The History Of

Front 1

Atoms

Back 1

smallest unit of an elements that maintains the properties of the element

Front 2

Elements

Back 2

pure substance made up of one type of atom

Front 3

Compounds

Back 3

substances made from atoms of two or more elements that are chemically bonded

Front 4

400 B.C. – Democritus Theory

Back 4

400 B.C. – Democritus theorized that atoms were specific to the material that they made up
Ex: Atoms of stone were unique to stone and different from the atoms of other materials, such as fur
Theory was rejected by many including Aristotle and Plato

Front 5

350 B.C. – Aristotle Theory

Back 5

350 B.C. – Aristotle believe that all matter was made from 4 “elements”
Earth, Fire, Water, and Air
Theory was wrong – but believed for 2000 years

Front 6

Dalton’s Atomic Theory

Back 6

All matter is composed of atoms.
Atoms of an element are identical.
Each element has different atoms.
Atoms cannot be subdivided, created, or destroyed.
Atoms of different elements combine in simple whole-number ratios to form compounds.
In chemical reactions, atoms are combined, separated, or rearranged.

Front 7

Describe the discovery of the electron

Back 7

1897: Discovery of the Electron
J.J. Thomson’s Cathode Ray Tube Experiment
Through voltage fluorescent streams of electricity travel from the bottom part of a glass tube to the top. 
These mysterious rays are streams of particles much smaller than atoms, they are in fact minuscule pieces of atoms that make up all of the matter in atoms.
The rays actually were made up of electrons: very small, negatively charged particles

Front 8

Describe the J.J. Thomson’s Atom

Back 8

Called the plum pudding model because it looked like pudding with plums in it!

Front 9

Gold Foil Experiment - Atomic Level

Back 9

Rutherford reasoned that each atom in the gold foil contained a small, dense, positively charged nucleus surrounded by electrons. A small number of the alpha particles directed toward the foil were deflected by the tiny nucleus. Most of the particles passed through undisturbed.

Front 10

1913: Bohr’s Atomic Model

Back 10

Niels Bohr believe the electrons were on fixed paths called ENERGY LEVELS as they travel around the nucleus of the atom

Front 11

1932: Discovering of the Neutron

Back 11

Hardest to discover because it is neutral in charge
Discovered by James Chadwick (Rutherford’s assistant)
Masses of atoms didn’t match up = missing particle in the atom
Particle must be neutral because protons & electrons already discovered

Front 12

Modern Atomic Theory

Back 12

Some important concepts remain unchanged:
All matter is composed of atoms.
3. Atoms of any one element differ in properties from atoms of another element.
5. Atoms of different elements combine in simple whole-number ratios to form compounds.
6. In chemical reactions, atoms are combined, separated, or rearranged.

Front 13

What are atoms divisible into (smaller particles)?

Back 13

protons, electrons, and neutrons

Front 14

How can a given element have atoms with different masses?

Back 14

by changing the number of neutrons

Front 15

Where are electrons found in atoms?

Back 15

Electrons are found in electrons clouds, which surround the nucleus (Not on fixed paths orbiting the nucleus)