Answers to Chapter 3 Chapter Review Questions
1.
a. Atoms are neither created nor destroyed, because in chemical reactions, atoms are only rearranged.
b. Atoms of each element have their own unique and identical masses. Therefore all compounds composing them will be
composed of the same composition by mass.
c. only whole atoms combine to form compounds, therefore, different compounds with the same elements must have
mass compositions that are whole number ratios of each other as a result of the combining of different whole numbers of
atoms.
2.
A + B = 2 + 3 = 5 mass units.
3.
a. An atom is the smallest particle of an element that has the properties of that element.
b. The nucleus and surrounding electron cloud.
4.
1) negative charge
2) has mass 1 / 2,000th the mass of lightest element atoms (hydrogen)
3) is found in atoms of all elements
4) its charge / mass ratio is constant
5.
Rutherford’s model of the atom had the positive charges and mass concentrated at the nucleus, with the nucleus being very
tiny, the atom’s volume being mostly empty space, and the electrons far outside the nucleus. His gold foil experiment
helped him develop his model because he fired positively charged particles at gold atoms, and his results showed some
particles bounced off the dense nucleus.
6.
Atomic number
7.
a. 1) atoms of same element, but different masses 2) atoms with the same number of protons, but different masses
3) atoms with the same atomic number, but different masses 4) atoms of the same element, but different mass
numbers 5) atoms with the same number of protons, but different mass numbers 6) atoms with the same atomic
number, but different mass numbers 7) atoms of the same element, but different numbers of neutrons 8) atoms with the
same number of protons, but different numbers of neutrons 9) atoms with the same atomic number, but different
numbers of neutrons.
b. They belong to the same element, have the same number of protons, have the same atomic number, have the same
chemical properties.
c. The have different numbers of neutrons, different mass numbers, and different masses
8.
9.
Isotope
Silicon—28
Silicon—29
Silicon—30
P+
14
14
14
e−
14
14
14
2A + 3B = 2(2) + 3(3) = 4 + 9 = 13 mass units.
n0
14
15
16
It’s the number of protons in the atoms of the element; it is used to identify the element
b. The number of protons plus neutrons
c. atomic number = 1, and the mass number = 2
10. A nuclide is any particular atom/isotope of an element
11. a. Helium—4
12. a. Carbon—12
13. a. 4 amu
b. Oxygen—16
c. Potassium—39
b. 12 amu exactly
b. 54 amu
14. a. Mole is a number, 6.022 × 1023, by definition it is the number of particles equal to the number of atoms in exactly 12
grams of carbon—12.
b. mol c. 6.022 × 1023 d. Avogadro’s number
15. a. The mass of one mole of atoms of that element
b. 12.01, 20.18, 55.85, and 238.03
16. a. Use the conversion factor that divides the mass by the molar mass. B. Use the conversion factor that divides the mass
by the molar mass, then use the conversion factor that multiplies by Avogadro’s number
17. a. 6.94 g Li
b. 27.0 g Al
18. a. 1.000 mol Ne
c. 40.1 g Ca
b. 0.5000 mol Mg
d. 55.9 g Fe
e. 12.01 g C
f. 107.9 g Ag
d. 2.81 × 10−13 mol O
c. 1,570 mol Pb
19. 39.95 amu
20. 10.00 amu
21. a. 9.03 × 1023 atoms Na
22. a. 9.500 g F
b. 6.05 g Mg
23. a. 3.01 × 1023 atoms B
atoms Au
24. a. 80.9 g Al
25.
b. 4.068 × 1024 atoms Pb c. 1.50 × 1023 atoms Si
b. 1.51 × 1023 atoms S
b. 29.5 g Li
Particle
Electron
Proton
Neutron
c. 2.65 × 10−10 g Cl
Symbol
e−
P+
n0
c. 19.3 g N
Mass Number
0
1
1
e. 7.6 × 10−21 g W
d. 0.00112 g Br
c. 2.31 × 1022 atoms K
d. 1,590 g Au
Actual Mass
9.109 × 10−31 kg
1.673 × 10−27 kg
1.675 × 10−27 kg
e. 413 g Cu
f. 3 × 10−22 g Au
d. 7.872 × 1019 atoms Pt e. 3.06 × 1011
f. 8.24 × 109 g S
g. 0.000350 g Hg
Relative Charge
−1
+1
0
26. a. Since one carbon—12 atom has a mass of exactly 12 amu, then one amu will be exactly  the mass of one carbon—12
atom. b. The mass of an atom as it compares to the mass of a carbon—12 atom.
27. a. central part of an atom which contains most of the atom’s mass
b. Ernest Rutherford
28. a. 1.00 mol Ca
g. 37.4 mol Zn
e. 0.0474 mol Fe
b. 0.500 mol Na c. 0.100 mol Ni
h. 8.30 × 10−23 mol Ba
d. 4.7 mol S
c. protons & neutrons
f. 6.95 × 10−5 mol Ag
29. The law of multiple proportions states that two or more compounds composed of the same two elements, then the ratio of
the masses of the second element combined with a certain mass of the first element is always a ratio of small whole
numbers. CO & CO2, H2O & H2O2, FeO & Fe2O3, N2O5 & N2O, and CuCl & CuCl2 are examples.
30. a. 144 amu
b. 6 amu
31. An electron is a small, subatomic particle with a very small mass, a negative charge, and located within the electron cloud
on the outside of the atom far away from the nucleus.