ATOMIC STRUCTURE

WHAT IS AN ATOM? The smallest part of an element that keeps all of that element’s chemical and physical properties

DEMOCRITUS--_Greek philosopher; first to use the word atom to describe smallest pieces of matter; called the smallest part of matter “atomos” which meant indivisible.

DALTON— English chemist ; first to publish the atomic theory which had 5 basic statements:

1. All matter is made up of indivisible atoms.

2.Atoms of the same element are identical. 3.Atoms of different elements are different. 4.Atoms are not created or destroyed in a

chemical reaction. 5.Atoms chemically join to form molecules

(compounds.)

THOMSON—first to actually develop a model of the atom by using indirect evidence ; His model is known as the “Plum Pudding Model”; also given credit for discovering the electron; said that the # of protons must equal the # of electrons.

RUTHERFORD—discovered that the atom has a very small, dense, positively charged center called the nucleus ; his experiment was called the “Gold Foil Experiment” .

  ****see p. 74—75 (KNOW HOW HIS

RESULTS ALLOWED HIM TO REASON THAT THE ATOM HAS A NUCLEUS IN THE CENTER!!)

 

CHADWICK—discovered neutrons which have neutral (no) charge and are located in the atom’s nucleus

BOHR—said that electrons occupy fixed, definite energy levels within the atom’s electron cloud ; electrons with the most energy are farther away from the nucleus.

MODERN WAVE MODEL—electrons are located only in highly likely or highly probable locations because they are continuously moving due to the losing and gaining of energy.

  1st energy level = maximum of 2

electrons 2nd energy level = maximum of 8

electrons 3rd energy level = maximum of 8 or 18

electrons

*********ALL MODELS OF THE ATOM ARE BASED UPON INDIRECT EVIDENCE.

  ******2 MAIN PARTS OF THE ATOM:

NUCLEUS & ELECTRON CLOUD.