1. The Atomic Structure of Atoms

2. Democritus: Hypothesizing the Atom
Around 460 B.C., Democritus first developed the idea of atoms as the smallest possible bit of matter.
The word “atom” came from the Greek word atomos meaning indivisible
Greek philosophers laid the ground work for the modern atomic theory

3. Dalton: The Atomic Theory
John Dalton, in the early 1800’s, developed the “atomic theory”.
Fun Fact: Dalton was a school teacher and chemist!

4. Dalton’s Atomic Theory:
1. All elements are composed of atoms. Atoms cannot be divided or destroyed.
2. Atoms of the same element are exactly alike. Atoms of different elements are different.
3. The atoms of two or more elements can join together to form compounds.

5. J.J. Thomson:
Discovered the electron.  
He was awarded with the Nobel Prize in Physics in     

6. Lord Ernest Rutherford: 1871-1937
Discovered that most of the atom is made up of "empty space” where the electrons move.
He discovered and named both the nucleus  and protons

7. James Chadwick: 1891-1974 Discovered the neutron
He found neutrons to have essentially the same mass as protons.
He was awarded the Nobel Prize in physics in

8. Niels Bohr: early 1900’s
Discovered electrons traveled in energy levels around the nucleus. 
Bohr’s Model is the one we still use today.

9. REVIEW: Early Atomic Chemists
Democritus
Named the atom
Dalton
Atomic Theory
Thomson
Discovered electron
Rutherford
Named the nucleus, proton, and described the “empty space” where electrons travel
Chadwick
Discovered neutron
Bohr
Discovered electron energy levels

10. Important Information !!
Parts of an Atom
Locations
Nucleus
Electron Cloud
Subatomic Particles
Protons
Neutrons
Electrons

11. Nucleus Is the positively charged, central part of an atom.
Contains protons and neutrons.
Contains almost ALL of the atom’s mass.

12. Inside the Nucleus Protons are positively (+) charged particles.
Neutrons are uncharged particles (Ø); “neutrons are neutral”

13. Outside the Nucleus
Electrons are negatively (-) charged particles located in the electron cloud.
The electron cloud is arranged in energy levels and travels around the atom’s nucleus.

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Electron Cloud
The lowest energy level is closest to the nucleus and holds up to 2 electrons.
Higher energy levels are father from the nucleus and can contain more electrons.
(c) 2007 brainybetty.com All Rights Reserved.

15. Neutral Atoms An atom has an overall neutral charge when:
the # of electrons (-) = the # of protons (+)
Remember, neutrons are neutral!