Opener:

Describe the earliest cell phone you remember.

How have cell phones changed since then?

Why is it important for cell phone developers to know what the older versions were like?

It’s time for…

THE HISTORY OF THE ATOM

Democritus400 B.C.

Proposed that matter is made of about 100 basic kinds of tiny particles he called “atomos” that can’t be divided into smaller particles.

Nobody believed him.

His experiments with gasessuggested that matter wascomposed of tiny particles.

He renewed interest in the idea of atoms.

Antoine Lavosier

1780Known as the Father of

Modern Chemistry

Developed the theory of Conservation of Matter

Antoine

Modern chemistry

John Dalton1803• Atoms are all solid with

uniform density (like a gum ball)

• Atoms are the smallest particles of nature.

• All atoms of the same element are identical.

• All atoms are indivisible• Atoms of different sizes

can combine to make compounds.

An atom, according to

Dalton.

Marie Curie1898

Credited with the discovery of the first radioactive elements.

Theorizes that theses elements emit invisible rays called “radiation”

First person to win Nobel Prizes in TWO different sciences (chemistry and physics).

Discredits part of Dalton’s theory (indivisible atoms)Atoms must have smaller components

Credited for the discovery of the electron, because he realized

the “beam of light” in a Crookes tube was really made of negative

particles.

Realized that electrons were smaller than atoms.

This information discredited part of

Dalton’s atomic theory

Developed the “Plum Pudding” model of the atom

Experimented with magnets

-

Experiment #2

+

Conclusions?• The stream of particles

was …• Negative

Overall, atoms are...

Neutral

Therefore, atoms must also contain charges that are...

Positive

Plum (electrons)

Pudding(positive

stuff)

Today, it would probably be called the “Chocolate Chip Cookie” Model

Max Planck 1900

Developed Quantum Theory.

He discovers that energy is not given off in continuous amounts. Instead, energy is released in small packets that he calls “quanta”.

This idea contradicts our common-sense ideas about energy and matter – but it turns out to be correct!

Energy acts like a particle!

Ernest Rutherford1910

Performed Gold Foil Experiment.

Discovered that atoms had a nucleus!

Disproved “Plum Pudding” model.

Won Nobel Prize for Chemistry.

The Gold Foil Experiment

Bombard thin piece of gold foil with alpha particlesResult: some are deflected while others are unaffectedWhat does it all mean?

Dense, positively charged nucleus.Electrons surround the nucleus like bees around a hive.Atoms are mostly empty space.Problem: Why didn’t electrons get pulled into the nucleus?

Neils Bohr1913• Extended Quantum Theory to

electrons in atoms!• Electrons are in certain orbits at

a specific distance from the nucleus.

• Only certain orbits were “allowed”.

• If an electron stayed in its orbit, it didn’t lose any energy and would not fall into the nucleus.

Atomic Line Spectra

Hydrogen Gas

Prism or diffraction grating

Expected to see a nice progression of color just like

normal BUT…..

Atomic Line Spectra

Gas such as Neon or Hydrogen

Prism or diffraction grating

Instead he got just a few discrete lines of color!

Niels BohrPlanetary Model

• Compares electrons orbiting the nucleus of an atom to planets orbiting around the sun.

• Electrons occupy distinct orbitals.

• Orbitals have certain energies and distances from the nucleus.

• Bohr’s theory explains how light is given off – a huge success!

For Electrons

Nucleus

3 2

2 1

3 1

Heisenberg/SchrodingerQuantum Mechanical Model/

Electron Cloud Model • Regions where electrons are most likely

found are called “electron clouds”.

• Different types of orbitals have different shapes and different levels of energy.

James Chadwick

1932

Established the existence of the neutron.

neutron

1980’s The first atoms

are seen with scanning tunneling microscopes