1. Soon you will be a rocket scientist
Atomic Theory
Soon you will be a rocket scientist

2. Atoms Atoms are composed of particles including: Protons Neutrons
Electrons

3. Nucleus
Contains protons (+) and neutrons

4. Electrons Electrons (-) surround the nucleus in specific energy levels
An equal number of
protons and electrons
means that the atom
is NEUTRAL

5. Atomic Number The number of PROTONS an atom has is its atomic number.
Oxygen has 8 protons in its nucleus. What is its atomic number? 8!

6. Who Developed Atomic Theory?
-early scientists wanted to turn metals such as lead into gold!

7. John Dalton
In the early 1800’s, he started to look at the earth’s atmosphere
He looked at oxygen, carbon dioxide, and nitrogen oxide
He proposed that the tiniest particles were atoms, and these were different in different elements

8. Dalton’s Atomic Theory
1. All matter is made of small particles called atoms
2. Atoms cannot be created, destroyed, or divided into smaller pieces
3. All atoms of the same element are identical in mass and size
4. Compounds are created when atoms of different elements link together

10. J. J. Thomson
He studied electric currents and discovered that currents were streams of negatively charged particles
He reasoned that all atoms must contain these negative particles
No one believed that there were smaller particles than an atom!

11. Ernest Rutherford
He discovered the nucleus-the tiny, dense, POSITIVELY charged centre of the atom
He also proposed that there were two kinds of particles inside the nucleus, protons and neutrons

12. Neils Bohr
In the early 1900’s, he studied the electrons surrounding the nucleus
He proposed that electrons surround the nucleus in specific energy “levels”.
This meant that each electron has a specific amount of energy.

13. Subatomic Particles
NAME
Symbol
Relative Mass
Electric Charge
Location in the Atom
PROTON p
1836 +
Nucleus
NEUTRON n
1837
ELECTRON e 1 -
Surrounding

14. Final Notes Remember that the nucleus is always positive!
The number of protons in the nucleus is the atomic number
Electrons take up most of the volume of an atom, even though they weigh the least!