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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.’.
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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.
