1. Chapter 7 The Quantum-Mechanical Model of the Atom (7.1-7.3)
By Liad Elmelech (Mr. Elmelech)

2. The nature of Light Light has properties of both waves and particles
Light is electromagnetic radiation
Energy of fluctuating electric and magnetic fields
Magnetic field - area were magnetic particles experience a force
Electric field – are regions were electrically charged particles experience a force
Travels at 3.00*10^8 m/s (on reference table)

3. Characterizing a wave Amplitude Height of crest or depth of trough
Determines brightness
Greater amplitude increases intensity
Wavelength (λ)
Length between crests
Determines color of visible light
Colors in order of increasing wavelengths
Red, orange, yellow, green, blue, indigo, violet
Frequency (v)
Number of crests that pass through a point at in a given period of time
Units: cycles per second (cycle/s or s^-1)
Hertz(Hz) = 1 cycle/s

4. Equation for frequency and wavelength of light
c = λv (on reference table)
c is speed of light
Calculate the wavelength, in nm, emitted by a barcode scanner that has a frequency of 4.62 * 10^14 s^-1.
Nanometer = 10^-9 meters
λ= c/v
λ= (3.00*10^8m/s) / (4.62*10^14/s)
λ= 6.49*10^-7m
λ= 6.49*10^-7m * 1nm/10^-9m = 649nm

5. The electromagnetic spectrum
In order of decreasing wave lengths / increasing frequency –radio,
microwaves, infrared, visible light, ultraviolet, X-ray ,Gamma Ray
Ultraviolet radiation, X-rays, and gamma rays can damage biological molecules

6. Infrared radiation
Associated with transitions in molecular vibrations
Can be used to detect presence of different types of bonds
Ultraviolet / visible radiation
Associated with transitions in electronic energy levels
Can be used to probe electronic structure

7. Interference Constructive interference
When two waves of equal amplitude are in phase when they interact a wave with twice the amplitude results (in phase means that they align with overlapping crests)
Destructive interference
If two waves that are out of phase interact the waves cancel

8. Photoelectric effect
Many metals emit electrons when light shines on them
If frequency is too low than no electrons are emitted
Einstein: “light energy must come in packets”
E=hv (on reference table)
E is the amount of energy in a light packet (also called a photon, or quantum)
v is frequency
h is the Plank’s constant
6.626*10^-34 Js (on reference table)
v =λ/ c, therefore, E = hc / λ
Diffraction
Not purely a wave
Light is a shower of particles

9. A nitrogen gas laser pulse with a wavelength of 337 nm contains 3
A nitrogen gas laser pulse with a wavelength of 337 nm contains 3.83 mJ of energy. How many photons does it contain? (number of photons = Epulse / Ephoton)
λ= 337nm*(10^-9m/1nm) = 3.37*10^-7m
E Photon = hc / λ = ((6.626*10^-34 J*s)(3.00*10^8 m/s)) / (3.37*10^-7m)
=5.8985*10^-19 J
3.83 mJ *(10^-3 J / 1 mJ) = 3.83*10^-3 J
Epulse / Ephoton = (3.83*10^-3) / (5.8985*10^-19)
=6.49*10^15 photons

10. More about the photoelectric effect - Emissions of electrons from metal depends on whether a photon has enough energy to dislodge a single electron. This energy is ionization energy.
Threshold frequency reached when energy of a photon (hv) = binding energy(φ)
hv = φ
Low frequency light does not eject electrons because no single photon has enough energy to dislodge
Energy of a photon that is beyond what is needed to dislodge an electron is transferred to the electron in the form of kinetic energy
KE = hv – φ
Wave – particle duality of light
Sometimes light behaves like a particle, at other times like a wave

11. Atomic Spectroscopy
The study of electromagnetic radiation absorbed and emitted by atoms
When an atom absorbs energy it often reemits that energy as light
Different elements emit light of different colors
Emission spectrum
A series of lines created by passing light through a prism
The emission spectrum of a particular atom is always the same
Can be used to identify an element
Niels Bohr attempted to create a model of the atom that explains the atomic spectra

12. The Bohr Model Electrons travel around the nucleus in circular orbits
Exist only at fixed distances from the nucleus
Fixed energy at each orbit (stationary state)
Radiation is emitted or absorbed when electrons jump from one orbit to another
The shorter jumps between stationary states produce light of lower energy
Eventually replaced by the quantum – mechanical theory
Do electrons in the current atomic model have fixed paths?
No, they travel in there orbitals