Development of Atomic Models. Democritus. Greek philosopher 400 BC “ Atomos ” concept. Can matter can be divided forever? Eventually, a piece would be “indivisible” “ Atomos ,” meaning “not to be cut , ” is smallest piece of matter. John Dalton (early 1800’s).
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Dalton’s Atomic Theory called
“Hard Spheres Model”
Lets draw a typical Crooke’s Tube in our notes.
Cathode Ray Tube and Magnet
They bent toward (+) plate
Cathode Rays were particles
They couldn’t pass through matter.
Atoms are positively charged spheres with negatively charged particles scattered throughout.
Thompson and Discovery of Electron
Identify the charge each type of radiation has.
Rutherford Gold Foil
Most alpha particles passed straight
through gold foil.
Atom’s volume is mostly empty space.
A few alpha particles
deflected at an angle
or bounced back.
Atoms have a very
small, dense positively
Nucleus is extremely small compared to the size of the atom as a whole.
Deflections happened rarely (1/8000).
Modern Example of Gold Foil Experiment in Action
Rutherford’s Model is called the “Nuclear Model”
Brian Cox: Rutherford and the Nucleus
2n2 = maximum number of electrons an energy level can hold.
Ex: Level 3 can hold 2(3)2 = 18 electrons
Human Bohr Model
(+) ions are smaller
(-) ions are larger
Video of Line Spectra of Hydrogen
Electrons normally exist in the lowest energy level possible called the “ground state”. (stable)
“Ground state” e- configurations are written on the periodic table for each element.
Ex: Aluminum is 2-8-3
Calcium is 2-8-8-2
Electrons can absorb a photon (or “quanta”) of energy and “jump up” to a higher energy level farther from the nucleus.
This is called the “excited state”. (unstable)
Model Of Hydrogen Atom and Electrons Jumping
Phosphorus is 2-8-5
and 3 valence electrons
Wavelength (λ): distance between two peaks of a wave
Frequency (γ): number of peaks that pass per second. (Hertz (Hz) or cycles/sec)
Which wave has higher energy?
If you know the wavelength of the spectral line you can find it’s frequency.
c = λ x ү
c = the speed of light = 3 x 108 meters/sec
λ = wavelength (in meters)
ү = frequency of the wave
Using the frequency find the energy of the line (in Joules)
E = h x ү
E = energy in Joules
h = Planck's constant = 6.63 × 10-34 kg x m2 / sec
ү = frequency of the wave