A Brief History of the Atom & Atomic Models

480 B.C. aGreek philosopher Theorized everything was made out of tiny particles – atoms

Believed that atoms were hard, solid spheres that could not be destroyed

Idea was controversial - had no evidence - no one believed him.

Democritus

Democritus

“The good things of life are produced by learning with hard work; the bad are reaped of their own accord, without hard work."

"Fame and wealth without intelligence are dangerous possessions."

John Dalton English school teacher Formed his own

atomic theory. Elements made of tiny

particles -atoms. Atoms cannot be

created or divided into smaller particles.

Atoms of a an element are different from those of any other element.

John Dalton Had evidence to support his idea - Democritus did not.

Viewed the atom as a hard, solid spheres - could not be broken down.

This theory was disproved by the discovery of electrons

J.J. ThompsonDiscovered electron by using the cathode ray tube.

Cathode rays were stream of (-) charged particles.

J.J. Thompson Model had (+) and

(-) charges scattered throughout the atom.

Known as chocolate chip cookie model.

This model was disproven by discovery of the nucleus. Plum Pudding model

Ernest Rutherford Discovered nucleus by the Gold Foil Experiment.

Angles of deflection that alpha particles (+) made proved evidence of a nucleus.

Ernest Rutherford

Model defines location and charge of nucleus – doesn’t clearly define location of the electrons.

This model is IMPROVED by the Bohr model.

Niels Bohr Model depicts atom as small, (+) charged nucleus surrounded by electrons in orbit.

Similar to the solar system, but with forces providing attraction, rather than gravity.

Bohr’s model This model states that

an electrons occupy specific positions around the nucleus.

He stated that the electrons are confined to these orbits.

They can “jump” to another orbit only if some form of energy is given to that electron

Bohr’s model was found to be slightly inaccurate.

The idea of an electron actually flying around in little circles turned out to have lots of problems

Electrons have both particle and wave properties.

Particles or Waves?

Einstein theorized that light and matter exhibit properties of both waves and of particles.

This theory helps explain the idea that electrons have characteristics of waves and particles.

In order to better understand the atomic structure, it is helpful to understand waves and the nature of light

All waves can be described by several characteristics.

Wave-Particle Duality Theory

Waves Some characteristics of waves are wavelength,

frequency, amplitude and speed. Wavelength (λ) is the shortest distance between

equivalent points on a continuous wave. Amplitude is the height of the wave from the

origin to the crest or the origin to the trough.

Waves Frequency (ν) is the number of waves that

pass a given point per second. It is measured in hertz (Hz)

Frequency is expressed as “waves per second,” (1/s) or (s-1)

652 Hz = 652 waves/second = 652 s-1

Frequency and Wavelength Frequency and wavelength are inversely related As the wavelength increases, frequency

decreases Frequency is an indication of energy. Which wave has the greatest wavelength? The greatest frequency?

32

All electromagnetic waves travel at the same speed of 3.00 x 108 m/s

The speed of light (c) is the product of its wavelength (λ) and frequency (ν).

c = λ ν Because all light moves at the same speed,

it is possible to identify the wavelength or frequency of any wave.

Waves

What is the wavelength of a wave with a frequency of 5.00 x 1012 Hz ?

c = λ νc = 3.00 x 108 m/s ν = 5.00 x 1012 Hz

3.00 x 108 m/s = ( λ ) (5.00 x 1012 s-1)

λ = 3.00 x 108 5.00 x 1012 λ = 6.00 x 10-5 m

Example

What is the frequency of a wave having a wavelength of 3.33 x 10-8 m?

What is the speed of a wave with a frequency of 1.33 x 1017 Hz and a wavelength of 2.25 x 109 m?

What is the wavelength of a wave having a frequency of 7.6 x 106 Hz?

More Examples

9.01 x 1015 Hz

3.00 x 108 m/s

39.5 m

Light is a type of electromagnetic radiation. Electromagnetic radiation is a form of energy

that exhibits wavelike behavior at it travels through space.

Different types of electromagnetic radiation are distinguished by their wavelengths

Visible light from the sun, microwaves that cook our food, X rays that doctors use, and waves that carry radio and T.V. programs are all forms of electromagnetic radiation.

Wave Nature of Light

We are familiar with all the colors of visible light from our everyday experiences.

If you have ever seen a rainbow, you have seen all the visible colors at once.

The various colors that we see correspond to specific wavelength and frequency

White light, a form of visible light, contains a continuous range of wavelengths and frequencies.

Visible Light

White Light When sun light, one

example of white light, passes through a prism it is separated into a continuous spectrum of colors.

The spectrum is called continuous because all portions of light correspond to a unique wavelength and frequency.

The Visible Light Spectrum

• What color has the greatest wavelength?• What color has the greatest energy?

Visible light is one part of the electromagnetic spectrum.

EM spectrum encompasses all forms of electromagnetic radiation ordered by their wavelength and frequencies.

EM spectrum contains radio and TV waves, Microwaves, infrared rays, ultraviolet rays, X rays, and gamma rays.

Electromagnetic Spectrum

Electromagnetic Spectrum

Electromagnetic Spectrum

Which type of EM radiation are the highest in energy?

Which type has the highest wavelength? Which has a higher frequency X rays or Infrared

rays?

Pg. 25 in your study guide Pg. 126 in your book

Section 5.1 Assessment #12

Homework