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Chemistry Assignments
Ch 4 Atomic Structure
pg 103
4) all matter is composed of atoms
atoms of different elements differ
chemical change involves a rearrangements of atoms
5) Atoms of one element are never changed into atoms of another element
as a result of a chemical change
6) 5 x 10-2 nm to 2 x 10-1 nm
7) 1.05 x 10-22 g
pg 102
Atoms are separated, joined, or rearranged.
pg 105
Checkpoint: A negatively charged plate repels a cathode ray.
pg 108
10) proton—positive charge, relative mass = 1
electron—negative charge, relative mass = 1/1840
neutron—no charge, relative mass = 1
11) Thomson passed an electric current through sealed glass tubes filled with gases
The resulting glowing beam consisted of tiny negatively charged particles moving
at high speed. Thomson concluded that electrons must be parts of the atoms of
all elements. Millikan determined the charge and mass of the electron.
12) Rutherford expected all the alpha particles to pass straight through, but some
particles were deflected at very large angles—and some even bounced straight back.
13) The great majority of the alpha particles passed straight through the gold foil.
14) Rutherford’s atomic model described the atom as having a positively charged, dense
nucleus that is tiny compared to the atom as a whole. In Thomson’s plum pudding
model, electrons were stuck in a chunk of positive charge.
pg 111
Checkpoint: Mass number = number of neutrons + atomic number
15) a) 19
b) B
c) 5
d) 5
e) 16
f)16
16) a) 9 protons and 9 electrons
b) 20 protons and 20 electrons
c) 13 protons and 13 electrons
pg 112
17) a) 8
b) 16
c) 61
d) 45
e) 125
g)23
h) 23
18) a) C, mass number = 12, atomic number = 6
b) F, mass number = 19, atomic number = 9
c) Be, mass number = 9, atomic number = 4
pg 113
Checkpoint: hydrogen-1, hydrogen-2, hydrogen-3
19) oxygen, O with atomic number 8 and mass numbers 16, 17, 18
20) Chromium-50 has 26 neutrons
Chromium-52 has 28 neutrons
Chromium 53 has 29 neutrons
pg 111
Checkpoint: Add the number of neutrons and number of protons (atomic number)
pg 113
Checkpoint: hydrogen-1 (protium), hydrogen-2 (deuterium), hydrogen-3 (tritium)
pg 116
Checkpoint: The number of stable isotopes, the mass of each isotope,
and the natural abundance (expressed as a percent)
of each isotope.
pg 117
23) 63.6 amu
24) 79.91 amu
pg 119
30) 194 represents the mass number
31) The atomic mass is the weighted average of the masses of its isotopes
32) a) lithium-6: 3p+, 3e-, 3no; lithium-7: 3p+, 3e-, 4no;
b) calcium-42: 20p+, 20e-, 22no; calcium-44: 20p+, 20e-, 24no;
c) selenium-78: 34p+, 34e-, 44no; selenium-80: 34p+, 34e-, 46no;
33) any two: beryllium (Be), magnesium (Mg), strontium (Sr), barium (Ba), radium (Ra)
Elements Handbook: oxygen (Period2, Group 6A)
carbon (Period 2, Group 4A)
hydrogen (Period 1, Group 1A)
nitrogen (Period 2, Group 5A)
calcium (Period 4, Group 2A)
pg 122
35) Democritus’ ideas were not helpful in explaining chemical behavior because
they lacked experimental support.
36) Dalton would agree with all four statements because they all fit his atomic theory.
38) a) A beam of electrons (cathode rays) is deflected by an electric field toward the
positively charged plate.
b) The cathode rays were always composed of electrons regardless of the metal
used in the electrodes or the gas used in the cathode-ray tube.
39) repel
40) The mass of the proton and neutron are equal; protons are positively charged and
neutrons are neutral.
42) The electrons were stuck in a lump of positive charge.
44) positive
45) protons and neutrons (Rutherford suspected there was something in the nucleus in
addition to protons—but didn’t know them as neutrons)
46) It has equal numbers of protons and electrons.
48) a) 15
b) 42
c) 13
d) 48
e) 24
f) 82
50) a) 19
b) 9
c) F
d) 14
e) 29
f) Si
h) 22
i) Ti
j) 25
k) 30
l) Mn
g) 22
52) because of the existence of isotopes
61) All atoms of the same elements are not identical (isotopes). The atoms is not
the smallest particle of matter.
68) a) 92.90 %
b) 99.89%
c) .00993%
72) Because they have identical numbers of protons, they also have identical numbers
of electrons; electrons are the subatomic particles that are responsible for
chemical behavior.
pg 125
1) C
2) A
3) B
4) B
5) 9; three Ca-42 atoms have an approximate mass of 3 x 42- 126 amu;
one N-14 atoms has an approximate mass of 145 amu;
126/14 = 9 N-14 atoms with an approximate mass of 126 amu.
6) E
7) false, true
8) true, false
9) true, true, correct explanation