The Quantum Model of the Atom

Intro to Quantum Mechanics

Electrons as Waves• Louis de Broglie (1924)

– Applied wave-particle theory to electrons

– Electrons exhibit wave properties

QUANTIZED WAVELENGTHS

Quantum Mechanics• Heisenberg Uncertainty Principle

– Impossible to know both the velocity and position of an electron at the same time

Quantum Mechanics

σ3/2 Zπ

11s 0

eΨ a

• Schrödinger Wave Equation (1926)

– Finite number of solutions quantized energy levels

– Defines probability of finding an electrons

Quantum Mechanics

Radial Distribution CurveOrbital

• Orbital (“electron cloud”)

– Region in space where there is 90% probability of finding an e-

Electron Structure

• Electrons arranged into energy levels.– Names like “n=1” and “n=2”.

n = 1n = 2n = 3n = 4

Nucleus Mor

e E

nerg

y

Principal Energy Levels

Energy level (n)

Maximum Number of Electrons

1 2

2 8

3 18

4 32

Electron Structure

• Energy levels are divided into sublevels.– Sublevels within an energy level have similar

energy.

s, p, d, and f orbitals

Electron Structure

• Sublevels are made of orbitals.– Each orbital can hold up to 2 electrons.

Sublevel Orbitals Electrons

S 1 2

P 3 6

D 5 10

F 7 14

Valence Electrons• Valence electrons – Electrons in an atom’s highest-

numbered energy level.• You can tell how many valence electrons any atom should

have by its position in the periodic table.

12 3 4 5 6 7

82

variable

Lewis Dot Diagrams

• Lewis Dot Diagram – shows the valence electrons of an atom.– First 2 electrons paired on one side.– Remaining electrons are placed on other sides.– Should never have more than 8 dots.

Lewis Dot Diagrams

• Here are the Lewis diagrams for 8 elements, which have 1 – 8 valence electrons.

Li Be B C N O F Ne