history of the atom jj thomson neils bohr earnest rutherford albert einstein

HISTORY OF THE ATOM

JJ ThomsonNeilsBohr

EarnestRutherford

AlbertEinstein

JJ Thomson- Plum Pudding Model

Electrons are scattered throughout a positively charged body.

DISCOVERY OF RADIATION

• Radioactive Material- unstable material that emits high energy electromagnetic waves or particles when broken down.

• Henri Becquerel-1896- discovered radiation is emitted from uranium.

Marie Curie- isolated polonium and radium• “Neither of us could foresee that in beginning this

work we were to enter the path of a new science which we should follow for all our future.”

Ernest Rutherford-1911- determined that there are 3 types of radiation

Alpha Particles (α)- Helium nucleus. ( 24He )

Beta Particle (β)- High speed electron (0-1e )

Gamma Rays (γ)-High energy electromagnetic wave moving at the speed of light.

RUTHERFORD GOLD FOIL EXPERIMENT

Alpha particleshttp://www.youtube.com/watch?v=Q8RuO2ekNGw

GOLD FOIL EXPERIMENT Most particles passed through foil without

deflection. Indicated that the atom is mostly empty space.

Some particle were deflected backwards. Indicated that the atom has a central (+) mass.

Few deflections occurred at large angles. Indicated that the nucleus is small and dense.

Electrons don’t have enough mass OR charge to change the path of the alpha particle

RUTHERFORD MODEL OF THE ATOM

Small, dense, positively charged nucleus.

Electrons are located outside the nucleus.

GOLD FOIL LIMITATIONSDidn’t identify entire mass. (1932 Chadwick

found the neutron)Didn’t explain why the electrons aren’t

attracted to the nucleus, which would cause the atom to collapse.

Didn’t account for light emission as electrons orbit.

Didn’t account for different spectrums of light produced by different atoms.

Maxwell Planck-1900- Proposed that light is an electromagnetic

wave that forms bundles of energy called photons. This brought about the idea of the dual nature of light and led to further investigation of

the atom

Neils Bohr 1927• Developed the planetary model of the atom

where the electrons orbit the nucleus in fixed positions without radiating light.

Bohr Model The (+) nucleus and (-) electrons give the

atom its energy. As distance from the nucleus increases, more

energy is needed to hold electrons in orbit. Atoms emit a photon when an electron drops

to a lower energy level. Energy of the emitted photon is equal to the

change in energy levels.

Ionization energy- the energy needed to move an electron to ground state. The (-) value indicates the electron energy is controlled by the nucleus.

On reference table

If electrons move to a higher energy level, they absorb a photon.

If they drop to a lower energy level they give off energy in the form of light.

Photon energy

Ephoton = Ei – Ef

Ei = initial level Ef= final level

unit: eV (electronvolts) or J (joules)

1 eV= 1.6 x 10-19J

Ex- An electron falls from the 2nd energy level to ground state of a hydrogen atom. If it gives off a photon, what is the energy of the photon?

Ephoton = -3.4eV − -13.6eV = 10.2ev

Ephoton = (10.2eV)(1.6 x 10-19 J/eV)

Ephoton = 1.63 x 10-18 J

Spectrum- the light pattern given off when a photon is emitted.

Lyman Series- electron moves to ground state. (ultraviolet range)

Balmer Series- electron falls to 2nd energy level.(visible light)

Paschen Series- Electron falls to the 3rd energy level( Infrared range)

Bohr Model LimitationsLimited electrons to specific levels.Didn’t explain how the electrons could have

centripetal acceleration without extra energy.

Goes against Newton’s Laws

DeBroglie Model-1924- Showed that the electrons orbit the nucleus in a wave pattern. Doesn’t account for electrons between orbitals

Cloud Model- Erwin Schrodinger- instead of levels, electrons are located in areas of high or low probability called energy states

High probability

LowProbability

Albert Einstein-1905

Proposed that the mass of a body is the measure of its energy content. This could help explain model limitations and showed a mass discrimination in the atom.

Einstein’s energy equation E = m c2

E- energy (Joules) c- speed of light m- mass (kg) 3 x 108 m/s

Ex) What is the energy content of a 70kg student? E = 70kg(3x108)2

E = 6.3 x 1018 J

Ex) What is the mass of a subatomic particle having 0.66eV of energy? a) First convert eV to joules: E= 0.66eV(1.6 x 10-19 J/eV) E = 1.056 x 10-19 J

b) Then Use E=mc2 : 1.056 x 10-19 J = m (3x108m/s)2

m= 1.17 x 10-36 kg

Ex: What is the energy content of a carbon atom in eV and Joules?a) Atoms are measured in AMU (atomic mass

units) 1AMU= 931MeV Carbon has a mass of 12 AMU E= 12 AMU(931MeV/AMU) E = 11,172 MeV

b) 1 MeV = 1x106eV E= 11172MeV(1x106eV/MeV) E = 1.1172 x 1010 eV

c) 1 eV = 1.6 x 10-19 J E = 1.1172 x 1010 eV( 1.6x10-19 J/eV) E = 1.78 x 10-9J