Chapter 2:
1. Use the atomic theory, explain the difference in the following two statements:
(a) Nitrogen dioxide is a compound of nitrogen and oxygen. (b) Air is a mixture
composed mostly of nitrogen and oxygen.
2. How does the atomic theory account for the fact that when 1.000 g of water is
decomposed into its elements, 0.111 g of hydrogen and 0.889 g of oxygen are
obtained regardless of the source of the water?
3. A chemist prepared a series of compounds containing only sulfur and fluorine
and determined the amount of each element in each compound.
Compound
Mass of sulfur (g)
Mass of fluorine (g)
A
23.2
55.0
B
16.6
9.8
C
19.3
68.6
(a) Calculate the mass of fluorine per gram of sulfur in each compound. (b) How do
the numbers in part (a) support the atomic theory?
Ans: A is 2.37:1; B is 0.590:1; C is 3.55:1; all three compounds are 4:1:6 for S
4. A chemistry student finds that 15.20 g of nitrogen will react with 17.37 g, 34.74 g, or
43.43 of oxygen to form three different compounds. (a) Calculate the mass of oxygen
per gram of nitrogen in each compound, (b) How do the numbers in part (a) support
the atomic theory? Ans: (a) 1.14/1.14; 2.29/1.14; 2.86/1.14; (b) 2:4:5
5. Natural gas (methane) burns in the presence of oxygen to produce water, carbon
dioxide, and heat. We know that 4.0 g of natural gas requires 16.0 g of oxygen for
complete combustion and that 9.0 g of water is produced in this reaction. Can the mass
of carbon dioxide produced be determined from this information? Explain.
Ans: prove by Law of Conservation of Mass
6. What was the evidence used to conclude that cathode rays consist of negatively
charged particles? Ans: magnetic fields deflect rays (like charges repel)
7. A negatively charged particle is directed between two electrically charged plates such
as those shown in Figure 2.9. (a) Why does the path of the charged particle bend? (b)
As the charge on the plates is increased, would you expect the mass of the particle is
increased, decrease or stay the same? (c) As the mass of the particle is increased,
would you expect the bending to increase, decrease, or stay the same?
Ans: like charges repel; increase; decrease
8. Static electricity, such as that given to a piece of amber by rubbing it with wool, is due
to a buildup of electrons. A sample of amber is measured to have a static piece of 3.24
X 10-6 C. How many excess electrons are on the piece of amber?
Ans: 2.02 x 1013 electrons
9. Millikan determined the charge on the electron by studying the static charges on oil
drops falling in an electric field. A student carried out this experiment using several oil
drops. She obtained the following data:
Droplet
Calculated charge (C)
A
1.60 X 10-19
B
3.15 X 10-19
C
4.81 X 10-19
D
6.31 X 10-19
What value (and to how many significant figures) should she report for the electronic
charge? Ans: 1.59 x 10-19C
10. The diameter of the cesium (Cs) atom is about 4.7 A. (a) Express this distance in
nanometers (nm); in picometers (pm). (b) How many cesium atoms would have to be
lined up to span 1.0 cm? Ans: 4.7 x 10-1 nm; 4.7 x 102 pm; 2.1 x 107 atoms Cs
11. If 1.0 X 108 sodium (Na) atoms could be arranged side by side, they would form a
straight line measuring 3.1 cm. What is the diameter of an Na atom?
Ans: 3.1 x 10-8 cm/Na atom
12. How many protons, neutrons, and electrons are in the following atoms: (a) 20Ne; (b)
39
K; (c) 48Ti; (d) 80Br; (e) 109Ag; (f) 137Ba? Ans: (a) 10 p+, 10 e-, 10 n0; (b) 19, 19, 20;
( c ) 22, 22, 26; (d) 35, 35, 45; (e) 47, 47, 62; (f) 56, 56, 81
13. Each of the following nuclides is used in medicine. Indicate the number of protons
and neutrons in each nuclide: (a) cobalt-60; (b) iodine-131; (c) technetium-99; (d)
phosphorus-32; (e) chromium-51; (f) iron-59. Ans: (a) 27 p+, 33 n0; (b) 53, 78; ( c )
43, 56; (d) 15, 17; (e) 24, 27; (f) 26, 33
14. Fill in the gaps in the following table:
19
74
Symbol
F
As
Protons
56
Neutrons
81
71
Electrons
51
78
Mass no.
196
Ans: (given vertically) 19F, 9, 10, 9, 19; 74As, 33, 41, 33, 74; 137Ba, 56, 81, 56, 137;
122
Sb, 51, 71, 51, 122; 196Pt, 78, 118, 78, 196
15. Fill in the gaps in the following table:
31
Symbol
P
Protons
26
80
Neutrons
30
Electrons
53
Atomic no.
50
Mass no.
119
127
201
Ans: (given vertically) 31P, 15, 16, 15, 15, 31; 56Fe, 26, 30, 26, 26, 56;
119
Sn, 50, 69, 50, 50, 119; 127I, 53, 74, 53, 53, 127; 201Hg, 80, 121, 80, 80, 201
16. Locate each of the following elements in the periodic table, indicate whether it is a
metal, metalloid, or nonmetal, and give the name of the element: (a) S; (b) Se; (c) Hg;
(d) Ca; (e) Ne; (f) Be; (g) Zn. Ans: nm, nm, m, m, nm, m, m
17. Classify each group of 6A elements (the chalcogens) as a metal, metalloid, or
nonmetal. Ans: nm, nm, nm, metalloid, m
18. From the following list, find the groups of compounds that have the same empirical
formula: C2H2, N2O4, C2H4, C6H6, NO2, C3H6, C4H8.
Ans: C2H2 and C6H6; C2H4, C3H6 and C4H8; N2O4 and NO2
19. Which of the following ions would you not expect to form: (a) F+; (b) S2-; (c) Be-; (d)
P3-; (e) Br-; (f) K2+? Ans: F+, Be-, K+2
20. Name the following ionic compounds: (a) AlzO3; (b) Cu(ClO4)2; (c) NiCO3; (d)
SnBr2; (e) Fe(OH)2; (f) KMnO4; (g) Pb(C2H3O2)2; (h) Zn(H2PO4)2; (i) Li2SO3; (j)
(NH4)2Cr2O7. Ans: aluminum oxide, copper (II) perchlorate, nickel (II) carbonate,
tin (II) bromide, iron (II) hydroxide, potassium permanganate, lead (II) acetate, zinc
dihydrogen phosphate, lithium sulfite, ammonium dichromate
21. Give the name or chemical formula, as appropriate, for each of the following acids:
(a) HBr; (b) HbrO4; (c) HNO2; (d) hypochlorous acid; (e) iodic acid; (f) sulfuric acid.
Ans: hydrobromic acid, perbromic acid, nitrous acid, HclO, HIO3, H2SO4
22. Assume that you encounter the following phrases in your reading. What is the
chemical formula for each substance mentioned? (a) Potassium chlorate is used as a
laboratory source of oxygen. (b) Sodium hypochlorite is used as a household bleach.
(c) Ammonia is important in the synthesis of fertilizers such as ammonium nitrate. (d)
Hydrofluoric acid is used to etch glass. (e) The smell of rotten eggs is due to hydrogen
sulfide. (f) When hydrochloric acid is being added to sodium bicarbonate (baking
soda), carbon dioxide gas forms. Ans: KClO3 (g), O2 (g), NaClO (aq), NH3 (g),
NH4NO3(s), HF(aq), H2S (g), HCl (aq), NaHCO3 (s), CO2 (g)