Chem Module 2 Flashcards
Quantization
When an electron is ‘confined’ to a finite region of space by the forces exerted on it
- total energy is restricted t certain values
Light and its three fields
electromagnetic radiation that transmits energy through space/medium, travels in waves
- electric field, magnetic field, direction that oscillate perpendicular to eachother
wavelength
distance between adjacent maxima
period
time for electric field to return to its max strength
frequency
related to period , 1/T
The electromagnetic spectrum in increaing wavelength (decreasing frequency )
gama rays, x rays, ultraviolet, visible, infrared, microwave, radiowaves
Range of visible region in nm
from 400 to 750 nm
visible spectrum and their colours
- violet (400)
- indigo
- blue
- green (570)
- yellow
- orange
- red (750)
3 experiments that support the concept of energy being quantized at the molecular level
- Blackbody Radiation
- The Photoelectric Effect
- Line Spectra of Atoms
Blackbody Radiation
- atoms in a heated solid osciallte with certain energies only
- Energy of oscillation = nhv
Max Planck
First suggestion of quantization of energy , quanta of energy are absorbed by and emitted from matter
- Frequency : v=c/landa
- Energy: E = nhv (h is an constant , v is frequency)
- plancks constant
The photoelectric effect
- Energy of light is highly localized and is proportional to its frequency
- light can produce and electric current
- discovered by having electrons dislodge from the surface of a metal
Observations of the photoelectric effect
- electrons were ejected only if the frequency of light was greater than some “threshold” frequency
- ejected electron increased proportionally with frequency
- energy of the light must be highly localized in space and not spread out over the entire wave
- proportionality constant between frequency and energy is equal to Planck’s constant
Ephoton =hv
Line Spectra of atoms
Energy of an electron in an atom is not arbitrary , restricted to certain special values.
- absorbed or emitted colours show that atoms absorb or emit photons with certain specific energies - emission lines
Problems with the Bohr Model
- doesn’t explain why the angular momentum and energy of the electron is quantized
- model not extended to other atoms
- why doesn’t the H atom emit radiation continuously?
2 solutions to the limitations of the Bohr Model (behaviour of electrons)
- de Brogile’s hypothesis
- the Heisenberg uncertainty principle
de Brogile’s hypothesis
particles exhibit wave-particle duality by understanding
- diffraction (light behaving as a wave)
- The photoelectric effect (light behaves as particles)
experiment: diffraction pattern produced by constructive and destructive interference of light waves
Heisenberg uncertainty principle
we can never know the true behaviour of a system
- if we tried to measure the position of an electron, we will change its momentum
n quantum number
principal quantum number - determines size of orbital (any integer)
l quantum number
orbital angular momentum quantum number - determines the shape of an orbital (n-1)
ml quantum number
magnetic quantum number - the number of distinct orientations allowed for a particular orbital (-l to +l)
Radial factors, what does it describe and its axis
R(r) and r, how the wave function changes w distance from nucleus
Radial electron density, what does it describe and its axis
R(r)^2 and r, probability of finding electron changes as we move away from the nucleus
Radial Distribution plot, what does it describe and its axis
r^2(R)r^2 and r, average distance between nucleus and electron
