1. History of the atom
UNIT 2

2. In the beginning… People believed:
All matter can be divided into smaller parts without limits (there was no end)

3. Aristotle 384-322 BC A Greek philosopher, not a scientist
Stated that all matter is composed of one substance, “hyle” (we are still not sure what hyle is)
This statement was accepted until the 1600’s

4. Democritus 400 BC First person to adopt an atomic theory
Stated everything was made of empty space and “atoms”
Atoms – invisible particles

5. Dalton
John Dalton
1766 – 1844
Considered the father of atomic theory and chemistry
His law was called DALTON’S ATOMIC THEORY

6. Dalton’s Atomic Theory
An element is made of atoms
Atoms of an element are all alike
Atoms can’t be created or destroyed
Atoms of elements combine to form molecules and compound
Atoms combine, separate, and rearrange in chemical reactions

7. Modern Atomic Theory
Dalton’s theory has been modified into the modern atomic theory which we use today
Only one exception to Dalton’s theory – atoms under special conditions may be divided. In other words, an atom can be fused apart into the particle which make up an atom (electrons, neutrons, and protons)

8. The Periodic Table Use this and your periodic table to answer the questions about the elements
Atomic number
Atomic Mass 8 O
Symbol
Oxygen
Name

9. Isotope
Definition –
An atom with the same number of protons but different number of neutrons
The mass of an element is an average, due to the amount of isotopes that occur in nature
Click on the link below then on the element listed and count the number of isotopes (just count the red symbols listed under isotopes)

10. THE ATOM
AND ITS PARTS

11. The diagram of the atom
Electrons + -
Protons
Neutrons
Nucleus

12. THE NUCLEUS The center of the atom
Protons and neutrons reside in the nucleus
The mass of the element comes from the nucleus

13. THE PROTON Symbol - p+ Discovered by E. Rutherford
It has a positive charge
which balances out the electron’s negative charge
resides in the nucleus in the center of the atom
It is the same as the atomic number on the periodic table – This is the number that makes the element what it is.

14. THE NEUTRON Symbol - n0 Discoverer - J Chadwick Has no charge
The neutron also resides in the nucleus
To calculate the neutron:
Atomic mass rounded - # of protons

15. Electrons are the same as protons
THE ELECTRON
Symbol - e-
Discover - JJ Thomson
Has a negative charge
The electron is like a hyperactive two year old, it moves very fast and circles the nucleus
Electrons are the same as protons

16. Diagramming Elements
Using your periodic table, the notes you just took, and your brain – fill in the chart