Download Arrangement of Electrons in Atoms I. The Development of a New

Arrangement of Electrons in Atoms
I. The Development of a New Atomic Model

BIG IDEA- Electrons have properties of both WAVES & PARTICLES!
A. The Nuclear Atom and Unanswered Questions
 List three reasons scientists found Rutherford’s nuclear atomic model to be incomplete. His model did not explain
1. ______________________________________________________________________________________
2. ______________________________________________________________________________________
3. ______________________________________________________________________________________

Before the 1900’s, scientists thought light behaved only as waves. This belief changed when it was discovered that light also
has particle-like characteristics. This is known as the wave-particle duality of light.
B. Wave Nature of Light
 Electromagnetic radiation:

The electromagnetic spectrum includes:

Characteristic properties of light waves include (draw a wave below and label the parts):

The significant feature of wave motion is its repetitive nature, which can be characterized by the measurable properties of
wavelength and frequency.
1. Wavelength (m, cm, nm):
-1
2. Frequency (s or Hz):

___________________________ and ________________________ are mathematically related to each other. For
electromagnetic radiation, the relationship is…….
Formula:
Where c = speed of light =
λ=
ν=

Wavelength and frequency are _______________________________ proportional. This means
______________________________________________________________________________________

ALL electromagnetic waves travel at the speed of light (in a vacuum).

A light beam passing through a prism is refracted (bent), separating it into all of the colors of the rainbow called the
_______________________________________________________________.
1. ROYGBIV: ________________________________________________________________________________
2. Each color of light has its own _____________________ and ________________________ ; and therefore a different
amount of energy.
C. Particle Nature of Light
 Photoelectric effect:

Planck’s quantum concept (1900)
1. By studying the heating of solid objects, his quantum concept concluded that matter can gain or lose
_____________________________ only in small, specific amounts called ___________________. A quantum is the
minimum amount of energy that can be ______________________ or ________________________ by an atom.
2. A direct proportion exists between the energy of a quantum and the frequency of the emitted radiation:
Formula:
Where E= _______________________________; the unit for energy is __________________
h= Planck’s constant = _______________________________________
ν = _____________________________; the unit is ___________________

Einstein and the photoelectric effect (1905)
1. Einstein proposed that EM radiation has both wavelike and particle-like behavior. He explained that in addition to its
wavelike characteristics, a beam of light can be thought of as a stream of ____________________________ called
_____________________________.
2. Photon:
3. Einstein’s explanation of the photoelectric effect:
Practice Problems:
Problem/Work
1. Yellow light has a longer wavelength than green light. Which color of light has the higher frequency?
2. Green light has a lower frequency than blue light. What color of light has a longer wavelength?
3. Calculate the wavelength of yellow light emitted by a sodium lamp if the frequency of the radiation is
14
5.10 x 10 Hz.
-7
4. Determine the frequency of light whose wavelength is 4.257 x 10 cm.
5. Calculate the energy, in Joules, of a quantum of radiant energy (the energy of a photon) that has a
15 -1
frequency of 5.00 x 10 s .
6. A photon has energy of 2.93 x 10
-25
J. What is its frequency?
7. A hydrogen line emission spectrum includes a line at a wavelength of 434 nm. What is the energy of
this radiation?
Answer
D. Atomic Emission Spectra
Define the following:
 ground state:

excited state:

emission:

absorption:

line- (or atomic-) emission spectrum:

Each element’s atomic emission spectrum is __________________________ and can be used to identify that element.
E. Bohr’s Model of the Atom

Bohr constructed a model of the hydrogen atom with quantized energy levels that agreed with the hydrogen emission
spectrum.

Bohr’s model:
1.
2.
3.

At first, Bohr’s model appeared promising; it fit the hydrogen atom very well, BUT ________________________________
___________________________________it did NOT _______________.

Electrons do ___________ move around the nucleus in circular orbits.

His model did pave the way for later theories.
F. Quantum Mechanical Model

Mathematical laws can identify the regions outside of a nucleus where the electrons are __________________________ to
be found.

These laws are beyond the scope of this class and include the work of DeBroglie, Heisenberg, Schrodinger, and others.

Like Bohr, the quantum mechanical model lead to quantized energy levels. Unlike Bohr, the quantum mechanical model
does not define an exact pathway for electrons.
The _____________________________________________________________ is concerned with the ______________________ of
finding an electron.
Today we say that the electrons are (most probably) located in a region outside the nucleus called the
electron cloud.