Warm-Up• What is the symbol for the following elements.

• Gold• Au

• Aluminum• Al

• Sodium• Na

• Lithium• Li

3-1 – Atomic Theories• Objectives

• Describe the four main models of the atom and explain how each was discovered.

Greek Model of Atoms• 400 B.C. Greek

philosopher Democritus

• “atomos” which means, indivisible.

• Atoms are hard, solid particles

• same material • different shapes and

sizes.

Greek Model (cont.)• Aristotle disagreed with

Democritus.• Aristotle said there was no

limit to division of matter.• Aristotle thought matter

consisted of four types.• Fire, Earth, Water, Air

Dalton’s Atomic Theory• 1803 – John Dalton, English Chemist• All elements are composed of atoms.• All atoms of the same element = mass• Compounds contains atoms of more

than one element.• In a compound, atoms of different

elements always combine in the same way• H2O• Na2CO3

Thomson’s Model• 1897 – J.J. Thomson, English

Chemist.• Atoms are made of even smaller

particles.• Plum pudding model• Positively charged “pudding”

through which negative particles are scattered.

• Atoms are neutral, therefore, there must be + particles too, but Thomson never found them.

Thompson’s Experiment

Rutherford’s Atomic Model• 1911 – Ernest Rutherford,

British physicist• Gold Foil experiment.• Atom has a small, dense

positively charged center called the Nucleus.

• Negative electrons are scattered outside the nucleus.

• If an atom was the size of a baseball stadium, the nucleus would be the size of a marble.

Rutherford’s Experiment• A beam of + particles (alpha particles) shot through a

thin sheet of gold foil.• Most particles passed straight through. (Most of atom is

empty space.)• A few were deflected. (Positive core-similar charges

repel each other.)• Very few bounced off. (Solid core is very small.)

Actual Results.Actual Results.Results of foil experiment if Results of foil experiment if Plum Pudding model had been Plum Pudding model had been correct.correct.

Three Way to Remember the Models• Dogs Sort Socks = Dalton’s Solid Sphere• Turtles Play Ping-pong = Thomson’s Plum Pudding

• Rats Play Nintendo = Rutherford’s Positive Nucleus

3-1 Summary• Who founded atomic theory?

• Ancient Greeks founded atomic theory.• Thought matter was made up of four elements• Democritus believed all matter was made up of

atoms.• Who founded modern atomic theory?

• John Dalton, father of modern atomic theory.• Developed atom theory; Solid sphere• Element have same make up• Compounds always combine the same way.

3-1 Summary (Cont.)• Thomson Atomic Theory

• Experiment with Cathode ray tubes.• Atoms are made up of smaller particles.• Plum Pudding model

• Rutherford Atomic Theory• Gold foil experiment• Discovered the nucleus• Positive nucleus

Warm Up• Oops!! Those “harmless” Germanium capsules

you just swallowed may have an extra proton in each nucleus.

Is this good news or bad news? Why?

This is bad news, for germanium nucleus with an additional proton is not Germanium, but arsenic!!!!