Chemistry
Section
_____
_____________________________
Name:
Chapter 4 WS Key
Date:
________________________
A. Multiple Choice
1. The number of protons in the nucleus of carbon-13 is
a. 19
b. 13
c. 7
d. 6
2. The atomic mass unit is defined by the mass of an atom of:
a. 11B
b. 12C
c. 23Na
d.
24
Mg
3. The atomic number of an atom is always equal to the total number of:
a. neutrons in the nucleus
c. neutrons plus protons in the atom
b. protons in the nucleus
d. protons plus electrons in the atom
4. Which two particles have approximately the same mass?
a. neutron and electron
c. proton and neutron
b. neutron and deuteron
d. proton and electron
5. The existence of fractional atomic masses is best explained by the
a. mass of electrons
b. existence of isotopes
c. inaccuracies in determining atomic masses
d. varying number of protons in the nucleus of atoms
6. Which pair of atoms are isotopes?
a. C and N
b. K and Ar
c.
K and
K
d.
Ra and
Rn
7. Which set of particles is arranged in order of increasing mass?
a. H2, H, H+
b. H+, H, H2
c. H2, H+, H
d. H, H+, H2
8. Compared to an atom of 14C, an atom of 12C has:
a. more protons
b. fewer protons
c. more neutrons
d. fewer neutrons
9. An atom of oxygen, O, containing 10 neutrons has a mass number of
a. 8
b. 10
c. 16
d. 18
10. Isotopes of the same element DO NOT have the same
a. number of electrons
c. mass number
b. atomic number
d. electron configuration
B. Short Answer: Krypton, Kr, is element number 36 on the Periodic Table. Complete the table
below for a nuclide of krypton that has a mass number of 84.
Hyphen
Notation
Nuclear
Symbol
number of
protons (p+)
number of
electrons (e-)
number of
neutrons (n0)
krypton-84
84
36Kr
36
36
48
Created 23 October 2013
C. Word Problems: Be sure to show the formula you use and all your work for any calculations.
No credit will be given for problems that do not show your work.
1. There are only two naturally occurring nuclides of gallium: gallium-69 (68.925 581 u) and
gallium-71 (70.924 705 u). If the relative natural abundance of gallium–69 is 60.108%,
what is the weighted average atomic mass of gallium?
Σ (nuclide mass) (decimal percent) = atomic mass
Ga: (68.925 581 u) (0.601 08) = 41.492 788 u
Ga: (70.924 705 u) (0.398 92) = 28.283 283 u
69.723 u
2. The radioactive decay of uranium–238 proceeds by alpha decay. Two gamma rays are
emitted at the same time. Write the nuclear reaction that shows this decay showing the
nuclear symbol for the alpha particle. Also, clearly identify the alpha particle.
U → He +
Th + 2γ
3. Show the six scientists discussed in class who advanced atomic theory. Name them in
correct chronological order, show the theory they suggested, and give the experiment or
logic they used to develop their theory.
Democritus
Aristotle
John Dalton
400 BC
350 BC
1808 AD
atomos – smallest particle
hyle – continuous matter
billiard ball – indivisible,
smallest particle
JJ Thomson
1897 AD
plum pudding – electrons
in positive pudding
mass
Robert Millikan
1910 AD
Ernest Rutheford
1911 AD
/ charge) ratio e–
(
discovered the charge of
the electron
nuclear model – small,
dense nucleus with esurrounding empty
space
none, philosophical argument
none, philosophical argument
laws of: conservation of matter
definite proportion
multiple proportion
Cathode ray tube / e- beam
(a Crookes tube)
Oil drop experiment (gravity,
e– charge, and charged plates)
α – particle / gold foil