The Atomic Theory l Democritus l 440 BCE

The Atomic Theory

l Democritus l 440 BCE Ø Believed § proposed the atom all matter was made of atoms called this particle the atom (atomos which means not able to divide).

The Father of the Atomic Theory l l John Dalton viewed the atom as a solid ball. Proposed in 1803 Ø Ø Ø 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 l J. J. Thomson proposed the Plum-Pudding Model (named after is favorite dessert) l l 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 l Ernest Rutherford discovered the atom was made of mostly empty space with a dense, positively charged center surrounded by electrons-1909 l Called this center the nucleus and the positive particles in the nucleus he called protons. l Former student of J. J. Thomson

Improving the Modern Theory l Niels Bohr suggested electrons move in distinct, circular patterns known as energy levels - 1913 l l 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 l Schrödinger and Heisenberg: found that eˉ did not have a definite path but. . -1926 l Are unpredictable and found in a region called the electron cloud surrounding the nucleus www. csmate. colostate. ed

Finding the Neutron l 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 l He called this particle the neutron.