Title: Structure of the Atom - Models
1Structure of the Atom - Models
- Chapter 19 Section 1 Part 2
- Pages 580-583
2Models 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.
3The 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
4The Changing Atomic Model Figure 5, page 582
- 2. In the 1700s emphasis was placed on careful
and repeated measurements.
5The 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.
6The 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
7The 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
8The 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
9The Changing Atomic Model Figure 5, page 582
- 7. James Chadwick (1913) Rutherfords student
- - Nucleus contains neutral neutrons and positive
protons
10The 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.
11Electron Cloud Model / Modern Atomic Model
- Impossible to accurately locate an
- electron at any given time.