1. Defining the Atom Structure of the Nuclear Atom
Atomic Structure
Defining the Atom
Structure of the Nuclear Atom

2. I CAN identify and describe the particles that form an atom.

3. Defining the Atom EARLY MODELS OF THE ATOM
An ATOM is the SMALLEST PARTICLE of an ELEMENT that RETAINS its identity in a CHEMICAL REACTION.
The Greek philosopher DEMOCRITUS was one of the first people to suggest the existence of the ATOM.
Democritus described atoms as INDIVISIBLE and INDESTRUCTIBLE.

4. Early ideas of the atom DID NOT CATCH ON because the philosophers COULD NOT TEST their ideas.
More than 2000 YEARS passed before the idea of the atom became an accepted reality.
JOHN DALTON, an English teacher/chemist, used EXPERIMENTAL methods to test DEMOCRITUS’
ideas about the atom.

5. Dalton’s Atomic Theory
Dalton formulated FOUR STATEMENTS that formed the basis of the modern idea of the atom:
All ELEMENTS are composed of ATOMS.
ATOMS of the SAME element are IDENTICAL.
ATOMS can COMBINE CHEMCIALLY to form COMPOUNDS.
ATOMS keep their IDENTITY during CHEMICAL REACTIONS.

6. Sizing Up the Atom Atoms are EXTREMELY SMALL! 7.0 x 109 people.
A COPPER PENNY contains approximately x 1022 atoms of copper.
The population of the Earth is approximately
7.0 x 109 people.
THEREFORE there is about 4,000,000,000, [4 TRILLION] times more ATOMS IN A COPPER PENNY than there are people on the Earth!

7. STRUCTURE OF THE NUCLEAR ATOM
SUBATOMIC PARTICLES
Atoms are composed of THREE BASIC PARTICLE known as SUBATOMIC PARTICLES.
ELECTRONS were first discover in 1897.
Electrons have a NEGATIVE electrical charge.
Electrons have a VERY SMALL MASS. It takes 1837 electrons to weigh as much as ONE PROTON. 
The symbol for an electron is e- [note it’s lower case!]

8. PROTONS were first discovered in 1886.
Protons have a POSITIVE electrical charge.
Protons have a mass about 1837 times larger than ELECTRONS.
The symbol for a proton is P+ [note the P is upper case!]

9. NEUTRONS were discovered in 1932.
Neutrons have NO ELECTRICAL CHARGE (they are NEUTRAL)!
Neutrons have a mass ONLY SLIGHTLY GREATER THAN a proton.
The symbol for neutron is N0 [note it is upper case!]

10. THE NUCLEUS AND ELECTRON CLOUD
PROTONS and NEUTORNS are found in the NUCLEUS of the atom.
The nucleus is the SMALL, DENSE and SOLID central core of the atom.
More than 99.9% of the mass of an atom is located in the NUCLEUS.
The atom’s ELECTRONS are found in an area SURROUNDING THE NUCLEUS known as the ELECTRON CLOUD.
The electron cloud can be compared to BEES SWARMING AROUND A HIVE and it mostly just an area of EMPTY SPACE where as the nucleus is a SOLID structure.

11. Atom Models Over Time
Over the years, the idea of what an atom looks like has changed a great deal.
In the space below, sketch a drawing of each atom model. Go to and find each of these models of the atom.
Democritus/Dalton Model
Thomson Model
Rutherford Model
Bohr Model
Quantum Cloud Model