The Greeks History of the Atom Not the history of atom, but the idea of the atom In 400 B.C the Greeks tried to understand matter (chemicals) and broke them down into earth, wind, fire, and air. Democritus and Leucippus Greek philosophers
460 BC Democritus develops the idea of atoms he pounded up materials in his pestle and mortar until he had reduced them to smaller and smaller particles which he called ATOMA (greek for indivisible) No experiments to support idea Continuous vs. discontinuous theory of matter Democritus’s model of atom No protons, electrons, or neutrons Solid and INDESTRUCTABLE
Four Element Theory Plato was an atomist Thought all matter was composed of 4 elements: –Earth (cool, heavy) –Water (wet) –Fire (hot) –Air (light) –Ether (close to heaven) ‘MATTER’ FIRE EARTHAIR WATER Hot Wet Cold Dry Relation of the four elements and the four qualities Blend these “elements” in different proportions to get all substances
Anaxagoras Anaxagoras (Greek, born 500 B.C.) seeds –Suggested every substance had its own kind of “seeds” that clustered together to make the substance, much as our atoms cluster to make molecules. Some Early Ideas on Matter O’Connor Davis, MacNab, McClellan, CHEMISTRY Experiments and Principles 1982, page 26, Empedocles Empedocles (Greek, born in Sicily, 490 B.C.) – earth, air, fire, and water –Suggested there were only four basic seeds – earth, air, fire, and water. The elementary substances (atoms to us) combined in various ways to make everything. Democritus (Thracian, born 470 B.C.) proposed the word atom –Actually proposed the word atom (indivisible) because he believed that all matter consisted of such tiny units with voids between, an idea quite similar to our own beliefs. It was rejected by Aristotle and thus lost for 2000 years. Aristotle Aristotle (Greek, born 384 B.C.) – heat, cold, dryness, moisture – as basic elements –Added the idea of “qualities” – heat, cold, dryness, moisture – as basic elements which combined as shown in the diagram (previous page). Hot + dry made fire; hot + wet made air, and so on. Some Ancient Thoughts About Matter: Democritus and Aristotle. (02:03)Some Ancient Thoughts About Matter: Democritus and Aristotle. Video Segment 1 of 6 from the Full Video
Who Was Right? Greek society was slave based Beneath famous to work with hands did not experiment Greeks settled disagreements by argument Aristotle was more famous He won! His ideas carried through middle ages. Alchemists change lead to gold California WEB
Alchemy After that chemistry was ruled by alchemy. They believed that that could take any cheap metals and turn them into gold. Alchemists were almost like magicians. –elixirs, physical immortality
Contributions of alchemists: Information about elements - the elements mercury, sulfur, and antimony were discovered - properties of some elements Develop lab apparatus / procedures / experimental techniques - alchemists learned how to prepare acids. - developed several alloys - new glassware
HISTORY OF THE ATOM 1808 John Dalton suggested that all matter was made up of tiny spheres that were able to bounce around with perfect elasticity and called them ATOMS
“POP QUIZ”! Define the following terms on a separate sheet of paper –Atomic number –Ion –Molecule –Atom –Kernel Electrons
How’d You Do? The number of protons in the nucleus of an atom of an element An atom or group of atoms that has a positive or negative charge due to a gain or loss of electrons A neutral chemically bonded group of atoms that act as a unit The smallest particle of an element that retains the properties of that element An electron that is not considered to be part of the valence shell
HISTORY OF THE ATOM 1898 Joseph John Thompson found that atoms could sometimes eject a far smaller negative particle which he called an ELECTRON
HISTORY OF THE ATOM Thompson develops the idea that an atom was made up of electrons scattered unevenly within an elastic sphere surrounded by a soup of positive charge to balance the electron's charge 1904 like plums surrounded by pudding. PLUM PUDDING MODEL
HISTORY OF THE ATOM 1910 Ernest Rutherford oversaw Geiger and Marsden carrying out his famous experiment. they fired Helium nuclei at a piece of gold foil which was only a few atoms thick. they found that although most of them passed through. About 1 in 10,000 hit Ernest Rutherford's Experiment.Ernest Rutherford's Experiment. (00:59) Video Segment 2 of 6 from the Full Video Matter and Energy: Matter: What Is It? 09/20/07 6 - 8 The Structure and Scale of the Atom. (02:46) Matter and Energy: Matter: What Is It? The Structure and Scale of the Atom. Video Segment 3 of 6 from the Full Video
HISTORY OF THE ATOM gold foil helium nuclei They found that while most of the helium nuclei passed through the foil, a small number were deflected and, to their surprise, some helium nuclei bounced straight back. helium nuclei
HISTORY OF THE ATOM Rutherford’s new evidence allowed him to propose a more detailed model with a central nucleus. He suggested that the positive charge was all in a central nucleus. With this holding the electrons in place by electrical attraction However, this was not the end of the story.
HISTORY OF THE ATOM 1913 Niels Bohr studied under Rutherford at the Victoria University in Manchester. Bohr refined Rutherford's idea by adding that the electrons were in orbits. Rather like planets orbiting the sun. With each orbit only able to contain a set number of electrons.
HELIUM ATOM + N N + - - proton electron neutron Shell What do these particles consist of?
Timeline 20001000300 AD American Independence (1776) Issac Newton (1642 - 1727) 400 BC Greeks (Democratus ~450 BC) Discontinuous theory of matter ALCHEMY Greeks (Aristotle ~350 BC)) Continuous theory of matter