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Structure of the Atom - Models

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Title: Structure of the Atom - Models


1
Structure of the Atom - Models
  • Chapter 19 Section 1 Part 2
  • Pages 580-583

2
Models Tools for Scientists
  • Models are used to represent things that are
    difficult to visualize / see, or picture in the
    mind.
  • Models must accurately represent all information
    known about what is being modeled.

3
The Changing Atomic Model Figure 5, page 582
  • - Models of the atom have changed through time.
  • 1. Democritus (400 B.C.) ? Greek philosopher
  • ? Three main ideas about matter
  • a. Universe made of invisible units, called them
    atomos
  • ? Atomos means uncuttable
  • b. Movements of these atoms caused the
  • observed changes in matter.
  • c. Theory explains some of his observations
  • - Lacked evidence

4
The Changing Atomic Model Figure 5, page 582
  • 2. In the 1700s emphasis was placed on careful
    and repeated measurements.

5
The Changing Atomic Model Figure 5, page 582
  • 3. John Dalton (1808)
  • English school teacher
  • - Widely accepted atomic theory due to supporting
    evidence.
  • - 3 main points
  • a. Every element is made of
  • tiny unique particles
  • (atoms) that cannot be
  • divided.
  • b. Atoms of the same
  • element are exactly alike.
  • c. Atoms of different
  • elements can join to form
  • molecules.

6
The Changing Atomic Model Figure 5, page 582
  • 4. Joseph John Thomson (1904) English physicist
  • - Inferred by experimentation that atoms
  • contain negatively charged particles
  • ? electrons
  • - Thought electrons were
  • evenly embedded in
  • positively charged sphere.
  • ? Like chocolate chip cookie
    dough

7
The Changing Atomic Model Figure 5, page 582
  • 5. Ernest Rutherford (1911) British physicist
  • - Proposed most of an atoms mass (all the
  • positive charge)
  • is in the nucleus
  • Nucleus surrounded
  • by electrons
  • - Gold Foil experiment

8
The Changing Atomic Model Figure 5, page 582
  • 6. Neils Bohr (1913) Danish physicist
  • - Proposed that
  • electrons orbit
  • nucleus in fixed
  • paths
  • - Like planets
  • orbiting the sun

9
The Changing Atomic Model Figure 5, page 582
  • 7. James Chadwick (1913) Rutherfords student
  • - Nucleus contains neutral neutrons and positive
    protons

10
The Changing Atomic Model Figure 5, page 582
  • 8. Electron Cloud model (1926) the current
    model
  • - Electrons do not follow fixed orbits
  • - Tend to occur more frequently in certain
  • areas around nucleus
  • ? Looks like a fan blade spinning
  • - This model basically describes a cloud-like
    region
  • where the electron is likely to be found.

11
Electron Cloud Model / Modern Atomic Model
  • Impossible to accurately locate an
  • electron at any given time.
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