Chapter 4 Review
1. Word Origins The word electron was formed by combining the root electr-, meaning amber, with the suffix –on . List at least three other words that include the root electr.
U S I N G K EY T E RMS
2. How many protons and neutrons does a silicon,
Si, atom have, and where are these two types of subatomic particles located? How many electrons does a silicon atom have?
3. Explain why different atoms of the same element always have the same atomic number but can have different mass numbers.
What are these different atoms called?
4.
What does an element’s molar mass tell you about the element?
5. What is an orbital?
UNDERSTAND I N G K EY I DEAS
6. Which of Dalton’s statements about the atom was proven false by J. J. Thomson? a. Atoms cannot be subdivided. b. Atoms are tiny. c. Atoms of different elements are not identical. d. Atoms join to form molecules.
7. What did Rutherford learn about the atom from his gold-foil experiment? a. Atoms have electrons. b. Atoms have a nucleus. c. Atoms have negative charge embedded in a sphere of positive charge. d.
The nucleus is most of the atom’s volume.
8. If an atom has a mass of 11 u and contains five electrons, its atomic number must be a. 55. c. 6. b. 16. d. 5.
9. Which statement is not true of Bohr’s model of the atom? a. Electrons cannot be between energy levels. b. Electrons orbit the nucleus. c. An electron’s path is not known exactly. d. Electrons exist in energy levels.
10. According to the modern model of the atom, a. moving electrons form an electron cloud. b. electrons and protons circle neutrons. c. neutrons have a positive charge. d. the number of protons for a given element varies.
11. Carbon has six protons. How many valence electrons does carbon have? a. 2 c. 6 b. 4 d. 12
12. The second energy level has 1 s orbital and 3 p orbitals. How many electrons can this energy level hold? a. 2 c. 18 b. 8 d. 32
13. An electron moves from the ground state to an excited state when it absorbs a. a proton. c. a photon. b. a neutron. d. an isotope.
E X P L A INI N G K EY I DEAS

14. Study the graphic below of
Rutherford’s goldfoil experiment. Which of the deflections, A or B, was a surprise to Rutherford? Why? show three atoms. Use the diagrams to answer questions 18–20.
15. Identify the particles that make up an atom.
How do these particles relate to the identity of an atom?
16. Determine the atomic number and mass number of an isotope that has 56 electrons and
82 neutrons.
17. Why do most atoms have no charge even though they are made up of positively charged protons and negatively charged electrons?
INTERPRETING GRAPHICS The diagrams below
18. Which diagrams represent the same element?
19. What is the atomic number for atom A?
20. What is the mass number for atom B?
CR I T I C A L TH I N KI NG
21. Applying Ideas Particle accelerators are de vices that speed up charged particles in order to smash them together. Scientists use the de vices to make atoms. How can scientists determine whether the atoms formed are a new element or a new isotope of a known element?
22. Making Inferences Why is measuring the size of an atom difficult?
23. Drawing Conclusions Are hydrogen-3 and helium-3 isotopes of the same element?
Explain.
24. Making Inferences Some forces push atoms apart, and other forces pull atoms together.
Describe how the subatomic particles in each atom interact to produce these forces.

25. Analyzing Methods If scientists had tried to repeat Thomson’s experiment and found that they could not, would Thomson’s conclusion still have been valid? Explain your answer.
26. Interpreting Graphs Study the graph of mass
(g) versus amount (mol) for iron. a. Is the relationship between the two variables direct or inverse? b. How many particles are there in 111.6 g of iron?
27. Converting Grams to Moles For an experiment you have been asked to do, you need 1.5 g of iron. How many moles of iron do you need?
28. Converting Moles to Grams Robyn recycled
15.1 mol of aluminum last month. What was the mass in grams of the aluminum she recycled?
Answers
Reading Toolbox
1. Answers may vary. Possible answers include: electric, electrical, electricity, electrocution, electromagnetic, electronic.
Using Key Terms
2. In the nucleus, a silicon atom has 14 protons, and it usually has
14 neutrons. A silicon atom has
14 electrons, four of which are

valence electrons.
3. Atomic number tells the number of protons in the atom. All atoms of the same element have the same number of protons, so they have the same atomic number.
The mass number is the total number of protons and neutrons in an atom. The number of neutrons can vary, so the mass number can vary among atoms of the same element. These different atoms are called isotopes.
4. The molar mass is the mass of one mole, or 6.022 × 10
23 particles, of the element.
5. An orbital is a region in the atom where there is a high probability of finding electrons.
Understanding Key Ideas
6. a
7. b
8. d
9. c
10. a
11. b
12. b
13. c
Explaining Key Ideas
14. Deflection A was a surprise because Rutherford didn’t expect the positive charge in the atom to be concentrated enough to deflect a positive charge back at such a large angle.
15. The particles that make up an atom are protons, neutrons, and electrons. The number of protons determines the atom’s atomic number. In a neutral atom, this number also equals the number of electrons.
16. Z = 56, A = 138
17. Most atoms have no overall charge because they have equal numbers of protons and electrons, so the positive and negative charges exactly cancel one another.
18. a and c
19. Z = 3 for a
20. A = 7 for b
Critical Thinking
21. Scientists must determine the atomic number, or the number of protons, in the newly formed nucleus. The nucleus is that of a new element only if the number of protons is different from all known elements.
22. It is difficult to measure the size of an atom because atoms are very small. In addition, some atoms do not exist for very long due to their radioactivity.
23. No, they are not isotopes of the same element. They have the same mass number, but different numbers of protons. It is the number of protons that defines the element.
24. Because like charges repel each other and unlike charges attract, protons repel each other and attract electrons. Electrons repel each other and attract protons.
Since protons in the nucleus repel each other, there must be a stronger force that holds them together in the nucleus.
25. No, the results of an experiment must be repeatable to be considered valid.
Graphing Skills
26. a. direct b. The graph shows that 111.6 g corresponds to 2 mol: 2 mol ×
(6.022 × 10
23 particles/mol) =
1.204 × 10
24 particles
Math Skills
27. 1.5 g Fe × 1 mol Fe/55.85 g Fe = 0.027 mol Fe
28. 15.1 mol Al × 26.98 g Al/1 mol Al = 407 g Al