Download Atomic Structure

Match the scientist to the following
Dalton
Rutherford
Thomson
1.
2.
3.
4.
5.
6.
7.
8.
Atoms are small indivisible spheres.
Atoms have a positively charged nucleus.
Atoms have negative electrons.
“plum pudding” model.
Planetary model
Gold Foil experiment.
Created original atomic theory.
Experimented with cathode rays.
Atomic Structure
Chapter 4
Models of the Atom
Sections 4.1 and 4.3
Dalton’s Atomic Theory
• Proposed by John Dalton (English
schoolteacher) in 1803.
Dalton’s Atomic Theory
 All elements are composed of indivisible
particles called atoms.
 All atoms of the same element have the
same mass, and atoms of different
elements have different masses.
 Compounds contain atoms of more than
one element.
 In a compound, atoms of different
elements always combine in the same
way.
Evidence for Atoms
• Dalton was able to explain the law of
definite composition, law of conservation
of mass and other scientific observations.
• He later used the law to develop the law of
multiple proportions which further
supported the theory.
Visual Representation
• Dalton thought atoms were like solid
spheres.
Using Analogies
You only need to copy what is in bold print!
The network of blood vessels is like the network of
streets and highways in a large city. How are the two
networks similar? Both networks are used to transport
objects from one location to another. This comparison is
an example of an analogy. An analogy uses a similarity to
compare two objects or systems. A familiar item is often
used to compare a less familiar object.
1.Atoms in compounds are like bricks in a wall.
Explain this analogy.
2.Think of another analogy for atoms in compounds.
Thomson’s Model of the Atom
• J.J. Thomson
• 1897
Thomson’s Experiments
• Thomson was investigating the beams
inside a cathode ray tube
• He noticed that the beam inside the tube
would bend when passed between two
charged plates.
Evidence for Subatomic Particles
• Particles had to have negative charge
because they were attracted to the
positive plate.
• Had to come from inside atoms
– Particles were always the same no matter
what metal was used to produce them.
– The particles had 1/2000th the mass of the
smallest known element (hydrogen)
• Thomson’s experiments provided the first
evidence that atoms are made from even
smaller particles.
Thomson’s Model of the Atom
• Atoms are neutral so if they contain negative
charges, they must also contain positive
charges.
• In Thomson’s model the negative charges are
evenly scattered throughout positively charged
matter in the rest of the atom.
• He called it the “Plum Pudding” model
(Chocolate chip ice cream might be an
analogy you are more familiar with.)
Plum Pudding
Visual representation
Rutherford’s Atomic Model
• Ernest Rutherford
• 1911
Rutherford’s Hypothesis
• Was experimenting with positively charged
alpha particles that were emitted from
uranium.
• Thought that when they passed through a
thin sheet of gold foil they should pass
right through based on Thomson’s model
of the atom.
The Gold Foil Experiment
• Alpha particles could be detected on a screen
surrounding the gold foil as a flash of light.
• Most particles passed straight through the foil
but 1/20,000 was deflected by more than 90°.
• Since a very small number of alpha particles
were deflected and most passed straight
through, Rutherford concluded that the positive
charge in the atom is concentrated in small,
central area called the nucleus.
“It was quite the most incredible event that has
ever happened to me in my life. It was almost
as incredible as if you fired a 15-inch shell at a
piece of tissue paper and it came back and hit
you.”
-Ernest Rutherford discussing the results of his
experiment.
Rutherford’s Model
• The nucleus is a dense, positively
charged mass in the center of the atom.
• If the atom was the size of a sports
stadium the nucleus would be the size of a
marble.
• The nucleus contains almost all of an
atoms mass.
• The negatively charged electrons orbit the
nucleus like planets around the sun.
Visual Representation