History of the Atom

1. History of the Atom http://lifesciencereality.files.wordpress.com/2008/06/atom.jpg What is an atom? Who discovered the atom?

2. What is an Atom? • An atom is the smallest particle into which an element can be divided • An atom consists of 3 parts: • Protons • Neutrons • Electrons

3. Inside an Atom Inside the atom is the nucleus • The nucleus is the tiny, central core of an atom. (How tiny?) • Inside the nucleus are protons and neutrons • Protons- have a positive charge (+) • Neutrons- have a neutral charge (0) http://www.csmate.colostate.edu/cltw/cohortpages/viney/atom.jpg

4. Inside an Atom Orbiting around the outside of the nucleus are electrons: • Move rapidly in all directions of the nucleus • Have a negative charge

5. Inside an Atom Orbiting around the outside of the nucleus are electrons • Electrons • Move rapidly in all directions of the nucleus • Have a negative charge

6. Who Discovered Atoms? Democritus 440 BCE • Summary of Model/Idea • Democritus thought that if you cut something in half over and over, eventually you would end up with a particle that could not be cut (Atom) • Description of Model: • He thought atoms were small, hard particles. • He thought that atoms were made of a single material formed into different shapes and sizes.

7. Who Discovered Atoms? John Dalton Late 1700s Summary of Model/idea: • All substances are made of atoms. Atoms are small particles that cannot be created, divided, or destroyed. • Atoms of the same element are exactly alike, and atoms of different elements are different. • Atoms join together with other atoms to make new substances. Description of model: invisible, indestructible, solid sphere like a billiard ball

8. Who Discovered Atoms? J.J. Thomson 1897 • Summary of Model/idea: • Discovered there were small particles inside the atom which meant it could be divided up even smaller. • Discovered the existence of electrons by using a cathode-ray tube and proposed the Plum Pudding model. • Description of Model: • “Plum Pudding” model: stated that electrons were mixed throughout an atom, like plums in pudding.

9. http://www.epa.gov/radiation/images/ruthbohr.jpg Who Discovered Atoms? Ernest Rutherford 1909 • Summary of Model/idea: • Tested the Thompson’s theory by aiming a beam of small, positively charged particles at a thin sheet of gold foil that had a special coating behind it. • He discovered that atoms are mostly empty space • Discovered the nucleus with positive charged particles • Description of Model • Atoms are mostly empty space • Positive center (nucleus) with electrons circling the center

10. Who Discovered Atoms? Neils Bohr 1913 • Summary of Model/idea: • Studied the way atoms react to light, which lead him to believe that electrons move around certain paths, or energy levels. • Believed that electrons could jump from a path on one level to a path on another level (like steps on a ladder) • Description of model: • Electrons circle the nucleus in different orbits, like the planets around the sun http://www.tpub.com/content/doe/h1019v1/img/h1019v1_27_5.jpg

11. Who Discovered Atoms? James Chadwick 1932 • Discovered the Neutron • Used the work of Rutherford to determine that the neutron did exist.

12. Modern Atomic Theory Modern Model • Summary and description of model: • Based on the Bohr Model • Nucleus found in center of atom. Protons and neutrons are inside. • Electrons do not travel in definite paths like Bohr thought. Their paths cannot be predicted. • Electrons are found in regions called electron clouds. http://wiki.one-school.net/images/thumb/d/d4/ChadwicksModel.png/400px-ChadwicksModel.png