The Atomic Theory
Democritus proposed the atom 440 BCE Believed all matter was made of atoms called this particle the atom (atomos which means not able to divide).
The Father of the Atomic Theory John Dalton viewed the atom as a solid ball. Proposed in 1803 All things are made of atoms and cannot be divided Atoms of same element are alike and atoms of different elements are different Atoms can join with others to make new things
Improving the Modern Theory J.J. Thomson proposed the Plum-Pudding Model (named after is favorite dessert) the atom has positively and negatively charged particles evenly distributed throughout the atom discovered the electrons in 1897 www.csmate.colostate.edu
Improving the Modern Theory Ernest Rutherford discovered the atom was made of mostly empty space with a dense, positively charged center surrounded by electrons-1909 Called this center the nucleus and the positive particles in the nucleus he called protons. Former student of J.J. Thomson
Improving the Modern Theory Niels Bohr suggested electrons move in distinct, circular patterns known as energy levels - 1913 eˉ could jump from one energy level to another but not in between Model known as Bohr’s Model http://education.jlab.org/qa/atom_model_03.gif
More Improvements Schrödinger and Heisenberg: found that eˉ did not have a definite path but.. -1926 Are unpredictable and found in a region called the electron cloud surrounding the nucleus www.csmate.colostate.ed
Finding the Neutron James Chadwick discovered that the center of the atom contained another particle that carried no charge and had a mass close to a proton -1932 He called this particle the neutron.