Chemistry Essentials
Chapter 3 Homework
Answers
Pages 86-90: 2, 6, 9, 10, 11, 12, 14, 15, 16, 17, 18, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33,
34, 35, 37, 38, 39, 40, 41, 42, 43, 45, 46, 47, 48, 50, 52, 54, 55, 56, 57, 59
2. Alchemists discovered many elements and were the first to prepare several common acids.
6. The four most abundant elements in living creatures are oxygen, carbon, hydrogen, and
nitrogen. NO, in the nonliving world, the most abundant elements are oxygen, silicon, aluminum,
and iron.
9. a) Ne, b) Ni, c) K, d) Si, e) Ba, f) Ag
10.
Symbol
Fe
Cl
S
U
Ne
K
Name
iron
chlorine
sulfur
uranium
neon
potassium
11. a) copper b) cobalt c) calcium d) carbon e) chromium f) cesium g) chlorine, h) cadmium
12. a) False, Most substances in nature occur as mixtures.
b) False, A compound always contains the same relative number of atoms of its
various
elements
c) False. Atoms are made up of protons, neutrons, and electrons. OR Molecules are made up
of tiny particles called atoms.
14. A compound is a substance that is made of two or more elements that are chemically
combined in a fixed ratio.
15. If a given compound always contains the same relative numbers of atoms of each kind, and
those atoms have the same average atomic masses, then the compound made from those
elements always contains the same relative masses of its elements
16. a) PCl3 b) B2H6 c) CaCl2 d) CBr4 e) Fe2O3 f) H3PO4
17. a) False. Thomson obtained beams of identical particles whose nature did not depend on
which metal was used to generate them.
b) True
c) False. The atom was envisioned as a sphere of positive charge in which negatively charged
electrons were randomly distributed.
18. a) False. Rutherford’s bombardment experiments with metal foil suggested that alpha
particles were deflected by approaching a large, positively charged atomic nucleus.
b) False. The proton and electron have opposite electrical charges, but the mass of the electron is
much smaller than the mass of the proton.
c) True
22. electrons
23. False. Atoms that have the same number of protons but different numbers of neutrons are
called isotopes.
24. False. It represents the number of protons and neutrons in the nucleus.
25. The statement that all atoms of a given element are identical had to be modified.
26. No, all atoms of the same element are not identical. They can differ in the number of
neutrons in their nuclei, so they would have different masses.
27. a) 32 b) 30 c0 24, d) 74 e) 38 f) 27 g) 4 h) 3
28. a) 178 O b) 3717Cl c) 6027Co d) 5726Fe e) 13153I f) 73Li
29. a) 24494Pu
# protons = atomic number = 94, # electrons = # protons = 94, # neutrons = mass # - atomic
number = 244-94 =150
b) 24195Am
# protons = atomic number = 95, # electrons = # protons = 95, # neutrons = mass # - atomic
number = 241-95 =152
c) 22789Ac
# protons = atomic number = 89, # electrons = # protons = 94, # neutrons = mass # - atomic
number = 244-94 =150
d) 13355Cs
# protons = atomic number = 55, # electrons = # protons = 55, # neutrons = mass # - atomic
number = 133-55 = 78
e)19377Ir
# protons = atomic number = 77, # electrons = # protons = 77, # neutrons = mass # - atomic
number = 193-77 = 116
f) 5625Mn
# protons = atomic number = 25, # electrons = # protons = 25, # neutrons = mass # - atomic
number = 56-25 = 31
30.
Name
Symbol
Atomic
Mass Number
Neutrons
Number
23
12
sodium
11
23
11Na
15
nitrogen
7
15
8
7N
136 Ba
barium
56
136
80
56
9
3
9
lithium
6
3Li
11
B
6
boron
5
11
5
sodium: # neutrons = mass number – atomic number = 23-11 = 12
15
7N: atomic number = 7 = nitrogen # neutrons = mass number – atomic number = 15-7 = 8
136
56Ba:atomic number = 56 = barium # neutrons = mass number – atomic number = 136-56 = 80
Lithium: atomic number = 3 mass number = atomic number + number of neutrons = 3+6 = 9
Boron: # neutrons = mass number – atomic number = 11-5 = 6
31. The elements in the Periodic Table are listed in order of increasing atomic number ( number
of protons in the nucleus), although it can also be said it is arranged by the number of electrons
in the atom, as the number and arrangement of electrons determines the properties of an atom.
32. Elements with similar properties are aligned vertically on the Periodic Table. Such families
are called Groups.
33. Metallic elements are excellent conductors of heat and electricity. They are also malleable,
ductile, and generally shiny when a fresh surface is exposed.
34. Metallic elements are found at the left and bottom or the PT. There are more metallic
elements than nonmetallic elements.
35. The metallic element that is not solid at room temperature is mercury. It is a liquid at room
temperature.
37. Mercury is a metallic element that occurs as a liquid under normal conditions. Bromine is a
nonmetallic element that occurs as a liquid under normal conditions.
38. A metalloid is an element that has some properties that are common to both metals and
nonmetals. The metalloids are found in the “stairstep” region of the PT.
39. a) Iodine: Group 17 ( or 7) halogens b) Ca: Group 2 alkaline earth metals c) Na: Group 1
alkali metals d) lithium: group 1 alkali metals e) Kr: Group 18(or 8) Noble gases f) sodium:
Group 1 alkali metals g) Ne Group 18 ( or 8) noble gases
40. a) rubidium: Rb, atomic number 37, Group 1, metal b) germanium: Ge atomic number 32
Group 14 ( or 4), metalloid c) magnesium: Mg, atomic number 12, Group 2, metal d) titanium:
Ti, atomic number 22, Group 4, (transition)metal e) iodine: I, atomic number 53 Group 17(or 7)
halogen
41. Most elements are reactive, so they are found in nature in compounds.
42. The elements in group 18 are called the inert or Noble gases because they do not readily
react with other elements to form compounds.
43. The gaseous diatomic elements are hydrogen, nitrogen, oxygen, fluorine, and chlorine. The
gaseous monatomic elements are helium, neon, argon, krypton, xenon, and radon.
45. charge = protons – electrons; electrons = protons - charge
1) Al3+ = 13 -3 =10(b) 2) Fe3+ = 26 – 3 = 23(d) 3) Mg2+ = 12-2 = 10(b) 4) Sn2+ = 50-2 = 48(h)
5) Co2+ = 27-2 = 25 6) Co3+ = 27-3 = 24(e) 7) Li+ = 3-1 = 2 (a) 8) Cr3+ = 24 – 3 = 21 (c) 9) Rb+
= 37-1 = 36(g) 10) Pt2+ = 78-2 = 76(i)
46.
Cation
# protons in ion
# electrons in ion
Formula with O219
18
K2O
K+
2+
27
25
CoO
Co
13
10
Al2O3
Al3+
K+: # protons = atomic number = 19, #electrons = # protons – charge = 19-1 = 18
Co2+: # protons = atomic number = 27, #electrons = # protons – charge = 27- 2 = 25
Al3+: # protons = atomic number = 13, #electrons = # protons – charge = 13-3 = 10
Anion
ClS2P3-
# protons in ion
17
16
15
# electrons in ion
18
18
18
Formula with Ca2+
CaCl2
CaS
Ca3P2
Cl-: # protons = atomic number = 17, #electrons = # protons – charge = 17-(-1) = 18
S2-: # protons = atomic number = 16, #electrons = # protons – charge = 16- (-2) = 18
P3-: # protons = atomic number = 15, #electrons = # protons – charge = 15-(-3) = 18
47. a) Ca: # protons = atomic number = 20, # electrons = # protons = 20 Ca2+: # protons =
atomic number = 20, # electrons =# protons – charge = 20-2 = 18
b) P: # protons = atomic number = 15, # electrons = # protons = 15 P3-: # protons =
atomic number = 15, # electrons =# protons – charge = 15- (-3) = 18
c) Br: # protons = atomic number = 35, # electrons = # protons = 35 Br-: # protons =
atomic number = 35, # electrons =# protons – charge = 35-(-1) = 36
d) Fe: # protons = atomic number = 26, # electrons = # protons = 26 Fe3+: # protons =
atomic number = 26, # electrons =# protons – charge = 26-3 = 23
e) Al: # protons = atomic number = 13, # electrons = # protons = 13 Al3+: # protons =
atomic number = 13, # electrons =# protons – charge = 13- 3 = 10
f) N: # protons = atomic number = 7, # electrons = # protons = 7 N3-: # protons = atomic
number = 7, # electrons =# protons – charge = 7- (-3) = 10
48. a) 53: I forms I- b) 38: Sr forms Sr2+ c) 55: Cs forms Cs+ d) 88: Ra forms Ra2+ e) 9: F
forms F- f) 13: Al forms Al3+
50. When the compound is melted, the electrons can move freely between atoms, so electricity
can be conducted. In the solid state, the ions are held tightly in place, so there is no way for the
electrons to move, and no electricity is conducted.
52. a) FeP b) Fe2S3 c) FeCl3 d) MgCl2 e) MgO f) Mg3N2 g) Na3P h) Na2S
54. Most of the mass of the atom comes from the protons and the neutrons. The electrons
determine the chemical properties of an atom.
55. Yes, two elements can form more than one compound. It is consistent with Dalton’s theory
because each compound will have a different relative numbers and types of atoms. An example
is the different compounds nitrogen and oxygen can form – NO, NO2, N2O, etc.
56. a) CO2 b) AlCl3 c) HClO4 d) SCl6
57. a) +1 b) -2 c) +2, d) -1
59. a) atomic number = number of protons = 11 = sodium mass number = atomic number +
number of neutrons = 11+12= 23 2311Na
b) ) atomic number = number of protons = 11 = sodium mass number = atomic number +
number of neutrons = 11+13= 24 2411Na
c) ) atomic number = number of protons = 12 = magnesium mass number = atomic
number + number of neutrons = 12 + 12 = 24 2412Mg