Chapter 3
Applying Your Knowledge- Even Numbered
2.
Elements in a specific compound are always present in a definite proportion by mass; for
example, in methane, CH4, 12 g of carbon are combined with 4 g of hydrogen.
4.
Experiments indicated that matter was conserved. Elements had been identified.
Compounds had been shown to be composed of definite amounts of specific elements.
The composition of a compound had been shown to always be the same regardless of its
source. The composition of a combination of elements could be predicted.
6.
The alpha particle was deflected by something relatively large and positive called the
nucleus.
8.
Particles smaller than the atom, such as protons, neutrons, electrons.
10.
Atoms exist with 1, 2, ..., up to 116 protons; each number of protons corresponds to a
different element. Most elements exist as naturally-occurring isotopes, i.e. atoms with
various numbers of neutrons for a given number of protons. This accounts for the large
number of different masses for actual atoms. For example carbon has three different
isotopes; 12C, 13C and 14C.
12.
a. 50Ti and 50V are different elements with the same mass number; they are not isotopes.
b. 12C and 14C are isotopes with same proton count (6 each) but with different neutron
counts (6 neutrons in 12C and 8 neutrons in 14C).
c. 40Ar and 40Kr are not isotopes; Ar and Kr are different elements. They have different
numbers of protons.
14.
(a) an isotope with two fewer neutrons (20 versus 18); the isotope is the same element and
has the same number of protons (17) and electrons (17).
16.
Iodine is represented by the symbol 53 I ; it has 53 protons and 74 neutrons. The neutron
count equals the mass number minus the atomic number. 127 - 53 = 74 neutrons.
18.
In neutral atoms the number of electrons will equal the number of protons. The atomic
number equals the number of protons. The mass number equals the sum of the number of
protons and the number of neutrons.
127
a.
b.
c.
d.
e.
20.
Number of
protons
32
14
28
48
77
Number of
neutrons
41
14
31
64
115
Number of
electrons
32
14
28
48
77
Atomic
number
32
14
28
48
77
Mass
number
73
28
59
112
192
Atomic number or number of protons. This is the quantity that determines the nature of
the nucleus. Isotopes have different neutron amounts but the same proton count.
6
22.
Isotope
Bromine-81
Boron-11
Chlorine-35
Chromium-52
Nickel-60
Strontium-90
Lead-206
24.
Atomic No.
35
5
17
24
28
38
82
Mass No. No.of protons
81
35
11
5
35
17
52
24
60
28
90
38
206
82
No. of neutrons
46
6
18
28
32
52
124
No. of electrons
35
5
17
24
28
38
82
The symbol for krypton is Kr. The atomic number for Kr is 36. The average atomic weight
for krypton is 83.80 amu. The electron arrangement has to account for 36 electrons;
2-8-18-8. Much of this information can be taken from the entry for krypton in the
periodic table.
36
Atomic number
Element symbol
Kr
83.80
Average atomic weight
26.
(a) 350 x 10-7 cm (students need to do the math)
28.
(b) 2n2 for example, n=1 has 2 electrons, n=2 has 8 electrons, n=3 has 18 electrons etc.
30.
Element
11Na
12Mg
13Al
14Si
32.
Ultraviolet light has wavelengths in the range 190 nm to 400 nm. The frequency can be
c
calculated from the wavelength, 200 nm, using the formula ν= . Where the speed of light,
λ
8
3
x
10
m/s
c, is 3.0 x 108 m/s. ν = [
] ÷ [( 200 nm)] = (3.0 x 108 m/s) ÷ (2 .x 10–7 m)
1
ν = 1.5 x 1015 cycles/s = 2 x 1015 Hertz. The units for frequency are Hertz or cycles/s.
The answer is rounded to 1 significant figure.
34.
a. A group or family is a vertical column in the periodic table.
b. A period is a horizontal row in the periodic table.
c. Chemical properties of an element describe its reactivity with other elements and
compounds.
d. Transition elements are elements in the "B" groups, starting with group IIIB and
ending with IIB.
e. Inner transition elements are the rows of elements between lanthanum and hafnium
and between actinium and Rutherfordium; elements 58-71 and 90-103.
f. Representative elements are main-group elements in the "A" groups; groups IA and
IIA, IIIA through VIIIA.
Bohr electron arrangement
2-8-1
2-8-2
2-8-3
2-8-4
Element
15P
16S
17Cl
18Ar
7
Bohr electron arrangement
2-8-5
2-8-6
2-8-7
2-8-8
36.
Metals are on the left side and bottom of the periodic table. Nonmetals are in the
upper right corner of the table, as you view the table. Metalloids are the eight elements
between metals and nonmetals.
metals
nonmetals
metalloids
H
Li Be
Na Mg
K
Ca Sc
Ti
V
M
Fe
Co
Ni
Cu Zn
Rb
Cs
Fr
Zr
Hf
*
Nb Mo Tc
Ta W Re
Ru
Os
Rh
Ir
Pd
Pt
Ag Cd In
Au Hg Tl
Sr
Ba
Ra
Y
La
Ac
Cr
B
Al
Ga
C
N
Si P
Ge As
O
S
Se
F
Cl
Br
He
Ne
Ar
Kr
Sb
Bi
Te
Po
I
At
Xe
Rn
Sn
Pb
* The remaining elements are metals.
38.
a.
c.
e.
Nitrogen, nonmetal
Argon, nonmetal
Uranium, metal
40.
All of the alkali metals Li, Na, K, Rb, Cs, and Fr have one valence electron.
42.
a.
b.
c.
d.
e.
f.
44.
The Lewis symbol can be determined by locating the element in the periodic table and
identifying the group number. For example, Beryllium is in Group IIA. It has two valence
electrons and two dots in the Lewis symbol. Similarly Potassium has one valence electron
and one dot.
Barium, Ba, is in Group IIA and has 2 valence electrons.
Aluminum, Al, is in Group IIIA and has 3 valence electrons.
Phosphorus, P, is in Group VA and has 5 valence electrons.
Selenium, Se, is in Group VIA and has 6 valence electrons.
Bromine, Br, is in Group VIIA and has 7 valence electrons.
Potassium, K, is in Group IA and has 1 valence electron.
K
46.
b.Arsenic, metalloid
d.
Calcium, metal
Be
Cl
As
Kr
a. Li is more metallic than F, fluorine. When elements are in the same row or period the
ones to the right of the periodic table are less metallic.
b. Cs is more metallic than lithium. When elements are in the same group the elements at
the bottom of a group are more metallic. They have larger atoms and lose electrons
more readily.
c. Ba Same reason as "b" above.
d. Pb Same reason as "b" above.
e. Al Same reason as "b" above.
f. Na Same reason as "a" above.
8
48.
a.
b.
c.
d.
e.
f.
g.
48
33
mass number = 46 neutrons + 35 protons = 81
56
30
38 protons and 50 neutrons
Indium, thallium, and aluminum form compounds similar to those formed by Ga.
50.
The smallest member of a group typically is at the top of the group. F, Cl, Br, I, At
52.
Reactivity of metals increases with increasing atomic radius. The outer electrons are not
bound to the nucleus as tightly.
54.
The larger of two atoms is typically more reactive for metals and the smaller is more
reactive for nonmetals. Metal atoms at the top of a group are smaller and less reactive,
metals lose electrons. Removing an electron is more difficult for small atoms. Nonmetal
atoms at the top of a group are smaller than those at the bottom and are more reactive
than atoms at the bottom. The nonmetals gain electrons. The smaller the nonmetal the
stronger the attraction for an additional electron. Noble gases are generally less reactive
than other atoms. Note below that in "e" xenon is more like a metal than helium is.
a. Rb more reactive than Li
b. Ba more reactive than Mg
c. Na more reactive than Ar
d. O more reactive than Ne
e. Xe more reactive than He
f. F more reactive than Br
56.
a. Atomic size generally decreases left to right across a row or period. For example here
are the relative atomic radii for period 2
Li
Be
B
C
N
O
F
Ne
b. Atomic size generally increases from top to bottom in a group. For example here are
the relative atomic radii for Group IA.
Li
Na
K
Rb
9
Cs
58.
The elements Fr, Ra, Po, At, and Rn are all at the bottom of their respective groups.
For these five elements predict the most metallic, most nonmetallic, largest atomic radius,
least reactive, and which reacts most vigorously with water.
a. Fr, most metallic
c. Fr, largest atomc radius
e. Fr, react most readily with water
b. At, most nonmetallic
d. Rn most unreactive
60.
Both oxygen and sulfur have 6 outer electrons. Both form negative ions by gaining two
electrons. The ions are oxide, O2-, and sulfide, S2-. The ions are formed when the atoms
gain two electrons to complete the octets of the atoms. The sulfur and oxygen atoms
usually form two covalent bonds. The hydrides are H2O and H2S.
62.
The time requires for the photon any distance can be calculated using the general
relationship, time = distance / speed. Here the 24,000 mile distance needs to be converted
to meters.
time = (24,000 miles ) (1000 m/0.62 mile) ÷(3.0 x 108 m/s) = 0.13 s
64.
(b) mass and matter; molecules. Based on the law of mass conservation and that elements
on each side of the equation remain the same but are rearranged during a chemical
reaction.
10