1. Atomic Theory and Atomic Structure
Courtesy of Mrs. Danza
Ch. 4 Intro to Matter Text

2. Democritus 440 BC Greek Philosopher
Universe was made of empty space and tiny bits of stuff
Called these tiny bits of stuff “atomos”
If you keep cutting something in half, eventually you would end up with a particle that could not be cut.
Atom- “not able to be divided”

3. Aristotle Greek Philosopher
Matter is made of particles, which we call atoms.
An atom is the smallest particle into which an element can be divided and still be the same substance.

4. John Dalton Late 1700’s- British Chemist and Teacher
Published in 1803:
All substances are made of atoms. Atoms are small particles that cannot be divided, created, or destroyed.
Atoms of the same element are exactly alike, and atom of different elements are different.
Atoms join with other atoms to make new substances.

5. J.J. Thomson 1897- British Scientist
There are small particles inside the atom.
Created the “plum-pudding” model. (Looks like chocolate chip ice cream)
Atom made of a positively charged material with the negatively charged electrons scattered through it.

6. Ernest Rutherford 1909- A Student of Thomson
“Gold Foil” Experiment
Atoms are made of mostly empty space.
A tiny part of an atom is made of dense matter.
1911- Revised Theory- New Model
The center of the atom, the nucleus, is extremely dense and has a positive charge.

7. Niels Bohr 1913- Danish Scientist
Electrons move around the nucleus in paths or energy levels.

8. Erwin Schrodinger (Austrian Physicist) and Werner Heisenberg (German Physicist)
Electrons do NOT travel in specific paths.
They travel in Electron Clouds (a region around the nucleus where electrons are found)

9. What is an atom made of?

10. What are Protons? Much larger and heavier than electrons
Protons have a positive charge (+)
Located in the nucleus of the atom 
Atomic Mass Unit (amu)- SI Unit used to express the mass of parts of atoms
1 proton = 1 amu

11. What are Neutrons? Large and ______ like protons
Neutrons have __________
Located in the nucleus of the atom
Mass of one neutron = ________
Mass of proton is __________ to the mass of a neutron

12. What are Electrons? Tiny, very light particles
Have a negative electrical charge (-)
Move around the outside of the nucleus
Mass is almost 0 amu
Electron mass is so low, it is often not even considered when recording the mass of the whole atom

13. How do we describe atoms?
Atomic Number equals the number of protons in the nucleus.
In a neutral atom, the number of protons equals the number of electrons.
Atomic Mass Number is equal to the number of protons plus neutrons.

14. What are Ions?
An atom that carries an electrical charge is called an ion
If the atom loses electrons, the atom becomes positively charged (because the number of positively charged protons will be more the number of electrons)
If an atom gains electrons, the atom becomes negatively charged (more negative charges than positive charges)

15. What are Ions? The number of protons does not change in an ion
The number of neutrons does not change in an ions
So, both the atomic number and the atomic mass remain the same.

16. What are Isotopes?
An atom that has the same number of protons (atomic number) as other atoms in the same element BUT a DIFFERENT amount of neutrons; therefore, it has different atomic masses.
Some are unstable- the nucleus will change over time, losing neutrons until it becomes stable
Some are considered Radioactive- as the nucleus loses neutrons, it gives off high energy light particles
Identify Isotopes by mass number. (Sum of the protons and neutrons.)

17. What are Isotopes?

18. What holds atoms together?
Gravitational Force- mass attraction
Electromagnetic Force- charge attraction
Strong Force- keeps the nucleus together
Weak Force- Radioactive Atoms Only.