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Development of Atomic Theory. Unit 2 Chapter 4, Section 1. Democritus vs. Aristotle. source. source. Matter cannot be divided forever. Matter is composed of atoms - solid, homogeneous, indivisible particles. Different kinds of atoms have different shapes.
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Development of Atomic Theory Unit 2 Chapter 4, Section 1
Democritus vs. Aristotle source source
Matter cannot be divided forever. Matter is composed of atoms - solid, homogeneous, indivisible particles. Different kinds of atoms have different shapes. Changes in matter result from changes in groupings of atoms. Atoms move through empty space. Matter can be subdivided into smaller and smaller particles forever. Matter is composed of combinations of air, earth, fire, and water. No such thing as empty space. Had the “ether.” Aristotle 350 B.C. Democritus400 B.C. What holds atoms together?
For 2000 years most people believed that the 4 elements were air, earth, water, and fire.And there was no such thing as empty space! Aristotle won that debate!
Antoine LaVoisier • Demonstrated the importance of measurements in chemistry. • Very interested in combustion. • - Corrosion of metals • - Respiration • Disproved the phlogiston theory. • First stated Law of Conservation of Mass.
LaVoisier was the father of modern chemistry, but he lost his head in 1794!
Phlogiston Theory • wood calx (ash) + phlogiston (to the air) • iron calx (rust) + phlogiston (to the air) • They weren’t too clear on the difference between heat (a form of energy) and matter.
J. Proust – 1797Law of Definite Proportions • In a pure compound, the elements combine in definite proportions to each other.
John Dalton & Atomic Theory 1803 source source
Dalton’s Atomic Theory • Matter is composed of very small particles – atoms. • All atoms of a given element are identical.* • Atoms of different elements are different. • Atoms are indivisible and cannot be created or destroyed.* • Different atoms combine in whole number ratios to form compounds. • In a reaction, atoms are rearranged.
So Dalton’s atoms are kind of like billiard balls. Atoms combine in whole-number ratios.
So how big is an atom? • Most atoms are 1-2 angstroms across. • An angstrom = 1 X 10-10 m. • 6 Billion Cu atoms in a line – less than 1 meter! • Can we “see” an atom?
