• Atomic History
• ``WKRP`` atom video
• Bohr Rutherford Diagrams
• Page 16 Numbers 1-10

• A Model is a human construct to help us better understand real world systems.
• A Theory is an explanation of the natural world that can incorporate laws, hypotheses and facts.
– It is testable, and can be refined or rejected.
• A model is used to explain a theory

Empedocles: Greece 450 B.C.
• Earth, Fire, Water, Air
• Everything is made up of these four elements
• Different types of matter are combinations of these basic elements
• Based on philosophy, not experiment
• Model accepted for 2000 years.

• Matter is made of tiny indivisible particles called atoms
• Different elements are made of different atoms
• All matter is made up of atoms and empty space

• All matter is made of atoms too small to see.
• Each element has its own kind of atom with characteristic properties
• Compounds created when atoms of different elements link to form molecules
• Atoms cannot be created or destroyed in a chemical reaction

• Discovered evidence of particles within the atom
• Atoms contain negatively charged particles called electrons
• Thought electrons were embedded in a positive sphere
• Resulting atoms are neutral or uncharged

• Discovered evidence of particles within the atom
• Atoms contain negatively charged particles called electrons
• Thought electrons were embedded in a positive sphere
• Resulting atoms are neutral or uncharged

Rutherford: New Zealand 1911
Canada (McGill)
• Positive centre called the nucleus
• Protons positively charged particles in the nucleus
• Surrounded by mostly empty space containing rapidly moving negative electrons
• At 5’9”, my nearest e- would be 10 km away!

• Used a thin film of gold foil to prove that matter was mostly empty space
• The electron should have gone straight through…
• Some bounced back!
• Matter was mostly empty space
• Core had a tiny dense mass called the nucleus

There was a problem with
Rutherford`s Model:
• If opposites attract, why do the electrons not fly into the nucleus!?

• Electrons orbit the nucleus in shells
• Only a certain number of electrons can be in each shell
• Orbits represent different energy levels of electrons
• BUT: electrons cannot exist between energy levels.
• What happens?

• Light can have particle properties, and is a form of energy
• Maybe electron particles can have energy properties
• Electrons cannot exist between energy levels
• They only “jump” them, and get or give off energy.

Chadwick: England 1932
• James Chadwick`s experiments suggested the existence of neutrons
• Neutrons have no charge
• Found in the nucleus
• Have the same mass as protons

• Elements are symbolized with their mass number (A) and atomic number (Z)
• A - Z = # of neutrons
• Calculate # of electrons, neutrons and protons for
Ar, Ca, Br

Atomic
Number
Mass
Number
Protons Neutrons Electrons
Br 35 80 35 45 35
Ar 18 40 18 22 18
Ca 20 40 20 20 20

Plank, Schrodinger, Heisenberg: 1926
• Electrons create standing waves
• Orbitals can be described as electron density clouds
• The densest area of a cloud is where there is greatest probability of finding electrons