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The Atomic Theory – p. 82-87 Democritus

The Atomic Theory – p. 82-87 Democritus. Democritus, 440 B.C. Thought matter was made of tiny particles Believed these particles could not be cut into any smaller pieces. Called this smallest particle, atom, which means not able to be divided. Dalton. British scientist

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The Atomic Theory – p. 82-87 Democritus

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  1. The Atomic Theory – p. 82-87Democritus • Democritus, 440 B.C. • Thought matter was made of tiny particles • Believed these particles could not be cut into any smaller pieces. • Called this smallest particle, atom, which means not able to be divided

  2. Dalton • British scientist • By the 1700’s scientists knew that elements combine to form different types of matter • Atoms looked like small, solid marbles • After extensive work, Dalton published his atomic theory in 1803 • All substances are made from atoms. Atoms 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

  3. J.J. Thomson • 1897 – Made a correction to Dalton’s theory • Discovered that atoms contain negatively charged particles which he called electrons • Developed the plum pudding model to describe what he believed an atom to look like • This model had the electrons located throughout the atom

  4. Rutherford • 1911- Rutherford revised atomic theory • Based on his experiments he proposed that atoms have a dense small center which he called a nucleus • This center contained positively charged particles which were called protons • Electrons surrounded the nucleus with large amounts of space between the nucleus and the electrons

  5. Bohr • 1913 – Proposed that electrons move around the nucleus in certain pathways or energy levels

  6. Modern Atomic Theory • Electron Cloud Model • Center of an atom very small and very dense. • Have positively charged particles called protons • Has particles called neutrons that have no charge • Electrons have a negative charge and move around the nucleus in orbits. These orbits do not have set paths so they look like a cloud around the nucleus

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