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Summer Mini-Session 2:
Atoms and the Periodic Table
Answer Key
Isotopes and Ions Worksheet:
Electrons, Protons and Neutrons...Oh, My!!
element
symbol
# protons
# electrons
# neutrons
1. Calcium
Ca
20
20
20
2. Bromine
Br
35
35
45
3. Sodium ion
Na+
11
10
12
4. Oxide ion
O -2
8
10
8
5. Fluoride ion
F-
9
10
10
U
92
92
142
C
6
6
8
Ba
56
56
79
Fe
26
26
28
Ti
22
22
24
6. Uranium-234
234
92
14
6
7. Carbon-14
8. Barium-135
135
56
9. Iron-54
54
26
10. Titanium-46
46
22
For each of the following elements, calculate the average mass to two decimal places:
11.
10.80
Boron: 20% Boron-10, 80% Boron-11
12.
47.92
Titanium: 8.25% Titanium-46, 7.44% Titanium-47, 73.72% Titanium-48,
5.41% Titanium-49, 5.18% Titanium-50
13.
24.32
Magnesium: 79% Magnesium-24, 10% Magnesium-25, 11% Magnesium-26
14.
12.01
Carbon: 98.89% Carbon-12, 1.11% Carbon-13
15.
35.48
Chlorine: 75.77% Chlorine-35, 24.23% Chlorine-37
Chpt. 3, Sect. 2 #3, 5
3.
Subatomic
Particle
Mass
Charge
Location
proton
1 amu
positive
nucleus
neutron
1 amu
neutral
nucleus
electron
0.0005 amu
negative
cloud around nucleus
5. The nucleus is composed of neutrons and protons. Protons have a positive charge.
Positive charges should repel each other causing the nucleus to fly apart,
therefore there must be some sort of force (a nuclear force) keeping the nucleus
together despite the repulsion of like electrostatic charges.
Chpt. 3, Sect. 3 #2, 3
2. a. protons - 11, electrons - 11, neutrons - 12
b. protons - 20, electrons - 20, neutrons - 20
c. protons - 29, electrons - 29, neutrons - 35
d. protons - 47, electrons - 47, neutrons - 61
3. a.
28
14
Si
Silicon - 28
b.
56
26
Fe
Iron - 56
Chpt. 3 Review
#5-12, 19, 25, 27
5. Rutherford described the atom as consisting mostly of empty space and having a
small but extremely dense positive center (the nucleus). He came to this
conclusion after firing alpha particles at a thin sheet of gold foil. The majority of
the particles passed right through the foil as if there were nothing there (the
atom is mostliy empty space). However, a few particles “bounced” back as if
encountering a very dense/massive positively charged particle (the nucleus).
6. The atomic number uniquely identifies an element.
Chpt. 3 Review
#5-12, 19, 25, 27 (cont.)
7. a. Isotopes are different “versions” or “flavors” of an element that have a
different atomic mass from each other.
b. All the isotopes of a particular element will have the same number of protons,
and virtually identical properties.
c. Each isotope will have a different number of neutrons from the others (this is
why they have different atomic masses).
8.
Isotope
Number of
protons
Number of
electrons
Number of
neutrons
Si-28
14
14
14
Si-29
14
14
15
Si-30
14
14
16
9. a. The atomic number of an element describes the number of protons that every
atom of that element has.
b. The mass number of an isotope describes the atomic mass for an atom of that
particular isotope. The number can be calculated by adding the number of
protons and the number of electrons together.
c. The mass number, “2", is found superscript left in the symbol for deuterium.
The atomic number, “1", is listed subscript left.
10. A nuclide is a term used to refer to a specific isotope of an element.
11. a. Helium-4
b. Oxygen-16
c. Potassium-39
12. a. Carbon-12 is the nuclide used as the standard for relative mass.
b. It’s assigned atomic mass is exactly 12 amu.
19. 0.00337 · 35.97 + 0.00063 · 37.96 + 0.99600 · 39.96 = 39.9452937 = 39.95 amu
Chpt. 3 Review
#5-12, 19, 25, 27 (cont.)
25.
Subatomic
Particle
Symbol
Mass number
Actual mass
(kg)
Relative
Charge
electron
e–
0
9.109x10 -31
-1
proton
p+
1
1.673x10 -27
1
neutron
n0
1
1.675x10 -27
0
27. a. The nucleus is the dense, positive center of the atom.
b. Ernest Rutherford (and his colleagues Geiger and Marsden) are credited with
discovering the atomic nucleus.
c. The nucleus is composed of protons and neutrons.
Chpt. 1, Sect. 3 #1-4
1. Oxygen, sulfur, copper, and silver
2. Fe, N, Ca, Hg
3. Elements in the same group are more likely to undergo similar reactions.
4. Metals tend to be shiny or have luster, be ductile and malleable, and are good
conductors of heat and electricity. Non-metals tend to be dull, brittle, and are
poor conductors of heat or electricity. Metalloids are not as malleable as metals,
but not as brittle as non-metals. Metalloids conduct electricity somewhere
between metals and non-metals and are called “semi-conductors”.
Chpt. 5, Sect. 1 #1, 3, 5
1. a. Stanislao Cannizzaro is credited with developing the method that led to
determination of standard atomic masses.
b. Dmitri Mendeleev proposed the idea that when the elements are arranged in
order, similar physical and chemical properties will be repeated periodically.
Chpt. 5, Sect. 1 #1, 3, 5 (cont.)
1. c. Henry Mosely noticed that arranging the elements by their atomic numbers
rather than by their masses caused them to match the repeating patterns of
physical and chemical properties more closely.
3. The noble gases, the Lanthanide series, and the Actinide series were all added
after Mendeleev’s original table was created.
5. There are a number of cases in the periodic table where the next highest element
is actually lighter than the preceding element. This occurs because even though
the next highest element may have an additional proton, it has less neutrons and is
therefore lighter than the preceding element. The periodic table could just as
easily be organized by mass as number of protons, BUT the physical and chemical
properties within groups/families (columns) match each other better when the
table is organized by number of protons.
Chpt. 5, Sect. 2 #1, 2, 6
1. One way to subdivide the periodic table is by blacks according to the electron
structure of the outermost layer of electrons. The four blocks are named: s, p, d,
and f blocks.
2. a.
b.
c.
d.
e.
Group 1 is called the alkali metals.
Group 2 is known as the alkaline earth metals.
Groups 3-12 are named the transition elements.
Group 17 is called the halogens.
Group 18 is known as the noble gases.
6. A hypothetical element with the atomic number 120 would belong to the group the
alkaline earth metals. However, there are two problems wrong with this question:
a) The question states “assuming it does not radioactively decay”, but it would most
likely decay since all the known elements above number 83 are known to be
radioactive.
b) The question also says “If a hypothetical element in the ‘g’ block had an atomic
number of 120", but an element with the number 120 would actually be in the “s”
block.
Chpt. 5 Review
#1, 5, 11, 22-23, 28-29, 32-34, 36, 38, 40, 44-45, 47-48
1. a. Stanislao Cannizzaro is credited with developing the method that led to
determination of standard atomic masses.
b. Dmitri Mendeleev proposed the idea that when the elements are arranged in
order, similar physical and chemical properties will be repeated periodically.
c. Henry Mosely noticed that arranging the elements by their atomic numbers
rather than by their masses caused them to match the repeating patterns of
physical and chemical properties more closely.
5. The length of any given period on the periodic table is determined by when the
outer eight valence electrons have been filled -- that is, when all the sublevels of
that period have been filled.
11. The d-block elements are referred to as “the transition elements”.
22. a. Atomic radius is the distance from the center of the atom to the outside of the
electron cloud. In simplest terms, we can think of radius as the “size” of the
atom, since the volume varies with the radius cubed.
b. Going across a period, the trend for the radius is to get smaller as you go to the
right.
c. The atomic radius gets smaller as you go across a period to the right because
the increased numbers of protons (positive charges) exerts an attractive force
on the electrons (negative charges) and pulls them in closer to the center of
the atom.
23. a. As you go down a group/family, the atomic radii of the atoms increase in size.
b. The atomic radii increase as you go down a group because for each period you go
down, you’re adding a new layer or shell of electrons.
28. a. Valence electrons are the electrons surrounding an atom that are available to
interact with other atoms. They’re the electrons that are most easily lost,
gained, added to, or shared with other atoms.
b. Valence electrons are usually located in the unfilled outer energy level or cloud
of an atom.
29. a. Group 1 typically loses 1 electron.
b. Group 2 usually loses 2 electrons.
c. Group 13 would usually lose 3 electrons.
d. Group 16 would gain 2 electrons.
e. Group 17 gains 1 electron usually.
f. Group 18 doesn’t gain or lose.
Chpt. 5 Review (cont.)
32. Between cesium, hafnium, and gold, gold should have the smallest radius. They’re
all in the same period, so none of them has any extra layers or levels of electrons
compared to the others. Gold, however, has more protons in its nucleus and more
electrons in that outer layer than either of the other two, and the increased
attraction between those extra protons and electrons will pull the electron cloud in
closer to the nucleus.
33. a. The first ionization energy is the amount of energy required to completely pull
an electron away from its neutral atom creating a +1 ion. The second ionization
energy would be the energy to now pull off a second electron, and similarly for
the third ionization energy.
b. Successive ionizations take more and more energy – the second energy will be
higher than the first, and the third ionization energy will be higher than either
of the previous two.
c. It gets harder and harder to pull additional electrons away from the atom
because the electrons have a negative charge, and the atom becomes more and
more positively charged as you remove electrons, making the electrostatic force
become successively greater with each electron you remove.
34. The following elements are listed in order of decreasing electron affinity: F, O, C,
Li, Na, Rb
36. a. K2+ is the least likely cation to form. Taking a second electron away from
potassium requires a LOT of energy.
b. All of these anions form relatively easily. Chlorine has the highest electron
affinity, so Cl - would form the easiest, then the fluoride ion, and lastly an
oxygen ion with only one negative charge. After that, the oxygen would have to
add a second electron. So, the oxide ion would be the least likely of the group.
38. Two factors affect radius: the number of shells/layers of electrons, and the
attraction between the nucleus and the surrounding cloud of electrons. They both
have an electron configuration equivalent to argon, so they’re both in the same
period as far as their electrons go. This means we don’t have to worry about which
one has more “layers” or shells of electrons. Ca2+ has a greater positive charge
than K+ and it has more protons in the nucleus. So, the electrons will be attracted
more to the calcium nucleus making the calcium ion the smaller radius.
40. a. The elements in group 18 are called the noble gases.
b. Noble gases have a complete outer shell of electrons, therefor, they neither
want to gain nor lose any electrons making them extremely nonreactive.
Chpt. 5 Review (cont.)
44. a. Fluorine is a hologen. It has the highest electronegativity on the table and is
extremely reactive. It is a gas at room temperature.
b. Xenon is a noble gas making it a very non-reactive substance.
c. Sodium is an alkali metal. Like fluorine, extremely reactive. So reactive, in
fact, that it’s not found in its pure form in nature. It is a silvery soft metal
with a relatively low electronegativity and electron affinity. However, sodium
has a very small atomic radius.
d. Gold is a transition metal. Metals tend to be good conductors of heat and
electricity. They tend to be ductile and malleable. They tend to be shiny or
have luster. Gold should share these properties.
45. a.
b.
c.
d.
e.
f.
g.
h.
i.
j.
Li+, noble gas configuration: helium.
Rb+, Kr
O2-, Ne
F -, Ne
Mg2+, Ne
Al3+, Ne
P3-, Ar
S2-, Ar
Br -, Kr
Ba2+, Xe
47. Halogens are 1 electron away from having a complete shell of outer electrons.
Once they gain this electron, they will have a negative one charge and a complete
shell. At that point, they will not have a high affinity for any more electrons.
48. a. Ionization energy follows this trend (increasing across the period to the right
and as you go up within a group). Electronegativity and electron affinity also
follow this trend, BUT not all the way into the noble gases.
b. Atomic radius follows this trend (increasing as you go across a period to the
left and as you go down the group).
c. None of the listed properties follow this trend.