ARRANGEMENT OF ELECTRONS IN ATOMS

The Development of a New Atomic Model - 4.1

The Old Atomic Model Problem with Rutherford model

– no explanation of where e-s are

New info about light led to new model of the atom

Before 1900 scientists thought light traveled like a wave.

We know now that light behaves like a wave and like a particle

The Wave Description Called the dual wave-particle nature

of light! Electromagnetic Radiation - form of

E that exhibits wavelike behavior as it travels thru space

Electromagnetic Spectrum - all of the forms of electromagnetic radiation (visible light, x-rays, uv and infrared light, micro and radio waves)

The Wave Description

All types of emag rad. move at 3.00 x 108 m/s in a vacuum. (slightly slower thru matter)

This is the speed of light

The Electromagnetic Spectrum

Wavelength and Frequency Wavelength - λ the distance

between corresponding points on adjacent waves

Frequency - ν the number of waves that pass agiven point in a specific time, usually 1 second

Frequency is expressed in Hertz (Hz)

The Relationship B/T Freq. and Wavelength

c = λν The speed of light = wavelength

times frequency The wavelength of red light is

7.6 x 10-7 m, calculate the frequency.

F = speed      =  2.998 x 108 m/s wavelength            7.6 x 10-7 m

Frequency = 3.9 x 1014Hz

The Photo-electric Effect The emission

of e-s from a metal when light shines on the metal

Light had to be a certain freq. to emit e-s

The Particle Description of Light

Planck proposed idea of quanta (E packets)

Quantum of energy - the minimum quantitiy of E that can be lost or gained by an atom

The Particle Description of Light

E = hν Where E is the energy in

joules of a quantum of radiation

υ is the frequency in s-1

h is Planck's constant of 6.626 x 10-34 J *  s

Einstein and the dual particle-wave nature

Ein. supported Planck by proposing the duality of light as particle and wave

Ein. proposed particles of light carry a quantum of E called photons (0 mass)

Einstein and the dual particle-wave nature

The E of a photon depends on the υ of rad.

E absorbed in whole # of photons

Different metals need diff. υ to remove an e-

The H atom and the LES

Electric current passed thru a gas at a low pressure

The Line Emission Spectrum

LES = the resultfrom a narrowbeam of theemitted light thatis shined througha prism when itseparated intocolors of thevisible spectrum

The Continuous Spectrum

E Levels

Ground state - the lowest E level of an atom (very stable level)

Excited state - a state in which an atom has a higher potential E than it has in its ground state

E Levels

When an e- falls from the excited state, a photon is given off - the E of the photon is = to the E difference

H only emits certain freq. so e- exists in specific E levels