Chemistry Notes Chapter 8
Chemistry Notes Chapter 8 •
End of 19th century, it was believed that everything about classical physics was known. Only a few unsolvable problems remained
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Electromagnetic radiation- form of energy transformation in which electric and magnetic fields are propagated as waves through empty space (a vacuum) or through as medium, such as glass.
•
Amplitude- maximum height of the wave above the center line or the maximum depth below
•
Wavelength- distance between the tops of two successive crests (or bottom of 2 troughs). Designated by lambda:
•
Frequency- number of crests or troughs that pass through a given point per unit of time. Unit: s-1 = hertz(Hz). Designated by nu:
•
Product of a wave (lambda) and the frequency (nu) shows how far the wave front travels in a unit of time
•
Electromagnetic waves are transverse waves
•
1 nanometer (nm) =1x10-9m=1x10-7cm=10 angstrom
•
1 angstrom
•
1 picometer (pm) = 1x10-12m=1x10-10cm=10-2 angstrom
=1x10-10m=1x10-8cm=100 pm
•
Speed of light is 2.998x10-8 m/s, represented by the letter c
o
C=
x
o
Speed of light is different in different media. Light is refracted (bent) when it passes from one medium to another. Thus, when a beam of white light is passed through a transparent medium, the wavelength components are refracted differently, creating a spectrum.
•
In phase waves, constructive interference, out of phase, destructive interference
•
Diffraction- dispersion of light into its different components as a result of interference produced by the reflection of light from a grooved surface
•
Continuous spectrum-light being diffracted consists of many wavelength components
•
Discontinuous spectrum- light being diffracted consists of a relatively small number of wavelength components
•
Atomic (or line) spectra-produced by dispersing light emitted by excited gaseous atoms. Only a discrete set of wavelength components is present.
•
Balmer’s equation:
= 3.2881x1015s-1(1/22 – 1/n2)
o
Nu=frequency of the spectral line
o
n=integer greater than 2
•
Classical physics could not provide a complete explanation of light emission by heated solids, a process known as blackbody radiation
•
1900- Planck said: Energy, like matter, is discontinuous.
•
Quantum theory limits energy to a discrete set of specific values
•
Quantum of energy- difference between 2 allowed energies of a system
•
Planck’s constant: h= 6.62607x10-34Js
•
Planck’s equation: E= h o
•
States that energy of quantum of electromagnetic radiation is proportional to the frequency of the radiation higher frequency=greater energy
1888- Hertz discovered that when light strikes the surface of certain metals, electrons are ejected photoelectric effect. Electron emission occurs when the frequency of the incident light exceeds a particular threshold value. When this condition is met: o
Number of electrons emitted depends on the intensity of the incident light, but
o
Kinetic energies of the emitted electrons depend on the frequency of the light
•
1905- Einstein proposed that electromagnetic radiation has particlelike qualities and that “particles” of light (photons) have characteristic energy given by Planck’s equation.
•
Photon of energy strikes a bound electron, which absorbs the photon energy. If the photon energy is greater than the energy binding the electron to the surface (work function), a photoelectron is liberated. Thus, lowest energy frequency light producing the photoelectric effect is the threshold frequency and any energy in excess of the work function appears as kinetic energy in the emitted electron.
•
Stopping voltage (Vs)- kinetic energy of the photoelectrons has been converted to potential energy, expressed through the following equation (m=mass, u=speed, e=charge of electron): 1/2mu^2=eV s
•
At frequencies greater than
End of 19th century, it was believed that everything about classical physics was known. Only a few unsolvable problems remained
•
Electromagnetic radiation- form of energy transformation in which electric and magnetic fields are propagated as waves through empty space (a vacuum) or through as medium, such as glass.
•
Amplitude- maximum height of the wave above the center line or the maximum depth below
•
Wavelength- distance between the tops of two successive crests (or bottom of 2 troughs). Designated by lambda:
•
Frequency- number of crests or troughs that pass through a given point per unit of time. Unit: s-1 = hertz(Hz). Designated by nu:
•
Product of a wave (lambda) and the frequency (nu) shows how far the wave front travels in a unit of time
•
Electromagnetic waves are transverse waves
•
1 nanometer (nm) =1x10-9m=1x10-7cm=10 angstrom
•
1 angstrom
•
1 picometer (pm) = 1x10-12m=1x10-10cm=10-2 angstrom
=1x10-10m=1x10-8cm=100 pm
•
Speed of light is 2.998x10-8 m/s, represented by the letter c
o
C=
x
o
Speed of light is different in different media. Light is refracted (bent) when it passes from one medium to another. Thus, when a beam of white light is passed through a transparent medium, the wavelength components are refracted differently, creating a spectrum.
•
In phase waves, constructive interference, out of phase, destructive interference
•
Diffraction- dispersion of light into its different components as a result of interference produced by the reflection of light from a grooved surface
•
Continuous spectrum-light being diffracted consists of many wavelength components
•
Discontinuous spectrum- light being diffracted consists of a relatively small number of wavelength components
•
Atomic (or line) spectra-produced by dispersing light emitted by excited gaseous atoms. Only a discrete set of wavelength components is present.
•
Balmer’s equation:
= 3.2881x1015s-1(1/22 – 1/n2)
o
Nu=frequency of the spectral line
o
n=integer greater than 2
•
Classical physics could not provide a complete explanation of light emission by heated solids, a process known as blackbody radiation
•
1900- Planck said: Energy, like matter, is discontinuous.
•
Quantum theory limits energy to a discrete set of specific values
•
Quantum of energy- difference between 2 allowed energies of a system
•
Planck’s constant: h= 6.62607x10-34Js
•
Planck’s equation: E= h o
•
States that energy of quantum of electromagnetic radiation is proportional to the frequency of the radiation higher frequency=greater energy
1888- Hertz discovered that when light strikes the surface of certain metals, electrons are ejected photoelectric effect. Electron emission occurs when the frequency of the incident light exceeds a particular threshold value. When this condition is met: o
Number of electrons emitted depends on the intensity of the incident light, but
o
Kinetic energies of the emitted electrons depend on the frequency of the light
•
1905- Einstein proposed that electromagnetic radiation has particlelike qualities and that “particles” of light (photons) have characteristic energy given by Planck’s equation.
•
Photon of energy strikes a bound electron, which absorbs the photon energy. If the photon energy is greater than the energy binding the electron to the surface (work function), a photoelectron is liberated. Thus, lowest energy frequency light producing the photoelectric effect is the threshold frequency and any energy in excess of the work function appears as kinetic energy in the emitted electron.
•
Stopping voltage (Vs)- kinetic energy of the photoelectrons has been converted to potential energy, expressed through the following equation (m=mass, u=speed, e=charge of electron): 1/2mu^2=eV s
•
At frequencies greater than
