Chapter 5Chapter 5

Electrons in AtomsElectrons in Atoms

Anything in black letters = write it in your notes (‘knowts’)

5.1 – Revising the Atomic Model5.1 – Revising the Atomic Model

Rutherford’s Planetary Model of the AtomElectrons moving around a tiny nucleus

Problems with Rutherford’s Model

1.Did not explain the chemical properties of the elements.

2.Did not explain atomic spectra (…later…)

3.e- would spiral into the nucleus, but they don’t

The Bohr Model ~1913

Electrons are found only in specific locations (or orbits) around the nucleus.

These orbits are called energy levels.

Niels Bohr

To move from one energy level to another, an e- must gain or lose a quantum of energy.

The energy levels in atoms are unequally spaced, like the rungs in this unusual ladder. The higher energy levels are closer together.

The Quantum Mechanical Model

The modern description of e- in atoms.

Similar to Bohr Model except the exact location of an electron is impossible

Electron cloud

Electrons are likely to be found in electron ‘clouds’ around the nucleus

Atomic orbital –

Most probable place for e- to be.

Each orbital can hold 2 e- maximum.

The orbitals are named s, p, d & f

S (1 type) p (3 types)

d (5 types)

There are 7 types of f orbitals

Don’t worry about these shapes…

Orbital

Name

Types of Orbital

Maximum Electron Capacity

s 1

p 3

d 5

f 7

Each orbital can hold 2 e- maximum

x 2

x 2x 2

x 2 2

6

10

14

Summary of Principal Energy Levels and Sublevels

Energy Level

Number of Sublevels

Type of SublevelMaximum Number of

Electrons in Energy Level

n = 1 1

n = 2 2

n = 3 3

n = 4 4

This chart is on page 132

1s (1 orbital)

2s (1 orbital), 2p (3 orbitals)

3s (1 orbital), 3p (3 orbitals),

3d (5 orbitals)

4s (1 orbital), 4p (3 orbitals),

4d (5 orbitals), 4f (7 orbitals)

2

8

18

32

5.2 – Electron Arrangement in Atoms5.2 – Electron Arrangement in Atoms

Aufbau Principle –

e- occupy the orbitals of lowest energy first.

Pauli Exclusion Principle –

Hund’s Rule –

we will not cover

Incr

ea

sin

g e

ne

rgy

6s

5s

4s

3s

2s

1s

6p

5p5d

4p

4d

4f

3p

3d

2p

E- fill the lowest energy orbitals first

Notice the 4s fills before the 3d

Aufbau Diagram (p. 135)

Another Aufbau Diagram

(write this one down!)

Aufbauprinzip, (german) "building-up principle”

Orbital Maximum Number of e- Due to Orbitals

s 2

p 6

d 10

f 14

Electron Configuration –

shows how e- are arranged in an atom

Example: Nitrogen

How many e-?

Which orbitals fill first and how many e- can go into each orbital?

Write the electron configuration for N

1s2 2s 2p2 3

7

See aufbau diagram

# of e- in orbitals

Your turn…

Write the electron configuration for

a) boron

b) silicon

c) sulfur

Can you see how the periodic table can be used as an Aufbau Diagram?

5.3 – Atomic Emission Spectra and the Quantum Mechanical Model5.3 – Atomic Emission Spectra and the Quantum Mechanical Model

The Electromagnetic Spectrum (p. 139)

Low energy( = 700 nm)

High energy( = 380 nm)

Frequency (s-1)3 x 106 3 x 1012 3 x 1022

102 10-8 10-14

A prism separates light into the colors it contains. White light produces a rainbow of colors.

Light bulb

Slit Prism

Screen

Light from a helium lamp produces discrete lines.

SlitPrism

Screen

Helium lamp

The lines that result are unique for each element and are called its atomic emission spectrum.

Bohr’s Model explained the emission spectra

When an atom absorbs energy an electron jumps to a higher energy level (excited state).

The electron returns to the lower energy level, emitting a photon with a definite energy.

The photon’s energy shows up as a line in the emission spectrum.

Chapter 5 Quick Quiz1. Explain the main difference between the Bohr Model and the

Quantum Model of the atom.

2. How many electrons can be an atomic orbital?

3. How many types of s, p, d, and f orbitals are there?

s = ______, p = _______, d = ______, f = ______

4. What is the maximum e- capacity of the

s orbitals ____, p orbitals ____, d orbitals ____, f orbitals ____

5. Write the electron configuration for the following elements.

a) Helium

b) Strontium

c) Aluminum

d) Chlorine

e) Silver

f) Arsenic

Chapter 5 Things to Know…Rutherford Bohr Quantum Mechanical Models,

Energy Levels, Atomic Orbitals (s, p, d, f) ,

Aufbau Principle & Diagram,

Electron Configurations,

Explanation of Atomic Emission Spectra