1. Is this really what it looks like?
Atomic Theory
Is this really what it looks like?

2. What is an Atom? It is the most basic unit of matter.
Remember- matter is anything that has volume and takes up space.
All matter can be simplified down to 1 of 118 elements.

3. Atomic Theory and Cakes
Cakes are like all of matter.
The ingredients of cake are like the elements.
An ingredient split down to its smallest piece is like an atom.

4. What is an Atom?
The appearance of an atom has changed many times as new discoveries have been made.
Scientists now have a clear picture of an atom.

5. Atomic History Aristotle vs. Democritus (400 b.c.)
Aristotle believed everything could be broken down into one of four things: earth, water, fire, and air.
Democritus believed all things are made of small indivisible particles called “atoms”
Since Aristotle was a “bigger” scientist his idea was accepted and the concept of an atom was forgotten for about 2000 years.

6. Dalton's Atomic Theory (1805)
1. All matter consists of atoms, tiny indivisible particles of an element that cannot be created or destroyed. 2. Atoms of one element cannot be converted into atoms of another element. 3. Atoms of an element are identical in mass and other properties and are different from atoms of any other element. 4. Compounds result from the chemical combination of a specific ratio of atoms of different elements.

7. Dalton’s Atom Dalton believed atoms where like “little round balls.”
Flaws in Dalton’s Theory.
Atoms can be subdivided
Not all atoms of an element are identical in mass.

8. Thomson Model (1897)
Discovered the electron; and it was negatively charged.
To balance the charge of the electron the atom must contain a positive core.

9. Thomson’s Atom
Sometimes called the plum pudding atom.

10. Nagaoka Contribution (1904)
Proposed the idea that electrons orbited around a positive “core”, called nucleus. Much the same way planets orbit around the sun.

11. Rutherford Model (1911)
He shot the nucleus of an atom at a sheet of gold foil. Instead of seeing the nucleus’s bounce off at an angle, most of them passed straight though!

12. Rutherford’ Model
An atom is mostly composed of empty space !

13. Bohr Model (1913)
Proposed that electrons moved in specific regions, called “shells” . Electrons give off or absorb energy as they move between shells.
Much the way an onion has layers. Atoms have layers.

14. Bohr Model
Each layer had a specific number of electrons it could hold.

15. Chadwick Contribution.
An atom often weighed more than it was predicted too. Chadwick proposed and found that some atoms contain another particle called a neutron.
Neutrons are neither positive or negative and are found in the nucleus.

16. Modern Atomic Theory.
The modern atomic theory is a mixture of all the work that happened around the 1920’s
The study of the atom and how it works is called Quantum Mechanics.

17. Summary of Atomic Theory.
The atom is composed protons, which are positively charged and located in the nucleus.
The nucleus is surrounded by negatively charged electrons, which are located in specific “shells”
The nucleus can also contain a neutron, which has no charge.

18. What determines an Element?
The atoms of one element are different from the atoms of another element.
An element can be determined by the number of protons in the nucleus of its atom.

19. Atomic Number
Atoms of the same element have the same number of protons in the nucleus.
The number of protons an atom contains determines which element it is.
Ex. Hydrogen contains 1 proton, thus all hydrogen’s have only 1 proton in its nucleus.

20. Homework
Read over your notes and make sure they are clear to you.