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Unit 4: Introduction to Atoms

Unit 4: Introduction to Atoms. Development of the Atomic Theory. What is an Atom?. An atom is the smallest particle into which an element can be divided and still be the same substance. REVIEW: Atoms make up elements; elements combine to form compounds

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Unit 4: Introduction to Atoms

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  1. Unit 4: Introduction to Atoms Development of the Atomic Theory

  2. What is an Atom? An atom is the smallest particle into which an element can be divided and still be the same substance. REVIEW: Atoms make up elements;elements combine to form compounds Because all matter is made of elements or compounds, atoms are often called the building blocks of matter.

  3. DemocritusBorn: 460b.c.Died: 370b.c. Suggested that you could cut an object in half only so many times before you would reach an “uncut-table” particle. He called this particle and atom. He suggested that all particles are small, hard and made of a single material.

  4. AristotleBorn: 384b.c.Died:322b.c. 350 B.C - Aristotle modified an earlier theory that matter was made of four “elements”: earth, fire, water, air. Aristotle was wrong. However, his theory persisted for 2000 years.

  5. John Dalton(1766-1844) All substances are made of atoms. Atoms are small particles that cannot be created, divided, or destroyed. Atoms of the same element are exactly alike, and atoms of different elements are different. Atoms join with other atoms to make new substances.

  6. J.J. Thomson(1856-1940) • Discovered that there are small particles inside the atom. • Call these positively charged particles corpuscles. • Today we call them electrons.

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