The History of the Atom From Democritus to Today’s Modern Theory
Democritus • 400 BC • Proposed that all matter is made up of atoms. • Thought atoms were small, hard particles of different shapes and sizes. • Coined the term ‘Atom’ • From the Greek word meaning ‘Can not be divided.’
Alchemists • First ‘Chemists’ around 900 AD • First to include observation and experimentation with pure thought methods of science.
Lavoisier • 1785 • Authored the Law of Conservation of Mass • Did experiments to prove that matter does not disappear during a chemical reaction. • ‘Matter can not be created or destroyed, it can only be rearranged.’
Dalton • Father of Modern Atomic Theory • 1800’s • All matter consists of atoms with space in between. • Atoms of the same kind of element are identical to each other. • There are as many different kinds of atoms as there are different elements. • Atoms are solid spheres. • ‘Billiard Ball Model’
Thomson • 1904 • Inferred that atoms contain small negatively charged particles. • He called them ‘electrons.’ • He thought the electrons were dispersed throughout a positively charged sphere. • ‘Chocolate Chip Cookie Dough Model’
Rutherford • 1911 • Famous Gold Foil Experiment • Discovered and named the ‘nucleus’ of the atom. • Proposed that most of the mass and all of the positive charges of an atom are in its nucleus. • ‘Peach Pit Model’
Bohr • 1913 • Concluded that electrons travel in fixed orbits around the nucleus based on the amount of energy they contain. • He called the ‘orbits’ Energy Levels. • ‘Solar System Model’
Schrodinger and Heisenburg • 1926 • Scientists described the electron region of the atom as a cloud around the nucleus. • This cloud area shows that electrons do not orbit the nucleus in definite paths, but are likely to be in a given region at any particular time. • ‘Modern Electron Cloud Model’
Chadwick • 1932 • Worked with E. Rutherford in the discovery of a third sub-atomic particle. • He concluded this particle to be free of electrical charge and he called it the ‘neutron.’ • Concluded it was located in the nucleus along with the protons.
Quarks and Leptons • Particles within particles. • Protons and Neutrons are made of Quarks: Up Down Strange Top Charm Bottom • Electrons are a small thin type of Lepton.