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Review 4.1/4.2
1. The ancient Greek philosopher, Democritus, believed that all matter consisted of extremely small particles that
could not be divided.
2. The Greek philosopher, mentioned in the previous question, thought that there were different types of atoms
with specific sets of properties. (true, false)
3. Aristotle thought that all matter was built up from only four elements. These elements were
earth, air, fire, and water
4. Dalton suggested that compounds have a fixed composition. Explain that statement.
No matter how large or small the sample, the ratio of the masses in the compound is always the same.
5. Dalton proposed that atoms could be divided into smaller particles. (true, false)
6. The main points of Dalton’s theory of the atom are:
• All elements are composed of 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 particular compound, atoms of different elements always combine in the same way
7. Sketch the device Thomson used in his experiments.
See p. 103
8. Your text states that the glowing beam in Thomson’s device bent toward a positively charged plate. What does
this tell you about the charge on the particles making up the beam?
Bending toward a positive plate indicates that the beam was negatively charged.
9. Thomson’s experiment provided the first evidence that
atoms are made of even smaller particles.
10. Describe Thomson‘s model.
A positively-charged mass of material in which negatively charged particles (plums) were distributed
11. The term used to describe Thomson’s model of the atom is the
“plum pudding model”
12. Sketch the device used in Rutherford’s gold foil experiment.
See p. 104
13. Describe the particles shot at the gold foil in Rutherford’s experiment?
The particles were fast-moving, positively -charged and emitted by uranium (alpha particles)
14. Based on Thomson’s model, what did Rutherford expect to happen when he performed his gold foil
experiment? Rutherford expected almost all of the particles to pass straight through the gold foil.
15. What was the outcome of Rutherford’s experiment?
More particles than expected were deflected and some of the particles bounced straight back.
16. What did Rutherford conclude from the results of his experiment? Rutherford concluded that the positive
charge is not evenly distributed throughout the atom; instead, it is concentrated in a very small , central
region he called the nucleus.
17. The nucleus is the dense, positively charged mass located in the center of an atom.
18. Complete the following table. (see p109)
Particle
Symbol
Relative Charge
Relative Mass
(proton=1)
Actual Mass
(g)
Location
electron
e-
1-
1/ 1836
9.11 x 10 -28
1+
1
1.674 x 10 -24
around
nucleus
nucleus
proton
p+
neutron
n
0
1
1.675 x 10 -24
nucleus
19. Each nucleus must contain at least one proton. (true, false)
20. Each nucleus must contain at least one neutron. (true, false)
21. Scientist who designed an experiment to show the existence of the neutron. Chadwick
22. Scientists are unable to see inside an atom, so what they know about subatomic particles is based on
observations of how the atoms behave in various situations.
23, The atomic number tells us the number of protons in a nucleus and what element we are investigating.
24, The number of protons in an element must be balanced by the same number of electrons to make the atom
electrically neutral.
25. The mass number is the sum of protons and neutrons in the nucleus of an atom.
26. To calculate the number of neutrons in a nucleus what operation do you perform?
atomic mass - atomic number = number of neutrons
27. Why do isotopes of an element have different mass numbers? The number of neutrons vary in different
isotopes of the same element. That is the reason why isotopes have different mass numbers.
28. With most elements, it is difficult to notice any difference in the physical or chemical properties of the isotopes.
(true, false)
29. The name we would give to an isotope of oxygen having 8 protons and 9 neutrons would be
Oxygen-17