Electrons in Atoms
Chapter 5
Electromagnetic Radiation

light exhibits wave-like behavior as it travels
through space
Parts of the Wave


Wavelength (λ) – shortest distance
between equal points on a wave
- crest to crest
- units – m, cm, or nm
Frequency (ν) – number of waves that
pass by a given point every second
- units – Hertz (Hz) or s-1
Electromagnetic Waves





All electromagnetic waves travel at a speed
of 3.00 x 108 m/s in a vacuum
Speed of light is c = 3.00 x 108 m/s
Speed is a product of wavelength and
frequency
c=λ·ν
Wavelength and frequency are inversely
related. As one increases the other
decreases
Wavelength vs. Frequency

They are inversely related:
Calculating Wavelength and Frequency





You can find wavelength or frequency
by using the speed of light equation
c=λ·ν
Ex. 1 – if the frequency of a microwave
is 3.44 x 109 solve for the wavelength.
3.00 x 108 m/s = λ · 3.44 x 109 Hz
8
3.00 x10 m / s
λ=
= 0.0872m
9
3.44 x10 Hz
Sample Problems c = λ · ν
Ex. 2 - What is the wavelength of a
ultraviolet ray that has a frequency of
4.80 x 1017 Hz?
c=λ·ν
Sample Problems c = λ · ν
c=λ·ν
3.00 x 108 m/s = λ · 4.80 x 1017 Hz
λ=
8
3.0 x10 m / s = 6.25 x 10-10m
17
4.80 x10 Hz
Sample Problems c = λ · ν
Ex. 3 - What is the frequency of a gamma
ray that has a wavelength of 7.3 x 10-9m?
c=λ·ν
Sample Problems c = λ · ν
c=λ·ν
3.00 x 108 m/s = 7.3 x 10-9 m · ν
8
3
.
00
x
10
m
/
s
ν=
= 4.10 x 1016 Hz
9
7.3x10 m
Electromagnetic Spectrum
 Electromagnetic radiation includes radio
waves that carry broadcasts to your radio
and TV, microwave radiation used to heat
food in a microwave oven, radiant heat used
to toast bread, and the most familiar form,
visible light.
 All of these forms of radiant energy are parts
of a whole range of electromagnetic
radiation called the electromagnetic
spectrum
Electromagnetic Spectrum
Homework: ch. 5
# 1- 4
# 7, 12
pg. 121
pg. 126
Atomic Orbitals


Electrons travel
around the nucleus in
definite orbitals (not on
a fixed path)
Electrons are on
different energy levels
– the higher the
energy level the farther
the electron is from the
nucleus
Atomic Orbitals
Principle
Energy Level
Sublevel
1
s
s, p
s, p, d
s, p, d, f
2
3
4-7



Energy Levels are
divided into sublevels
and orbitals
s – orbitals are shaped
like a sphere
p – orbitals are shaped
like dumbbells
• Energy level 1 is closest to the nucleus and has the
least amount of energy
Atomic Orbitals

Each orbital can hold two electrons

s - 1 orbitals
p – 3 orbitals
d – 5 orbitals
f – 7 orbitals



(2 electrons)
(6 electrons)
(10 electrons)
(14 electrons)
Electron Configurations


1.
2.
3.
The arrangement of electrons in an
atom
Three principles for filling in electron
configurations
Aufbau Principle
Pauli Exclusion Principle
Hunds Rule
Electron Configuration

Aufbau Principle
- each electron
occupies the lowest
energy orbital
available
- energy diagram
pg. 135
Electron Configurations

Pauli Exclusion Principle
- we use arrows to represent electrons
- electrons spin in two different
directions (up and down) ↑↓
- maximum of two electron per orbital
Electron Configurations
Hund’s Rule
- single electrons w/ the same spin must
occupy each orbital in a sublevel
before additional electrons with
opposite spins can occupy the same
orbital
- do example on board

Orbital Diagrams

Represent an atom’s electron
configuration by drawing a box for
each orbital and arrows for the
electrons
Electron Configuration Notation
Designates the principle energy level
1, 2, 3….7
 Designates the energy sublevel
s, p, d, or f
 Includes a superscript representing the # of
electrons in each sublevel
Examples
C – 1s2 2s2 2p2
N - 1s2 2s2 2p3

Electron Configuration Notation
sample problems
Na –
1s2 2s2 2p6 3s1
2+2+6+1 = 11
1s2 2s2 2p6 3s2 3p3
2+2+6+2+3 = 15
P–
Br –
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p5
Rb 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s1
Noble Gas Configuration

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


Ne – 1s2 2s2 2p6
Na – 1s2 2s2 2p6 3s1
Al - 1s2 2s2 2p6 3s2 3p1
Use Noble gases for a shorter way to write out the
electron configuration
Use brackets to represent the noble gas and then
add in the rest of what you need
Na – [Ne] 3s1
Al – [Ne] 3s2 3p1
Noble Gas Configuration
sample problems
K–
[Ar] 4s1
Pt –
[Xe] 6s2 4f14 5d8
N–
[He] 2s2 2p3
Valence Electrons



The electrons in the outermost energy
level are called valence electrons
Valence electrons are the electrons that are
involved in chemical bonding and determine
the properties of an element
All representative elements in the same
group have the same number of valence
electrons
Valence Electrons
Write the e- configuration for the following: P, Be,
O, Al, Cl, and Ar
P- 1s2 2s2 2p6 3s2 3p3
Be – 1s2 2s2
O – 1s2 2s2 2p4
Al – 1s2 2s2 2p6 3s2 3p1
Cl – 1s2 2s2 2p6 3s2 3p5
Ar – 1s2 2s2 2p6 3s2 3p6
- 5 v.e.
- 2 v.e.
- 6 v.e.
- 3 v.e.
- 7 v.e.
- 8 v.e.
Valence Electrons



The elements number of valence
electrons is equal to their group A #
An element may never have more than
eight valence electrons
Because valence electrons are so
important to the behavior of an atom, it
is useful to represent them with
symbols (Dot Diagrams)
Dot Structures


The symbol of the element with dots
around it to represent the valence
electrons (no more than 8 dots)
Fill one dot on each side and then put
two on all sides (no more than 8 dots)
Dot Structures
Write a Lewis dot diagram for each of the
following.
1. Chlorine
7 v.e.
2. Calcium
2 v.e.
3. Potassium
1 v.e.
Dot Structure of the
Representative Elements
Dot Structure of the
Representative Elements