ATOMIC STRUCTURE

ATOMS ¢ Basic building block for everything in the universe ¢ Smallest unit of matter ¢ Too small to see in a microscope ¢ Held together by attraction forces (positive attracted to

negative charge) Just how small is an atom?

STRUCTURE

¢ Three basic parts of an atom: 1.  Electrons 2.  Protons 3.  Neutrons

PROTONS

¢ Have a positive charge ¢ Are found in the nucleus of the atom

NEUTRONS

¢ Have a neutral (no) charge ¢ Found in the nucleus of the atom

ELECTRONS ¢ Smallest of the three particles of an atom ¢ Found in “shells” or orbitals that surround the nucleus

of an atom ¢ Have a negative charge

HOW DO WE KNOW??

¢ How do we know what atoms look like?

PLUM PUDDING ATOM

¢  J.J. Thomson ¢ Each atom was a sphere

�  Filled with a positively charged fluid, known as “pudding”

�  Scattered in this fluid were negatively charged electrons, and these were the “plums” in the pudding

�  Thought the positive fluid held the electrons in the atom due to electric forces

PLUM PUDDING ATOM

WHY IS IT INCORRECT?

¢ Ernest Rutherford performed the Gold Foil Experiment �  Shot a beam of alpha particles at a sheet of gold foil �  If the “plum pudding” model was correct, all of the

alpha particles should have passed through �  Some were deflected back….WHY?

¢  Hit the tiny, dense nucleus in the center of the atom!

BOHR MODEL

¢ Central nucleus �  Protons �  Neutrons

¢ Electrons orbit the nucleus �  Just like planets orbit the sun �  Can “jump” between orbits when the atom gains or

loses energy

A BOY AND HIS ATOM

The World's Smallest Movie