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Discovery of the Atom

Discovery of the Atom. Democritus. Democritus was an ancient Greek who had a philosophical idea of an atom. His approach was not based on the scientific method. Dalton. Dalton transformed the philosophical concept of an atom into a scientific theory . A.)

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Discovery of the Atom

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  1. Discovery of the Atom

  2. Democritus • Democritus was an ancient Greek who had a philosophical idea of an atom. • His approach was not based on the scientific method.

  3. Dalton • Dalton transformed the philosophical concept of an atom into a scientific theory. • A.) • All elements are composed of indivisible atoms. • What does indivisible mean? • Cannot be divided. • B.) • Atoms of the same element are identical. • Atoms of different elements are different. • C.) • Atoms combine in fixed ratios to form compounds. • D.) • Chemical reactions occur when atoms are rearranged.

  4. What does subatomic mean? • Smaller than atomic

  5. What are the three kinds of subatomic particles? • Protons, Neutrons and Electrons

  6. Who discovered the electron? • J.J. Thomson

  7. What did the cathode-ray tube experiment allow to be concluded? • Electrons are in ALL atoms.

  8. Millikan • Millikan found the quantity of chargecarried by an electron. • This allowed the calculation of the mass of the electron. It’s mass is 1/1840 the mass of a hydrogen atom.

  9. Atoms are electrically neutral. • Positively charged subatomic particles are called protons. • Subatomic particles with no charge are called neutrons.

  10. Rutherford • Rutherford’s gold-foil experiment gave evidence of the atomic nucleus. • Alpha particles were aimed at a sheet of gold foil.

  11. Rutherford’s Gold Foil Experiment • Most of the particles passed through. • A few of the particles bounced back. • It was concluded that an atom is mostly empty space. • The mass and positive charge are concentrated in the nucleus.

  12. Atom Make-Up • The protons and neutrons are located in the nucleus. • The electrons are distributed around the nucleus and occupy • almost all of the volumeof the atom.

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