Download Electromagnetic Radiation

ELECTROMAGNETIC RADIATION
Ms. Marshall
Chemistry
WW-P
PROPERTIES OF RADIATION

How does electromagnetic energy present itself?

What parameters can be measured?

How was quantum theory developed?
QUANTUM THEORY
Einstein’s Photoelectric Effect
 What is the photoelectric effect?
The frequency of radiation is
what matters – not the intensity
 Nobel prize in 1919
 Experimental support Planck’s quantum theory.
 Quantum is a “packet” or “bundle” of energy
 Wave-particle duality – radiation has properties
of both particles and waves

RADIATION PROPERTIES



Radiation is classified as electromagnetic energy
Electromagnetic radiation is energy traveling through
space that has wave-like properties.
Parameters: frequency (ν), wavelength (λ),
amplitude, energy (E)
What is the
relationship
between λ and ν?
How are both
variables related
to E?
All ER waves
travel at the
speed of light!!
2.998 x 108 m/s.
WHY DOES THIS MATTER?
Atomic structure was identified by looking at
spectra
 because they are unique we can identify elements
based on their spectra
 We use what we have learned about the atoms
using their spectra to classify them in the
Periodic Table

ELECTROMAGNETIC SPECTRUM
Source: Wilbraham, A.C., et. Al. Chemistry, 2005
ESSENTIAL QUESTION

Why don’t atoms give off a continuous spectra?
BOHR’S MODEL OF THE ATOM
1913 – Rutherford’s Nuclear Model of the atom
was changed.
 New discoveries about how the energy of an atom
changes when it absorbs or emits light were
included
 Bohr’s model is based on Hydrogen atoms only
 Proposed that electrons travel only in
specific circular paths, or orbits, around the
nucleus.
 Worked well for Hydrogen, not for other atoms.

BOHR’S MODEL OF THE ATOM

Each possible e- orbit has a fixed energy called
energy levels
CHECK FOR UNDERSTANDING

A.
B.
C.
D.
If an electron absorbs energy to change energy
levels, how much energy will it absorb.
Less than the amount of energy of the “new”
energy level
More energy than the amount of energy
required for the “new” energy level
Just enough energy to have the same energy as
the “new” energy level
An amount of energy equal to the energy of the
new energy level
BOHR’S MODEL OF THE ATOM
The amount of energy an e- gains or loses will not
always be the same.
 Energy levels are not equally spaced
 This model failed to explain the energies
absorbed and emitted for atoms other than
hydrogen.

THE QUANTUM MECHANICAL MODEL

Erwin Schrodinger
Based on new theoretical calculations and
experimental results
 Created and solved a mathematical equation
describing the behavior of the e- in an H atom


Quantum mechanical model
The modern description, primarily
mathematical, of the behavior of electrons in
atoms
 comes from solutions to Schrodinger’s equation

QUANTUM MECHANICAL MODEL

Differences from Bohr’s Model


Not an exact path for the e- to travel around the
nucleus
Determines the allowed energies an e- can have
and the probability of finding the e- in a location

Described by probability (4 marble examples)
How do these pictures relate to the probability of an e- being in certain
place?
Think-Pair-Share (1.5 minutes)
WHAT IS QUANTUM MECHANICS

1905 – Albert Einstein
 Explained experimental data that proposed that light
could be described as quanta of energy.
Photons – a quantum of light;
 1924 – Louis de Broglie
 Light behaves as waves and particles, so can particles
of matter behave as waves?
 1927 – Clinton Davisson & Lester Germer @ Bell
Labs in NJ (confirmed de Broglie’s hypothesis)
 Noticed that e- reflected from metal surfaces when
bombarded with beams of e-.
 Odd patterns – like x-rays reflecting from metal
surfaces.

WHAT IS QUANTUM MECHANICS?
Reflected as if they were waves.
 This property of particles is used to create clear,
enlarged images of very small objects.
 Size of object needs to be very small to observe
the wavelength.

WHAT IS QUANTUM MECHANICS?

Classical mechanics


Describes the motions of objects much larger than
atoms adequately
Quantum mechanics

Describes the motion of subatomic particles and
atoms as waves
HEISENBERG UNCERTAINTY PRINCIPLE

Werner Heisenberg (German physicist)
It is impossible to know exactly both the velocity and
position of a particle at the same time.
 Does not apply to large objects


Cars, airplanes
ATOMIC ORBITALS
Solving Schrodinger’s equation tells you the
energies an e- can have.
 Also leads to a mathematical expression
 atomic orbital

A region of space in which there is a high
probability of finding an electron
 Determined by the solutions to Schrodinger’s
equation.

WHERE ARE THE ELECTRONS ?
Ground state – most stable region closest to
nucleus
 Excited state – when energy is applied, electron
absorbs energy and jumps to a region farther
away from the nucleus; the electron immediately
returns to stable ground state and emits energy
(in the form of light)

ATOMIC ORBITALS

Principal quantum numbers (n)
Labels for energy levels
 n = 1, 2, 3, 4, …

Each principal energy level can have a number of
orbitals with different shapes at different energy
levels. (sublevels)
 Key Point


Each energy sublevel corresponds to an orbital
of a different shape, which describes where the
electron will most likely be found.
SUBLEVELS

Due to the spherical shape of the s orbital, the
probability of finding an e- at a given distance
does not depend on direction.
SUBLEVELS
SUBLEVELS
ELECTRONS!!!
If all atoms are composed of the
same fundamental building
blocks, how is it that different
atoms have vastly different
chemically behaviors?