Download Chapter 5: Electrons in Atoms

Chapter 5: Electrons in
Atoms
REVISING THE ATOMIC MODEL
ELECTRON ARRANGEMENT IN ATOMS
ATOMIC EMISSION SPECTRA AND THE QUANTUM MECHANICAL MODEL
Learning Targets
You will:
1. Determine the energy levels,
sublevels and orbitals of
electrons in an atom.
2. Determine how to write
electron configuration and
orbital notation for atoms and
ions.
Atom Models …

Rutherford: couldn’t explain chemical properties
of elements

Bohr: explained how energy levels of electrons in
an atom change when the atom emits light

Schrodinger: devised and solved mathematical
equation describing electron behavior in atom

Restricts energy of electrons to certain values

Doesn’t specify exact path electron takes around
nucleus

Calculations show previous models didn’t always
correctly describe electron motion
You will determine the energy levels, sublevels and orbitals of electrons in an atom.
Quantum Mechanical Model

Probability of finding an electron
represented as fuzzy, cloudlike region

Cloud more dense when probability
high

Atomic orbital is pictorially a region of
space where high probability of finding
electron
You will determine the energy levels, sublevels and orbitals of electrons in an atom.
Quantum Mechanical Model

Energy levels labeled by principal
quantum numbers (n) and
assigned values of 1, 2, 3, 4 and so
on

Energy levels within principal
energy level are sublevels

Each sublevel corresponds to one
or more orbitals of different shapes
You will determine the energy levels, sublevels and orbitals of electrons in an atom.
Summary of energy levels and sublevels
You will determine the energy levels, sublevels and orbitals of electrons in an atom.
Atomic Orbitals


Principal quantum number, n, = #
sublevels w/in principal energy
level
# orbitals in principal energy level
= n2

Maximum of 2 electrons can
occupy an orbital

Maximum number of electrons
that can occupy an energy level =
2n2
Example:

Calculate the maximum number
of electrons in the 5th principal
energy level (n = 5).

The maximum number of electrons
that can occupy a principal
energy level is given by the
formula 2n2.

If n = 5, 2n2 = 50.
You will determine the energy levels, sublevels and orbitals of electrons in an atom.
Sublevels and Energy Levels
You will determine the energy levels, sublevels and orbitals of electrons in an atom.
Table talk …
What causes atomic emission
spectra?

When atoms absorb energy, their
electrons move to higher energy
levels. These electrons lose
energy by emitting light when
they return to lower energy levels.

No two elements have the same
emission spectrum.
You will determine the energy levels, sublevels and orbitals of electrons in an atom.
You will determine the energy levels, sublevels and orbitals of electrons in an atom.
What we saw in the lab …
Nature of light
c = ln

Amplitude = wave’s height from
zero to crest

Wavelength = distance b/t crests

Frequency = # wave cycles to pass
given point/unit of time

Frequency and wavelength
inversely proportional

Product of frequency and
wavelength = constant (c), speed
of light
Nature of Light

Electromagnetic radiation
includes radio waves,
microwaves, infrared waves,
visible light, ultraviolet
waves, x-rays and gamma
rays

All waves travel at a speed
of 3.00 x 108 m/s
Example
 Calculate
the wavelength
of the yellow light emitted
by a sodium lamp if the
frequency of the radiation
is 5.09 × 1014 Hz (5.09 ×
1014/s).
c
=ln
𝑐
 =l
𝑣
3.00 x 10^8 m/s

5.09 x 10^14 Hz
 5.89
=l
x 10-7 m = l
Try on your own
What
is the
frequency of a
red laser that has
a wavelength of
676 nm?


c=ln
𝑐
l
=n
1m
 676 nm 
1 x 10^9 nm
3.00 x 10^8 m/s

=n
6.76 x 10^−7 m

4.44 x 1014 Hz = n
= 6.76 x 10-7 m
Quantum Concept and photons

German physicist Max Planck
showed mathematically that the
amount of energy (E) absorbed or
emitted is proportional to the
frequency of radiation (n).

The constant (h) has a value of
6.626 x 10-34 Js and is called
Planck’s constant
Example
 What
is the energy of a
photon of microwave
radiation with a
frequency of 3.20 ×
1011/s?
E
=hn
 E = 6.626 x 10-34 Js
 3.20 x 1011/s
 E = 2.12 x 10-22 J
Try on your own
 What
is the frequency
of a photon whose
energy is 1.166 x 10–17
J?
E
=hn
𝐸
 =n
ℎ
1.166 x 10^−17 J

6.626 x 10^−34 Js
 1.760
=n
x 1016 Hz = n
Table talk …
What are the three rules for
writing the electron
configurations of elements?

Three rules—the aufbau
principle, the Pauli
exclusion principle, and
Hund’s rule—tell you how to
find the electron
configurations of atoms.

Aufbau principle: electrons occupy orbitals of
lowest energy first before filling higher energy levels

Pauli exclusion principle: two electrons must have
opposite spins to occupy the same orbital


Spin is a quantum mechanical property of electrons

A vertical arrow indicates an electron and its
direction of spin
Hund’s rule: every orbital is singly occupied with
one electron before any orbital is doubly
occupied, all electrons in singly occupied orbitals
have the same spin.
You will determine how to write electron configuration and orbital notation for atoms and ions.
Electron Configurations

Convenient shorthand
method involves writing
energy level and symbol
for every sublevel, then
indicate the number of
electrons w/superscript

Sum of the superscripts = #
electrons in atom
You will determine how to write electron configuration and orbital notation for atoms and ions.
Electron Configurations
You will determine how to write electron configuration and orbital notation for atoms and ions.
Examples
Write the electron
configuration for the
following atoms:
Answers:
1. 1s1
1.
hydrogen
2. 1s2 2s2 2p3
2.
nitrogen
3.
aluminum
3. 1s2 2s2 2p6 3s2 3p1
You will determine how to write electron configuration and orbital notation for atoms and ions.
Electron Configurations
You will determine how to write electron configuration and orbital notation for atoms and ions.
More Examples
Write the electron
configuration for the
following atoms:
Answers:
1. 1s2
1.
helium
2. 1s2 2s2 2p4
2.
oxygen
3.
silicon
3. 1s2 2s2 2p6 3s2 3p2
You will determine how to write electron configuration and orbital notation for atoms and ions.
Electron Configurations
You will determine how to write electron configuration and orbital notation for atoms and ions.
Try on your own
Write the electron
configuration for the
following atoms:
1. sodium
2. phosphorus
3. potassium
Answers:
1.1s2 2s2 2p6 3s1
2.1s2 2s2 2p6 3s2 3p3
2
2
6
2
6
1
3.1s 2s 2p 3s 3p 4s
You will determine how to write electron configuration and orbital notation for atoms and ions.
Electron Configurations
You will determine how to write electron configuration and orbital notation for atoms and ions.
Orbital Notation

Orbital notation is a way of
drawing electron configurations

A box or blank indicates the
space for an orbital

Remember an orbital can hold
two electrons

An orbital will correspond to each
energy level and sublevel in the
configuration
You will determine how to write electron configuration and orbital notation for atoms and ions.
Examples
Write the orbital notation
for the following atoms:
1. Sulfur
2. Silicon
3. Magnesium
You will determine how to write electron configuration and orbital notation for atoms and ions.
Electron Configurations

Electron Configuration and Orbital Notation change for
elements after the first 20.

This is because instead of going in order of each energy level
and sublevel, we jump from the 4s to 3d

An example of an electron configuration with this: Se 1s22s22p63s23p64s23d104p4

Notice the jump from 4s to 3d then back to 4p
You will determine how to write electron configuration and orbital notation for atoms and ions.
Examples

Give the electron configuration for gallium (Ga), bromine (Br) and
hafnium (Hf).
Ga
– 1s22s22p63s23p64s23d104p1
Br - 1s22s22p63s23p64s23d104p5
Hf - 1s22s22p63s23p64s23d104p65s24d105p66s24f145d2
You will determine how to write electron configuration and orbital notation for atoms and ions.
Try on your own

Give the electron
configurations for the
following elements:
1.
tin (Sn)
2.
lead (Pb)
3.
polonium (Po)
4.
iodine (I)
tin (Sn) pollonium (Po) –
1s22s22p63s23p64s23d104p65s24d105p2 1s22s22p63s23p64s23d104p65s24d105p66s24
lead (Pb) f145d106p4
1s22s22p63s23p64s23d104p65s24d105p66s24 iodine (I) f145d106p2
1s22s22p63s23p64s23d104p65s24d105p5
You will determine how to write electron configuration and orbital notation for atoms and ions.
Orbital Notation

Pick one atom from the last set of problems and write its orbital notation
You will determine how to write electron configuration and orbital notation for atoms and ions.
Summarize how you feel …
You will:
1. Determine the energy levels,
sublevels and orbitals of
electrons in an atom.
2. Determine how to write
electron configuration and
orbital notation for atoms and
ions.