Section 4.1 Studying Atoms
This section discusses the development of atomic models.
Reading Strategy (page 100)
Summarizing As you read, complete the table about atomic models. For more information on this Reading Strategy, see the Reading and Study Skills in the Skills and Reference Handbook at the end of your textbook.
Ratio of masses
Indivisible, solid spheres
Negative charges evenly scattered through
positively charged mass of matter
(plum pudding model)
Deflection of alpha particles
passing through gold foil
Positive, dense nucleus
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Ancient Greek Models of Atoms (page 100)
1. Democritus named the smallest particles of matter
because they could not be divided.
2. List the four elements that Aristotle included in his model of matter. Earth
Dalton’s Atomic Theory
3. Is the following sentence true or false? John Dalton gathered evidence for the existence of atoms by measuring the masses of true
elements that reacted to form compounds.
4. What theory did Dalton propose to explain why the elements in a compound always join in the same way? He proposed that all matter is made up of individual particles called atoms, which cannot be divided.
5. Circle the letters of the sentences that represent the main points of Dalton’s theory of atoms.
a. All elements are composed of atoms.
b. In a particular compound, atoms of different elements always combine the same way.
c. All atoms have the same mass.
d. Compounds contain atoms of more than one element.
Physical Science Reading and Study Workbook
Thomson’s Model of the Atom
6. Objects with like electric charges
, and objects with
opposite electric charges
7. What happened to the beam when Thomson placed a pair of charged metal plates on either side of the glass tube? The beam was attracted by the positively charged plate and repelled by the negatively charged plate.
8. Thomson concluded that the particles in the glowing beam had a(n) negative
charge because they were attracted to a positive plate.
9. Is the following sentence true or false? Thomson’s experiments provided the first evidence for the existence of subatomic particles. true
10. Describe Thomson’s model.
Negative charges are evenly scattered throughout an atom filled
with positively charged mass of matter.
Rutherford’s Atomic Theory
11. What is an alpha particle?
An alpha particle is a fast-moving particle that carries
a positive charge.
12. Fill in the table to show what Rutherford hypothesized would happen to the paths of alpha particles as they passed through a thin sheet of gold.
Particles that did not pass straight
from their source to a screen that lit up
through would be deflected only slightly.
13. Circle the letters of the sentences that describe what happened when Marsden directed a beam of particles at a piece of gold foil. a. Fewer alpha particles were deflected than expected.
b. More alpha particles were deflected than expected.
c. None of the alpha particles were deflected.
d. Some alpha particles bounced back toward the source.
14. Circle the letter of the sentence that states what Rutherford concluded from the gold foil experiment.
a. An atom’s negative charge is concentrated in its nucleus. b. Thomson’s model of the atom was correct.
c. An atom’s positive charge is concentrated in its...
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