Download The atom and unanswered questions: Bohr`s model did not address

The atom and unanswered questions:
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Bohr’s model did not address the differences and similarities in chemical behavior among the
various elements.
In the early 1900’s, chemists observed that certain elements emitted visible light when heated
in a flame or exposed to other energy sources.
Analysis of the emitted light revealed that this behavior was related to the electron
arrangement within its atoms.
In order to understand this relationship, we must first review the nature of light.
The only differences among the different types of waves making up the electromagnetic spectrum
are the frequencies and wavelengths.
1) Wavelength (represented by λ) is the shortest distance between equivalent points on a continuous
wave. Wavelength is usually expressed in meters or nanometers (1 nm = 1 x 10-9 m)
2) Frequency (represented by ν) is the number of waves that pass a given point per second. Frequency
is measured in hertz, Hz. One hertz equals one wave per second.
Relationship between frequency and wavelength:
What do you notice about the relationship between the frequency and the wavelength of a wave?
It is an inverse relationship: as the frequency increases the wavelength decreases.
3) All electromagnetic waves, including visible light, travel at a speed of 3.00 x 108 m/s in a vacuum. This
value is often referred to as the speed of light (and is represented by c).
Speed of light = frequency x wavelength
C = νλ
Practice problems:
1.
Calculate the wavelength of the yellow light emitted by the sodium in the pickle if the
frequency of the radiation is 5.10 x 1014 Hz.
c = νλ
3.00 x 108 = 5.10 x 1014 (λ)
λ = 5.88 x 10-7 m or 588 nm
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The red-colored light given off by the compound held in the flame has a wavelength of
6.50 x 10-7 m. What is the frequency of such red light?
c = νλ
3.00 x 108 = ν 6.50 x 10-7
V = 4.62 x 1014 Hz
Planck’s constant
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Planck demonstrated mathematically that a relationship exists between the energy of a
quantum and the frequency of the radiation that is emitted.
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Planck’s constant (h) = 6.626 x 10 -34 J (the joule, J, is a unit of energy)
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Energy = Planck’s constant x frequency (E = hν)
Practice Problem:
1. What is the energy of a photon from the violet portion of the Sun’s light if it has a frequency of
7.23 x 1014 Hz.
E = hν
E = 6.626x10-34 X 7.23 x 1014
E = 4.79 x 10-19J
Bohr’s model of the atom and the particle nature of light
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Recall that Bohr stated that electrons exist on energy levels.
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When enough energy is added to an atom, electrons jump to a higher energy level.
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(This is sometimes referred to as a “quantum leap” or the electrons are said to be in an
excited state)
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This is an unstable situation and the electron will drop back to its former energy level, the
ground state, releasing the absorbed energy in the form of light.
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The color of light emitted depends on what energy level an electron is dropping to.
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A revision in Bohr’s model of the atom was necessary to explain the relationship among atomic
structure, electrons, and the unique frequencies of light emitted.