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Development of the Atomic Theory. From Democritus to Dalton. Democritus. Greek philosopher 400 BC All matter is made up of atoms Atoms are solid and indestructible Atomos = ‘ indivisible ’ No experiments to support idea. The Atom.
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Development of the Atomic Theory From Democritus to Dalton
Democritus • Greek philosopher • 400 BC • All matter is made up of atoms • Atoms are solid and indestructible • Atomos = ‘indivisible’ • No experiments to support idea
The Atom • The smallest particle of an element that retains the properties of that element • Basic building block of matter
Learning Check #1 • What does the word indivisible mean? • What is an atom? • Who first proposed the idea of atoms? • The smallest particle of an element that retains the properties of that element • Cannot be split! • Democritus
Antoine Laviosier (1774) • Developed the Law of Conservation of Mass • Matter, like energy, is neither created nor destroyed in an ordinary chemical reaction • “One may take it for granted that in every reaction there is an equal quantity of matter before and after.”
Joseph Proust • Developed Law of Definite Proportions • Any given compound always contains the same elements in the same proportions by mass. • Example – Water is always 88.9% oxygen and 11.1% hydrogen by mass
Learning Check #2 • In a chemical reaction if I start with 100 g of material, how many grams should be there at the end? • In a compound, what do we know about the ratio of elements? • Who developed the Law of Conservation of Mass? • 100 g • Always the same! • Antoine Lavoisier
John Dalton (1803) • English school teacher • Developed the first atomic theory. • First attempt, using experimentation, to prove the existence of atoms and explain the structure of matter
Four Parts of Atomic Theory • All matter is composed of tiny indivisible particles called atoms. • All atoms of the same element are identical but are different from atoms of other elements. • A chemical compound always contains the same atoms in the same ratio. • In chemical reactions, atoms from one or more compounds or elements rearrange to form one or more new compounds. New elements are not formed.
Learning Check #3 • According to Dalton, all matter is made up of? • Are all atoms of silver the same? What part of Dalton’s theory supports your answer? • Are new elements formed in a chemical reaction? • Indivisible atoms • Yes. Part #2. • No.