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Unit 2: The Atom

Textbook Chapter 5 & 13 Review Book Topic 1. Unit 2: The Atom. Atomic Fundamentals. All matter is composed of tiny fundamental particles called atoms Atom – smallest particle of an element that retains the properties of that element. Examples of atomic size:

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Unit 2: The Atom

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  1. Textbook Chapter 5 & 13 Review Book Topic 1 Unit 2: The Atom

  2. Atomic Fundamentals • All matter is composed of tiny fundamental particles called atoms • Atom – smallest particle of an element that retains the properties of that element

  3. Examples of atomic size: • A pure copper coin the size of a penny contains 2.4 x 1022 atoms • Compared to the Earth’s population (6 x 109 people), there are about 4 x 1012 as many atoms in the coin as there are people on Earth • If you could line up 100,000,000 copper atoms side by side, they would produce a line on 1 cm long

  4. Early Models of the Atom • Democritus of Abdera • 4th Century B.C. – Greece • First to suggest the existence of atoms as invisible and indestructible particles • Components: Fire, Earth, Wind and Water • The real nature of atoms was not established for more than 2000 years later

  5. Robert Boyle (1600s) • Identified gold and silver as being elemental • Not made of Earth, fire, wind or water • Considered the “Father of Modern Chemistry”

  6. John Dalton (1803) • Studied the ratios in compounds • Set the groundwork for the current concept of the atom • Dalton’s Atomic Theory • Atoms cannot be broken down • Atoms of the same element are identical • Each element’s atoms are different • Atoms of different elements can chemically or physically combine to form compounds

  7. Structure of the Atom • Most of Dalton’s atomic theory is accepted today but atoms can be broken down into even smaller particles: • Protons • Neutrons • Electrons

  8. Electrons – negatively charged particles • Discovered by J.J. Thomson in 1897 • Experimented with a cathode tube • A cathode ray is composed of negatively charged particles • Negative electrical charges repels the rays, while positive charges are attracted • Refer to pages 109-110 in your textbook

  9. Called his atomic model the “plum pudding model”

  10. Robert A. Millikan (1868-1953) • An electron carries exactly one unit of negative charge • Mass of an electron is 1/1840 the mass of a hydrogen atom

  11. Protons and Neutrons • Atoms have no net electric charge • Entire atom is neutral so: (+) charges = (-) charges • So # protons = # electrons in a neutral atom!

  12. Protons – positively charged subatomic particles, each with a mass about 1840 times that of an electron • Neutron – subatomic particles with no charge but with a mass nearly equal to that of a proton • So if an atom is overall neutral…. # protons (+) = # electrons (-)

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