Atom

28.1 THE BOHR MODEL

Ernest Rutherford directed positvely - charged, high-speed alpha particles at thin metal foils .
By studying the paths of the reflected particles, he showed that atoms are mostly empty spaced with a tiny , massive, postively-charged nucleus at the center.
The spectra produced by atoms of an element can be used to identify that element .
If white light passes through a gas , the gas absorbs the same wavelengths it would emit if exicted.
If light leaving the gas goes through a prism , an absorption spectrum is seen.
In the model of the atom developed by Niels Bohr , the elctrons are allowed to have only certain energy levels.
In the Bohr Model, electrons can make transitions between energy levels .
As they do , they emit or absorb electromagnetic radiation.
The frequency and wavelength of the absorbed and emitted radiation can be calculated using the Bohr model .
The calculations agree with experiments.

28.2 THE PRESENT MODEL OF ATOM

The quantum, mechanical model of the atom cannnot be visualized easily .
Only the probability that an electron is at a specific location can be calculated.
Quantum mechanics is extremely successful inh calculating the Properties of
atoms , molecules, and solids.
Lasers produce light that is directional , powerful monochromatic , and coherent.
Each property gives the laser useful appilication.

1- alpha particles - is postively charged particles which consist of two protons and
two neutrons.

2-absorption spectrum - is a spectrum of electromagnetic radiation that absorbs
all the radiation when frequency pass through it.

3- Bohr Model - understands the structure of the atom , also it calcuates the emission
spectrum , and the ionization enrgy of a hydrogen atom.

4- electron cloud - is the region of high probabilty of finding an electron in an atom.

5-emission spectrum- is the spectrum that produces radiation in the excited state.

6- energy levels - is the amount of energy that an electron has in an atom.

7- excited state- is the energy level of atom in a higher than ground state.

8-ground state - is the lowest energy level of an electron .

9-laser - is the devise that produces light by stimulating emission of radiation.

10- nuclear model - is Rutherford's model of the atom.

11-quantized - quantity that cannot be divided&nbbsp; into small increments forever ,
the minimum of the quantum increment .

12- quantum mechanics - study of the properties of matter uses the wave properties.

13-quantum model of atom - atomic model in which the probability of electron is known.

14-quantum number - integer ratio of energy to its quantum increment.

15-spectroscope- device that is used to study spectrum of material .

16- stimulated emission - emission of photon from exicted atom caused by impast of photon of same energy .

Fc= mac

Kq squared /r squared= mv squared/r squared

rn= h squared / 4( pie) squared KmQsquared X n squared

En= -2(pie) squared K squared mq to fourth powwer /h squared X 1/n squared

En= -2.17 X 10 to -18 powerJ (1/n squared)>

En= -13.6 eV(1/n squared)

hf= delta E

hr/wavelength l =nh/ 2(pie)

THE ATOM