Transcript Chapter 5

Chapter 5
Electrons in Atoms
Anything in black letters = write it in
your notes (‘knowts’)
5.1 – Revising the Atomic Model
Rutherford’s Planetary Model of the Atom
Electrons 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.
To move from one energy level
to another, an e- must gain or
lose a quantum of energy.
Niels Bohr
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
Electrons are likely to be
found in electron ‘clouds’
around the nucleus
Electron cloud
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
s
p
d
f
Types of
Maximum Electron
Orbital
Capacity
x2
2
1
3
x2
6
x2
5
10
x2
7
14
Each orbital can hold 2 emaximum
This chart is on page 132
Summary of Principal Energy Levels and Sublevels
Energy
Level
Number of
Sublevels
n=1
1
1s (1 orbital)
2
n=2
2
2s (1 orbital), 2p (3 orbitals)
8
n=3
3
3s (1 orbital), 3p (3 orbitals),
3d (5 orbitals)
18
4
4s (1 orbital), 4p (3 orbitals),
4d (5 orbitals), 4f (7 orbitals)
n=4
Type of Sublevel
Maximum Number of
Electrons in Energy Level
32
5.2 – Electron Arrangement in Atoms
Aufbau Principle –
e- occupy the orbitals of lowest energy first.
Pauli Exclusion Principle –
Hund’s Rule –
we will not cover
Aufbau Diagram (p. 135)
6p
5d
6s
5p
4d
5s
Increasing energy
4f
4p
3d
4s
3p
3s
2p
2s
E- fill the lowest energy orbitals first
Notice the 4s fills before the 3d
1s
Another Aufbau Diagram
(write this one down!)
Orbital
Maximum Number of
e- Due to Orbitals
s
p
2
6
d
f
10
14
Aufbauprinzip, (german)
"building-up principle”
Electron Configuration –
shows how e- are arranged in an atom
Example: Nitrogen
How many e-?
7
Which orbitals fill first and how many e- can
go into each orbital? See aufbau diagram
Write the electron configuration for N
# of e- in orbitals
2
2
3
1s 2s 2p
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 Model
The Electromagnetic Spectrum (p. 139)
Low energy
( = 700 nm)
Frequency  (s-1)
3 x 106
102
High energy
( = 380 nm)
3 x 1012
3 x 1022
10-8
10-14
A prism separates light into the colors it contains.
White light produces a rainbow of colors.
Screen
Light
bulb
Slit
Prism
Light from a helium lamp produces discrete lines.
Screen
Slit
Helium
lamp
Prism
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 Quiz
1. 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