Electrons in Atoms

•Rutherford’s model

-Shows where protons & neutrons are

-Not good at showing the location of electrons

Light Energy

•When elements are heated, they are excited & jump up to a higher energy level. In doing so, they give off a color of light.

•Each element gives off a unique color called its atomic emission spectrum.

•The electrons are what give each element their unique color.

•Light gives us a clue to how electrons are arranged.

•Light behaves like a wave & like a particle.

Light Energy

•Light in wave form is called an electromagnetic wave, & is part of the electromagnetic spectrum which includes x-rays, TV waves, microwaves, radio waves, UV waves & gamma waves.

Light Energy

Wave StructureTrough – low points Crest – high points

Wavelength – the shortest distance between points in which a wave repeats itself. (crest to crest or trough to trough) symbol - λ

Amplitude – max displacement from equilibrium (middle of wave).

crest

Parts of a Wave•Wavelength - of one wave, from a crest to a crest or trough to a trough•Symbol = λ ( ) •Measured in

•Frequency- number of waves that pass a point in 1 second•symbol = v ( )

•Measured in (Hz)

length

lambdameters

nuHertz

•Formula: c = λ v

c is constant speed of light

v is frequency

λ is wavelength

•All EM radiation travels at the speed of light, c = 3.00 x 108 m/s in the vacuum of space

Calculations

Microwaves are used to transmit information. What is the wavelength of a microwave having a frequency of 3.44 x 109 Hz?

Known

v= 3.44 x 109 Hzc = 3.00 x 108 m/s

Unknown

λ= ? m

c = λv

λ= c/v

•λ= 3.00x 108/ 3.44 x 109

•Answer: 8.72 x 10-2m

What is the frequency of green light, which has a wavelength of 4.90 x 10-7m

An X ray has a wavelength of 1.15 x 10-

10m. What is the frequency?

•Light as a particle is called a photon.

•Light is like a particle because there are only certain amounts of energy it can have.•The minimum amount of energy a photon can have is called a quantum.

Light Particles

•Max Planck found that this energy could be calculated with the formula E = h ν

•Once the minimum amount of energy is calculated, the actual energy can be a multiple of the quantum amount. (1x E, or 2 x E, or 3 x E....)

•v is frequency (Hz or 1/s)

•h is Planck’s Constant = 6.626 x 10-

34 Js

•E is energy, measured in Joules (J)

Light Particles

Water drops in the air disperse the white light of the sun into a rainbow. What is the energy of a photon from the violet portion of the rainbow if it has a frequency of 7.23 x 1014Hz?

Known

v = 7.23 x 1014 s-1

h = 6.626 x 10-34 J s

Unknown

Ephoton = ? J

Ephoton= (6.626 x 10-34J s)(7.23 x 1014 s-1)

• Cancel the units

• Answer: 4.79 x 10-19J

What is the energy of each of the following types of radiation?

a. 6.32 x 1020s-1

b. 9.50 x 10 13 Hz

c. 1.05 x 10 16 s-1

•Electrons (called photoelectrons) are emitted from a metal’s surface when light of a certain frequency shines on the surface.

•Example: calculators.•Photoelectric cells convert light into electric energy

Photoelectric Effect

•Niels Bohr in 1913 proposed a quantum model for the hydrogen atom which correctly predicted the frequencies of the lines (colors) in hydrogen’s atomic emissions spectrum.

Bohr Model

•His model gave atoms only certain allowable energy states.

•The lowest state is called the ground state.

•When an atom gains energy it is said to be in an excited state.

Bohr Model

•Bohr also said that the motion of the electron relates to its energy state. That electrons move around the nucleus in certain allowed circular orbits.

•The smaller the orbit, the lower the energy state.

Bohr Model

•Bohr assigned each energy level a quantum number, n.

•There are only 7 energy states.

Bohr Model

•The 7 energy states are like rungs on a ladder, electrons can move up or down the ladder from rung to rung, but there is no “in between”.

•An electron can only move from one allowable orbit to another and can only emit or absorb certain amounts of energy.

Bohr Model

The 1st energy level can hold only 2 e-, 2nd 8e-, 3rd 8e-, 4th 18e-, 5th 18e-, 6th 32e-

remember these #’s 2-8-8-18-18-32!

Ex: Draw the Bohr model for Fluorine

# of Protons =

# of Electrons = # of neutrons =

9

910

e- e-

e-

e-

e-e-

e-e-

e-

nucleus

Bohr Model

Draw the Bohr Model for Ni

• # of e- =

28

e-

e-

e-

e-

e-

e-e-

e-e-

nucleus

1st level = 2e-2nd level = 8e-

e-

3rd level = 8e- e-

e-

e-

e-

e-

e-e-

e-

4th level = 10e-

e-

e-

e-e-e-

e-

e-

e-

e-e-

Draw the Bohr model for the following elements:Co F Br Ag