] 3s2 3p5

• e- config. Is written only for the outer shell electrons

• The noble gas indicates all inner shells are full

Shorthand: [noble gas]

Energy Level Diagrams

1s

3s

2s2p

4s3p

3d

4p

5s4d

5p

6s

E

Pictorial representation of

electron distribution in

orbitals

Aufbau principle – e- occupy the lowest energy

orbital availablep. 188 in text

Hund’s rule – e- half-fill each orbital in a

sublevel before pairing up

Pauli exclusion principle – max 2 e- per orbital (spin up

and spin down)

n = 1 l = 0 ml = 0 ms = -½

Creating Energy-Level Diagrams• Pauli exclusion principle –

o no two electrons in an atom may have the same four quantum numbers

o no two electrons in the same orbital may have the same spin

o only two electrons with opposite spins may occupy an orbital

• aufbau principle – (German for “building up’)o each electron is added to the lowest available energy

orbital• Hund’s rule –

o one electron is placed in each orbital at the same energy level before the second electron is placed

Orbital Diagrams

1s 2s 2p 3s 3p

O (z = 8)

1s 2s 2p 3s 3p

P (z = 15)

1s 2s 2p 3s 3p

Ar (z = 18)

Energy Level Diagrams

1s

3s

2s2p

4s3p

3d

4p

5s4d

5p

6s

E

Anions - Add e- to lowest energy sublevel available.

Cations - Remove e- from sublevel with highest value of n.

Energy Level Diagrams

1s

3s

2s2p

4s3p

3d

4p

5s4d

5p

6s

E

Cations - Remove e- from sublevel with highest value of n.

Energy Level Diagrams

1s

3s

2s2p

4s3p

3d

4p

5s4d

5p

6s

E

Shape of orbitals• The diagram we used to represent oxygen is;

8 Proton

s-

-

-

-

-

-

-

-

8

16O

Shape of orbitals The diagram we might currently use to

represent oxygen is;

Confidence building questions

1.Write out the shorthand notation for the electron configuration of B.2.Write out the shorthand notation for the electron configuration of Cl.3.Write out the shorthand notation for the electron configuration of F.4.Write out the shorthand notation for the electron configuration of Ca.5.Write out the shorthand notation for the electron configuration of Kr.6.Write out the shorthand notation for the electron configuration of O2-. Notice that this is an anion!7.Write out the shorthand notation for the electron configuration of Na+. Notice that this is a cation!8.Why are Groups 1 and 2 referred to as the s-block of the periodic table?9.Why are Groups 3 through 12 referred to as the d-block of the periodic table?10.Using what you now know about electron configurations explain the notion that elements in the same column in the periodic table have similar chemical and physical properties.