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Chapter 3.1

Chapter 3.1 . Atomic Structure. What are atoms?. In the 4 th century B.C., the Greek philosopher Democritus suggested that the universe was made of invisible units called atoms pg 70. What Are Atoms?. In 1808, English schoolteacher John Dalton proposed an atomic theory

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Chapter 3.1

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  1. Chapter 3.1 Atomic Structure

  2. What are atoms? • In the 4th century B.C., the Greek philosopher Democritus suggested that the universe was made of invisible units called atoms pg 70

  3. What Are Atoms? • In 1808, English schoolteacher John Dalton proposed an atomic theory • Every element is made up of tiny, unique particles called atoms that cannot be subdivided • Atoms of the same element are exactly alike • Atoms of different elements can join to form molecules pg 71

  4. What’s in an Atom? • At the center of each atom is a small, dense nucleus with a positive charge • Made up of protons and neutrons • Almost identical in size and mass, but protons have a positive charge while neutrons have no charge at all • Circling outside the nucleus is a cloud of very tiny negatively charged electrons with very little mass pg 72

  5. What’s in an Atom? • Atoms are not charged because they have an equal number of protons and electrons whose charges exactly cancel pg 72

  6. Models of the Atom • In 1913, Danish scientist Niels Bohr suggested that electrons move in set paths around the nucleus much like the planets orbit the sun in the solar system • Each electron has an energy level that determines its path around the nucleus • Must gain or lose energy to move to a different level pg 73

  7. Models of the Atom • By 1925, Bohr’s model of the atom no longer explained all observations • New model proposed that no longer assumed electrons orbited the nucleus along definite paths • Believed electrons behave more like waves on a vibrating string than like particles pg 73

  8. Models of the Atom • The regions in which electrons are found are called orbitals • 4 different kinds of orbitals • s orbital shaped like a sphere surrounding nucleus holding a maximum of two electrons • p orbital are dumbbell-shaped and can be oriented in three different directions with two electrons each • Five possible d and seven possible f orbitals, each with a maximum of 2 electrons pg 75

  9. Models of the Atom • An electron in the outermost energy level of an atom is called a valence electron pg 76

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