Transcript Electron Excitement Notes

Electron Excitement Notes
The Atom and Unanswered Questions
Recall that in Rutherford's model, the atom’s mass is concentrated in
the nucleus and electrons move around it.
The model doesn’t explain how the electrons were arranged around the
nucleus.
The model doesn’t explain why negatively charged electrons aren’t pulled
into the positively charged nucleus.
The Atom and Unanswered Questions (cont.)
In the early 1900s, scientists observed certain elements emitted visible
light when heated in a flame.
Analysis of the emitted light revealed that an element’s chemical behavior
is related to the arrangement of the electrons in its atoms.
The Wave Nature of Light
Visible light is a type of electromagnetic radiation, a form of energy that
exhibits wave-like behavior as it travels through space.
All waves can be described by several characteristics.
The Wave Nature of Light (cont.)
The wavelength (λ) is the shortest distance between equivalent points
on a continuous wave.
The frequency (ν) is the number of waves that pass a given point per
second.
The amplitude is the wave’s height from the origin to a crest.
The Wave Nature of Light (cont.)
The Wave Nature of Light (cont.)
The speed of light (3.00  108 m/s) is the product of it’s wavelength and
frequency
c = λν.
The Wave Nature of Light (cont.)
Light exists with varying amounts of frequencies (# of waves per
second) and wavelengths (distance between each wave)
Shorter wavelength/ Higher frequency corresponds to more energy,
the opposite to less energy
Sunlight contains a continuous range of wavelengths and frequencies.
A prism separates sunlight into a continuous spectrum of colors.
The electromagnetic spectrum includes all forms of electromagnetic
radiation.
The Wave Nature of Light (cont.)
• --Visible light is light
that has a wavelength
within the range of
10-6 to 10-7 meters. If
light has a longer
wavelength, the color
will be closer to red,
and if light has a
shorter wavelength,
the color will be closer
to violet.
• R O  Y  G  B
IV
• Light outside of the range of visible light cannot
be detected by the human eye.
• Generally any light with more energy than visible
light is called Ultraviolet, and that with less
energy is Infrared
Atomic Emission Spectra
Light in a neon sign is produced when electricity is passed through a
tube filled with neon gas and excites the neon atoms.
The excited atoms emit light to release energy.
• When electrons are where they are
predicted to be (from order in periodic
table), they are considered to be in their
ground state.
• Sometimes atoms will absorb energy (ex.
from electricity) and their electrons are
given enough energy for them to “jump” to
a higher energy level. This is considered
an excited state.
• Eventually they will
lose the energy and
fall back down to their
ground state from the
excited state.
• When this falling
occurs, the electrons
emit the lost energy in
the form of light.
• When the electrons
fall, they will release a
color of light that will
correspond to the
amount of energy that
is released from the
fall.
• The minimum amount of energy needed to
make an electron jump is called a
quantum. If an atom receives less than a
quantum of energy, no light will be emitted
• The light emitted will be in the form of a
specific “particle” called a photon. It can be
thought of as a “bundle” of energy
• The longer the
fall, the more
energy is
released, and the
closer the color
will be to violet.
• If the fall is short,
there is less
energy released,
and the color is
closer to red.
• Each element has a different number of
electrons and therefore a different number
of possible energy level changes.
• Also, the spacing between orbitals varies
with each element
• Because of this, when each element is
excited, the colors of light that will be
released will vary.
Atomic Emission Spectra (cont.)
Atomic Emission Spectra (cont.)
The atomic emission spectrum of an element is the set of frequencies
of the electromagnetic waves emitted by the atoms of the element.
Each element’s atomic emission spectrum is unique.
• By comparing the
spectrum with known
values, the type of
element that is
emitting the light can
be determined.
• For instance, this
shows four tubes
containing different
gases (neon,
mercury, helium, and
hydrogen)
• A Spectroscope
• It bends light to
separate the
colors that are
found in within the
light into different,
distinct colors in
different locations
• When their light is
shown through a
spectroscope,
different colors
appear in different
places for each
different element