Summer Assignment Chapter 2
PROBLEMS pg. 69 #7, 11, 13, 15, 17, 20, 21, 22, 27, 28, 30, 31, 33, 35, 38, 40, 41, 43, 45, 47, 49, 55, 56, 57, 58,
60, 61, 64, 67, 69, 71, 87
7
The diameter of a neutral helium atom = 1 × 102 pm. Suppose that we could line up helium
atoms side by side in contact with one another. Approximately how many atoms would it take
to make the distance from end to end 1 cm?
0.01 m
1 pm
First, convert 1 cm to picometers.
1 cm ×
×
= 1 × 1010 pm
−12
1 cm
1 × 10 m
? He atoms = (1 × 1010 pm) ×
1 He atom
= 1 × 108 He atoms
2
1 × 10 pm
11
What do we call atoms of the same elements with different mass numbers? Isotopes.
13
What is the mass number of an iron atom that has 28 neutrons?
For iron, the atomic number Z is 26. Therefore the mass number A is:
15
For the following atoms, determine the number of protons and neutrons.
3
4
48
24
25
79
195
Isotope
12 Mg
12 Mg
35 Br
78 Pt
2 He
2 He
22Ti
No. Protons
2
2
12
12
22
35
78
No. Neutrons
1
2
12
13
26
44
117
17
Give the symbol for the following isotopes:
23
(a) Z= 11 A = 23
(b)
Z= 28 A = 64
11 Na
A = 26 + 28 = 54
64
28
Ni
20
State two differences between a metal and a nonmetal.
Metals conduct heat and electricity, are shiny & malleable; nonmetals are poor conductors, generally dull
and brittle.
21
Write the names and symbols for four elements in each of the following categories:
(a) nonemetal: phosphorous P, bromine Br, neon, Ne, carbon C
(b) metal: iron Fe, cesium Cs, iridium, Ir, praseodymium Pr
(c) metalloid: silicon Si, germanium Ge, boron B, antimony Sb
22
Define, with two examples, the following terms:
(a) Alkali metals: (1st column) Sodium, rubidium;
(b) alkaline earth metals: (2nd column) barium, beryllium;
(c) halogens: (7th column) fluorine, iodine;
(d) noble gases: (8th column) xenon, krypton
27
What is the difference between an atom and a molecule?
An atom is the smallest representative unit of an element.
A molecule is the smallest representative unit of a (non-ionic) compound, composed of two or more
atoms chemically bonded.
28
What are allotropes? Allotropes are different physical forms of the same element.
Examples? graphite and diamond are two allotropes of carbon.
2
SUMMER ASSINGMENT ANSWER KEY: CHAPTER 2
How are allotropes different from isotopes?
Allotropes refer to differences in physical form of a macroscopic sample of an element. Isotopes refer
to differences between individual atoms of an element.
30
Give an example of each of the following:
(a) a monatomic cation: Many possibilities: Na+, Ba2+, Fe3+, etc.
(b) a monatomic anion: Many possibilities: Cl–, O2–, etc.
(c) a polyatomic cation: NH4+, Hg22+
(d) a polyatomic anion: Many possibilities: NO3–, SO42–, PO43–, etc.
33
Elements:
N2 , S 8 , H 2
Compounds: NH3, NO, CO, CO2, SO2
35
Ion
No. protons
No. electrons
38
The molecular formula shows the exact number of atoms of each element in the smallest unit of a
substance (a molecule), while an empirical formula indicates the simplest whole-number ratio of each
element in a substance.
Na+
11
10
Ca2+
20
18
Al3+
13
10
Fe2+
26
24
I–
53
54
F–
9
10
S2–
16
18
O2–
8
10
N3–
7
10
What are similarities and differences between empirical formula ad molecular formula? They are
similar in that the ratio of one element to another is the same in either formula for a given substance,
while they are different in that the empirical formula will not necessarily indicate the actual number of
atoms of the elements in a substance.
40
What does P4 signify? The formula P4 signifies a molecule that contains 4 phosphorous atoms. How
does it differ from 4 P? The term 4P indicates four individual, unbonded phosphorous atoms.
41
What is an ionic compound? An ionic compound is composed of cations and anions held together by
electrostatic attraction.
How is electrical neutrality maintained in an ionic compound?
Charge neutrality is maintained by having ions present in the reverse ratio of the magnitude of their
charges.
43
What are the empirical formulas of the following compounds?
(a) C2N2
CN
(b) C6H6
CH
(c) C9H20
C9H20
(d) P4O10
P2O5
(e) B2H6
BH3
SUMMER ASSINGMENT ANSWER KEY: CHAPTER 1 – CHAPTER 2
45
3
Write the molecular formula of glycine, shown below:
In organic compounds, carbon is generally listed first, then hydrogen, then the other elements by
increasing atomic number. Thus we have C2H5NO2. A more descriptive formula is the structural
formula, grouping atoms together by their bonding arrangement: NH2CH2COOH.
47
Which of the following compounds are likely to be ionic? Which are likely to be molecular?
Compounds of metals with nonmetals are usually ionic. Nonmetal-nonmetal compounds are usually
molecular.
Ionic:
LiF, BaCl2, KCl
Molecular:
SiCl4, B2H6, C2H4
49
What is the difference between inorganic and organic compounds?
The difference between inorganic compounds and organic compounds is that organic compounds
contain carbon in combination with hydrogen, oxygen, nitrogen, and/or sulfur. All other compounds
are considered inorganic.
55
(a)
(b)
(c)
(d)
(e)
(f)
(g)
(h)
56
(a) KClO: This is an ionic compound in which the metal cation (K+) has only one charge. The correct
name is potassium hypochlorite. Hypochlorite is a polyatomic ion with one less O atom than the
chlorite ion, ClO2–
KH2PO4: potassium dihydrogen phosphate
(i) PF5: phosphorus pentafluoride
K2HPO4: potassium hydrogen phosphate
(j) P4O6: tetraphosphorus hexoxide
HBr (gas) : hydrogen bromide (molecular compound)
HBr (in water): hydrobromic acid (aqueous solution)
Li2CO3: lithium carbonate
(k) CdI2: cadmium iodide
K2C2O7: potassium dichromate
(l) SrSO4: strontium sulfate
NH4NO2: ammonium nitrite
(m) Al(OH)3: aluminum hydroxide
HIO3: iodic acid
(b) Ag2CO3: silver carbonate. Silver can form only the +1 ion, so the Roman numeral is not needed.
Other single-charge transition metals are Cd and Zn, forming the 2+ ions Cd2+ and Zn2+.
(c) HNO2: This is an oxoacid that contains the nitrite ion, NO2–. The “-ite” suffix is changed to
“-ous”. The correct name is nitrous acid.
(d) KMnO4: potassium permanganate
(e) CsClO3: cesium chlorate
(f) KNH4SO4: potassium ammonium sulfate
4
SUMMER ASSINGMENT ANSWER KEY: CHAPTER 2
(g) FeO: This is an ionic compound in which the metal can form more than one cation. Use a Roman
numeral to specify the charge of the Fe ion. Since the oxide ion has a −2 charge, the Fe ion has a
+2 charge. The correct name is iron(II) oxide.
(h) Fe2O3: iron(III) oxide
(i) TiCl4: This is an ionic compound in which the metal can form more than one cation. Use a Roman
numeral to specify the charge of the Ti ion. Since each of the four chloride ions has a −1 charge
(total of −4), the Ti ion has a +4 charge. The correct name is titanium(IV) chloride.
(j) NaH: sodium hydride
(k) Li3N: lithium nitride
(l) Na2O: sodium oxide
(m) Na2O2: This is an ionic compound in which the metal cation (Na+) has only one charge. The O22–
ion is called the peroxide ion. Each oxygen has a −1 charge. You can determine that each oxygen
only has a −1 charge, because each of the two Na ions has a +1 charge. Compare this to sodium
oxide in part (l). The correct name is sodium peroxide.
57
(a)
(b)
(c)
(d)
(e)
rubidium nitrite: RbNO2
potassium sulfide: K2S
sodium hydrogen sulfide: NaHS
magnesium phosphate: Mg3(PO4)2
calcium hydrogen phosphate: CaHPO4
(f)
(g)
(h)
(i)
(j)
potassium dihydrogen phosphate: KH2PO4
iodine heptafluoride: IF7
ammonium sulfate: (NH4)2SO4
silver perchlorate: AgClO4
boron trichloride: BCl3
58
(a) copper(I) cyanide: The Roman numeral I tells you that the Cu cation has a +1 charge. Cyanide
has a −1 charge. Since, the charges are numerically equal, no subscripts are necessary in the
formula. The correct formula is CuCN.
(b) strontium chlorite: Strontium is an alkaline earth metal. It only forms a +2 cation. The
polyatomic ion chlorite, ClO2–, has a −1 charge. Since the charges on the cation and anion are
numerically different, the subscript of the cation is numerically equal to the charge on the anion,
and the subscript of the anion is numerically equal to the charge on the cation. The correct
formula is Sr(ClO2)2.
(c) perbromic acid: Perbromic tells you that the anion of this oxoacid is perbromate, BrO4–. The
correct formula is HBrO4(aq). Remember that (aq) means that the substance is dissolved in water.
(d) hydroiodic acid: Hydroiodic tells you that the anion of this binary acid is iodide, I–. The correct
formula is HI(aq).
(e) disodium ammonium phosphate: Na is an alkali metal. It only forms a +1 cation. The
polyatomic ion ammonium, NH4+, has a +1 charge and the polyatomic ion phosphate, PO43–, has a
−3 charge. To balance the charge, you need 2 Na+ cations. The correct formula is Na2(NH4)PO4.
(f) lead(II) carbonate: The Roman numeral II tells you that the Pb cation has a +2 charge. The
polyatomic ion carbonate, CO32–, has a −2 charge. Since, the charges are numerically equal, no
subscripts are necessary in the formula. The correct formula is PbCO3.
(g) tin(II) fluoride: The Roman numeral II tells you that the Sn cation has a +2 charge. Fluoride has a
−1 charge. Since the charges on the cation and anion are numerically different, the subscript of the
cation is numerically equal to the charge on the anion, and the subscript of the anion is numerically
equal to the charge on the cation. The correct formula is SnF2.
SUMMER ASSINGMENT ANSWER KEY: CHAPTER 1 – CHAPTER 2
5
(h) tetraphosphorous decasulfide: This is a molecular compound. The Greek prefixes tell you the
number of each type of atom in the molecule. The correct formula is P4S10.
(i) mercury(II) oxide: The Roman numeral II tells you that the Hg cation has a +2 charge. Oxide has
a −2 charge. Since, the charges are numerically equal, no subscripts are necessary in the formula.
The correct formula is HgO.
(j) mercury(I) iodide: The Roman numeral I tells you that the Hg cation has a +1 charge. However,
this cation exists as Hg22+. Iodide has a −1 charge. You need two iodide ion to balance the +2
charge of Hg22+. The correct formula is Hg2I2.
(k) selenium hexafluoride: This is a molecular compound. The Greek prefixes tell you the number
of each type of atom in the molecule. The correct formula is SeF6.
60
Which one in each pair resembles each other most closely in chemical properties?
𝑎) !!H 𝑎𝑛𝑑 1 H
1
+
b)
14
7
N and
14
7
N 3−
c)
12
6
C and 136 C
Changing the electrical charge of an atom usually has a major effect on its chemical properties
The two electrically neutral carbon isotopes should have nearly identical chemical properties.
61
One isotope of a metallic element has mass number 65 and 35 neutrons in the nucleus. The
cation derived from the isotope has 28 electrons. Write the symbol for this cation.
The number of protons = 65 − 35 = 30. The element that contains 30 protons is zinc, Zn. There are
two fewer electrons than protons, so the charge of the cation is +2. The symbol for this cation is Zn2+.
64
What is wrong with or ambiguous about the phrase “four molecules of NaCl”?
NaCl is an ionic compound; it doesn’t form molecules.
67
What is wrong with the name in parentheses?
(a) BaCl2 (barium dichloride) This is an ionic compound. Prefixes are not used. The correct name is
barium chloride.
(b) Fe2O3 [iron(II) oxide] Iron has a +3 charge in this compound. The correct name is iron(III)
oxide.
(c) CsNO2 (cesium nitrate) NO2− is the nitrite ion. The correct name is cesium nitrite.
(d) Mg(HCO3)2 [magnesium(II) bicarbonate] Magnesium is an alkaline earth metal, which always
has a +2 charge in ionic compounds. The Roman numeral is not necessary. The correct name is
magnesium bicarbonate. Note: bicarbonate is the old nomenclature. Modern nomenclature would
be magnesium hydrogen carbonate.
69
Fill in the blanks in the following table:
11
54
2+
31 3−
196
Symbol
5B
26 Fe
15 P
79 Au
Protons
5
26
15
79
Neutrons
6
28
16
117
Electrons
5
24
18
79
Net Charge 0
0
+2
−3
71
222
86
Rn
86
136
86
0
Write the formula of the common ion derived from each of the following:
(a) Li+, alkali metals always have a +1 charge in ionic compounds
(b) S2–
(c) I–, halogens have a −1 charge in ionic compounds
(d) N3–
6
SUMMER ASSINGMENT ANSWER KEY: CHAPTER 2
(e) Al3+, aluminum always has a +3 charge in ionic compounds
(f) Cs+, alkali metals always have a +1 charge in ionic compounds
(g) Mg2+, alkaline earth metals always have a +2 charge in ionic compounds.
87
alkali
metals
alkaline
earth metals
noble gases
halogens
1A
8A
2A
The metalloids are shown in gray.
3A 4A 5A 6A 7A