Chapter 5

Models of the

Atom

Bohr’s model…• Electrons are found in specific circular

paths (orbits) around the nucleus. • The electrons have fixed energies called

energy levels. (like rungs on a ladder)• The amount of energy required to move

an electron to another energy level is called a quantum.

The Quantum Mechanical model

• It is based on the energy and possible location of an electron.

• how likely it is to find an electron is described in terms of probability. (ie. Propeller blades)

• Based on work done by Shrodinger…

Atomic Orbitals

• The energy levels of electrons are labeled by principal quantum numbers (n)

• Each energy sublevel corresponds to an orbital of a different shape, which describes where the electron is likely to be found.

Atomic Orbitals

Shapes and Orientations of

Orbitals

1s Orbital

• Sphere around the nucleus

The one tells you that the electron is in the orbital closest to the nucleus

• S tells you about the shape

2s Orbital

• Similar to 1s except the electron is most likely in the region farther from the nucleus

p Orbitals

• At the first energy level there is only the 1s orbital, after the second energy level there are 2p orbitals

• Look like dumbbells • In the three directions

Remember….MAX NUMBER OF ELECTRONS

IN AN ENERGY LEVELENERGY LEVEL MAX # OF ELECTRONS

1 22 83 184 325 50

Electron Configuration

A detailed way of showing the order in which electrons fill in

around the nucleus

Electron Configuration Symbols1s 2

Energy Level Sub Level

(s, p, d, f )

# of e- in sub level

We must follow 3 rules…

• Aufbau priciple• Electrons occupy energy levels with lowest

energy first.

Pauli exclusion principle

• If 2 electrons occupy the same energy level they must have opposite spins.

Hund’s rule…

• Electrons that occupy orbitals of the same energy will have the maximum number of electrons with the same spin.

• 2p

To start we will use orbital filling diagrams to help us with electron

configurations….• ExampleBoron- has 5 electrons

Periodic table arrangement

• the quantum theory helps to explain the structure of the periodic table.

• n - 1 indicates that the d subshell in period 4 actually starts at 3 (4 - 1 = 3).

s (n) d (n - 1) p (n)1234567

f (n -2)

•Practice!!!

Summary: p orbitals and d orbitalsp orbitals look like a dumbell with 3 orientations: px, py, pz (“p sub z”). Four of the d orbitals resemble two dumbells in a

clover shape. The last d orbital resembles a p orbital with a donut wrapped around the middle.

1st Quantum #Principle Quantum #

(n)Specifies the energy level

that the electron is on.

2nd Quantum #Specifies the shape of the

sub level .

(l)

The 3rd (m) and 4th quantum numbers (s) …

• Deals with the orbital within the sublevel and the spin of the electron.

Four Energy Sub-LevelsEnergy Level Sub-level Type of sub # of

Orbitalss Sphere 2 1

p Dumbbell 6 3

d 4-Lobed 10 5

f 6-8 Lobed 14 7