, SOLUTION MANUAL FOR
Chemical Principles 9th Edition Zumdahl
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,CHAPTER 2
ATOMS, MOLECULES, AND IONS
Discussion Questions
1. When water boils, H2O(l) is converted to H2O(g). So, water vapor is present in the bubbles
(answer d). For H2(g) and O2(g) to form, a lot more energy must be added to break down water
into its elements.
2. A singular atom of any element is neither a solid nor a liquid nor a gas (statement e is correct).
Only collections of atoms can be characterized as a solid, liquid, or gas.
3. The data needed would be the mass of chalk before writing your name and the mass of chalk
after writing your name. In a separate experiment, weigh a sample of chalk that has a known
number of “chalk molecules,” then determine the mass of one “chalk molecule.” Once the mass
of a “chalk molecule” is known, one can convert the mass of chalk used to write your name into
the number of “chalk molecules.” Note that chalk is composed of the ionic compound calcium
carbonate, CaCO3. Calcium carbonate is an ionic compound composed of ions, not molecules.
This is why “chalk molecules” is put in quotation marks.
4. a. Thomson’s plum pudding model of the atom consisted of a diffuse cloud of positive charge
with the negative charged electrons embedded randomly in it. Since electrons were the
centerpiece of his model, Thomson would probably consider electrons as the most important
particle. When different atoms come together to react to form a compound, it is the electrons
that are shared or transferred to form new substances.
b. The protons are next most important. The number of protons dictates how many electrons are
required to form specific neutral atoms or charged ions, which is related to the compounds
that form.
c. Thomson applied high voltage between metal electrodes in evacuated tubes to produce a
stream of negative charged particles. Any model that explains the results of the cathode ray
experiments would be a possible answer to this question.
5. An ice cube has the H2O molecules packed very closely together. Steam consists of separate H2O
molecules with lots of space between them. Any drawing illustrating these differences between
the two states is fine. Also illustrated should be that the number and size of the H2O molecules
do not change when an ice cube is converted to steam in a closed container. Because the number
of water molecules doesn’t change, the mass will not change.
6. Assuming no substances can enter or leave the glass container, then the mass before the reaction
should be identical to the mass after the reaction. In a chemical reaction, some bonds are broken
between the atoms in the reactant compounds and some new bonds form in the product
compounds. But the number and types of atoms are the same before a reaction as compared to
after a reaction. Since atoms are conserved in a chemical reaction, mass is conserved. Answer b
is correct.
,2 CHAPTER 2 ATOMS, MOLECULES, AND IONS
7. Natural niacin and commercially produced niacin have the exact same formula of C6H5NO2.
Therefore, both sources produce niacin having an identical nutritional value. There may be other
compounds present in natural niacin that would increase the nutritional value, but the nutritional
value due to just niacin is identical to the commercially produced niacin.
8. Yes, many questions are raised from Dalton’s theory. For example, how atoms are different from
one another; how atoms are of the same element identical to each other; how atoms are held
together when in compounds; if atoms are particles, what their mass is; etc.
9. Mass is conserved in a chemical reaction because atoms are conserved. Chemical reactions
involve the reorganization of atoms, so formulas change in a chemical reaction, but the number
and types of atoms do not change. Because the atoms do not change in a chemical reaction, mass
must not change. In this equation we have two oxygen atoms and four hydrogen atoms both
before and after the reaction occurs.
10. a. Atoms have specific masses and are neither created nor destroyed by chemical reactions.
Because atoms are conserved in a chemical reaction, mass cannot change in a chemical
reaction. Mass is conserved.
b. The composition of a substance depends on the number and kinds of atoms that form it. A
certain compound always has the same number and kinds of atoms in its formula.
c. Compounds of the same elements differ only in the numbers of atoms of the elements forming
them, that is, NO, N2O, NO2.
11. Some elements exist as molecular substances. That is, hydrogen normally exists as H2 molecules,
not single hydrogen atoms. The same is true for N2, O2, F2, Cl2, etc.
12. The number of protons identifies the element and determines how many electrons are required to
balance the total positive charge from the protons. So, identity and number of electrons in the
neutral element can be determined. However, the number of neutrons cannot be determined from
just the number of protons.
13. The various elements are composed of different isotopes. For example, carbon is made up of a
mixture of 12C, 13C, and 14C isotopes, with each isotope having a different mass. The mass of
carbon listed in the periodic table is an average mass of a mixture of the various carbon isotopes.
None of the isotopes have a mass of 12.011, but a large sample of carbon behaves as if each
carbon has an average mass of 12.011. Answer a is correct.
14. The electrons are on the outside of the nucleus; these are the particles that are easiest to access.
Ions form when electrons are added or removed from an atom. Immense energy is required to
add or subtract protons or neutrons to or from a nucleus.
15. Answer b is correct; H2O consists of 2 H atoms bound to one O atom. Because a hydrogen
atom’s mass is not equivalent to the mass of an oxygen atom, answer a is false. The other
answers assume an incorrect formula for H2O.
,CHAPTER 2 ATOMS, MOLECULES, AND IONS 3
16. Barium is an alkaline earth metal. All alkaline earth metals form 2+ charge cations when in ionic
compounds. The charge for most transition metal ions is not easily deduced from its position in
the periodic table. For most transition metal compounds, the charge of the metal ion is included
in the name.
17. Calcium dichloride follows the covalent rules of nomenclature, that is, the use of di-, tri-, tetra-,
etc., to indicate number of atoms in a formula. When the metal calcium is in a compound, it
forms an ionic compound. So, we use the ionic rules, and calcium chloride is the correct name.
For ionic compounds, the charges of each ion can be predicted (generally) from the periodic
table; if the charges of the ions are known, then the formula can be deduced.
18. For each experiment, divide the larger number by the smaller. In doing so, we get:
experiment 1 X = 1.0 Y = 10.5
experiment 2 Y = 1.4 Z = 1.0
experiment 3 X = 1.0 Y = 3.5
Our assumption about formulas dictates the rest of the solution. For example, if we assume that
the formula of the compound in experiment 1 is XY and that of experiment 2 is YZ, we get
relative masses of:
X = 2.0; Y = 21; Z = 15 (= 21/1.4)
and a formula of X3Y for experiment 3 [three times as much X must be present in experiment 3
as compared to experiment 1 (10.5/3.5 = 3)].
However, if we assume the formula for experiment 2 is YZ and that of experiment 3 is XY, then
we get:
X = 2.0; Y = 7.0; Z = 5.0 (= 7.0/1.4)
and a formula of XY3 for experiment 1.
Any answer that is consistent with your initial assumptions is correct.
The answer to part d depends on which (if any) of experiments 1 and 3 have a formula of XY in
the compound. If the compound in experiment 1 has formula XY, then:
21 g XY × = 19.2 g Y (and 1.8 g X)
If the compound in experiment 3 has the XY formula, then:
21 g XY × = 16.3 g Y (and 4.7 g X)
Note that it could be that neither experiment 1 nor experiment 3 has XY as the formula.
Therefore, there is no way of knowing an absolute answer here.
,4 CHAPTER 2 ATOMS, MOLECULES, AND IONS
19. a. The smaller parts are electrons and the nucleus. The nucleus is broken down into protons and
neutrons, which can be broken down into quarks. For our purpose, electrons, neutrons, and
protons are the key smaller parts of an atom.
b. All atoms of hydrogen have 1 proton in the nucleus. Different isotopes of hydrogen have 0, 1,
or 2 neutrons in the nucleus. Because we are talking about atoms, this implies a neutral
charge, which dictates 1 electron present for all hydrogen atoms. If charged ions were
included, then different ions/atoms of H could have different numbers of electrons.
c. Hydrogen atoms always have 1 proton in the nucleus, and helium atoms always have 2
protons in the nucleus. The number of neutrons can be the same for a hydrogen atom and a
helium atom. Tritium (3H) and 4He both have 2 neutrons. Assuming neutral atoms, then the
number of electrons will be 1 for hydrogen and 2 for helium.
d. Water (H2O) is always 1 g hydrogen for every 8 g of O present, whereas H2O2 is always 1 g
hydrogen for every 16 g of O present. These are distinctly different compounds, each with its
own unique relative number and types of atoms present.
e. A chemical equation involves a reorganization of the atoms. Bonds are broken between atoms
in the reactants, and new bonds are formed in the products. However, the number and types of
atoms between reactants and products do not change. Because atoms are conserved in a
chemical reaction, mass is also conserved.
Development of the Atomic Theory
20. Law of conservation of mass: Mass is neither created nor destroyed. The total mass before a
chemical reaction always equals the total mass after a chemical reaction.
Law of definite proportion: A given compound always contains exactly the same proportion of
elements by mass. For example, water is always 1 g hydrogen for every 8 g oxygen.
Law of multiple proportions: When two elements form a series of compounds, the ratios of the
mass of the second element that combines with 1 g of the first element can always be reduced to
small whole numbers. For CO2 and CO discussed in section 2.2, the mass ratios of oxygen that
react with 1 g carbon in each compound are in a 2:1 ratio.
21. From Avogadro’s hypothesis (law), volume ratios are equal to molecule ratios at constant
temperature and pressure. Therefore, we can write a balanced equation using the volume data, Cl2
+ 5 F2 → 2 X. Two molecules of X contain 10 atoms of F and two atoms of Cl. The formula
of X is ClF5 for a balanced equation.
22. a. The composition of a substance depends on the numbers of atoms of each element making up
the compound (depends on the formula of the compound) and not on the composition of the
mixture from which it was formed.
b. Avogadro’s hypothesis (law) implies that volume ratios are proportional to molecule ratios at
constant temperature and pressure: H2 + Cl2 → 2 H Cl. From the balanced equation, the
volume of H Cl produced will be twice the volume of H 2 (or Cl2) reacted.
,CHAPTER 2 ATOMS, MOLECULES, AND IONS 5
23. Avogadro’s hypothesis (law) implies that volume ratios are equal to molecule ratios at constant
temperature and pressure. Here, 1 volume of N2 reacts with 3 volumes of H2 to produce 2 volumes
of the gaseous product or, in terms of molecule ratios,
1 N2 + 3 H2 → 2 product
For the equation to be balanced, the product must be NH3.
24. For CO and CO2, it is easiest to concentrate on the mass of oxygen that combines with 1 g of
carbon. From the formulas (two oxygen atoms per carbon atom in CO2 versus one oxygen atom
per carbon atom in CO), CO2 will have twice the mass of oxygen that combines per gram of carbon
as compared to CO. For CO2 and C3O2, it is easiest to concentrate on the mass of carbon that
combines with 1 g of oxygen. From the formulas (three carbon atoms per two oxygen atoms in
C3O2 versus one carbon atom per two oxygen atoms in CO2), C3O2 will have three times the mass
of carbon that combines per gram of oxygen as compared to CO2. As expected, the mass ratios are
whole numbers as predicted by the law of multiple proportions.
25. Hydrazine: 1.44 × g H/g N; ammonia: 2.16 × g H/g N; hydrogen azide:
2.40 × g H/g N. Let's try all the ratios:
= 6.00; = 9.00; = 1.00; = 1.50 =
All the masses of hydrogen in these three compounds can be expressed as simple whole number
ratios. The g H/g N in hydrazine, ammonia, and hydrogen azide are in the ratios 6:9:1.
26. Compound 1: 21.8 g C and 58.2 g O (80.0 – 21.8 = mass O)
Compound 2: 34.3 g C and 45.7 g O (80.0 – 34.3 = mass O)
The mass of carbon that combines with 1.0 g of oxygen is:
Compound 1: = 0.375 g C/g O
Compound 2: = 0.751 g C/g O
The ratio of the masses of carbon that combine with 1 g of oxygen is ; this supports
the law of multiple proportions because this carbon ratio is a small whole number.
27. a. True; b. False; compounds have constant composition.
c. True; d. True; e. True
,6 CHAPTER 2 ATOMS, MOLECULES, AND IONS
28. If the formula is InO, then one atomic mass of In would combine with one atomic mass of O, or:
, A = atomic mass of In = 76.54
If the formula is In2O3, then two times the atomic mass of In will combine with three times the
atomic mass of O, or:
, A = atomic mass of In = 114.8
The latter number is the atomic mass of In used in the modern periodic table.
29. To get the atomic mass of H to be 1.00, we divide the mass that reacts with 1.00 g of oxygen by
0.126, that is, 0.126/0.126 = 1.00. To get Na, Mg, and O on the same scale, we do the same
division.
Na: = 22.8; Mg: = 11.9; O: = 7.94
H O
Na Mg
Relative value 1.00 7.94 22.8 11.9
Accepted value 1.0079 15.999 22.99 24.31
The atomic masses of O and Mg are incorrect. The atomic masses of H and Na are close.
Something must be wrong about the assumed formulas of the compounds. It turns out that the
correct formulas are H2O, Na2O, and MgO. The smaller discrepancies result from the error in the
assumed atomic mass of H.
The Nature of the Atom
30. Deflection of cathode rays by magnetic and electrical fields led to the conclusion that they were
negatively charged. The cathode ray was produced at the negative electrode and repelled by the
negative pole of the applied electrical field. β particles are electrons. A cathode ray is a stream of
electrons (β particles).
31. The plum pudding model postulated that an atom consisted of a diffuse positive charge with
negative electrons embedded randomly in it. If the plum pudding model was correct, then the alpha
particle used in Rutherford’s metal foil experiment should easily pass through the atom with little
or no deflection. In Rutherford’s experiment, most alpha particles did pass through, but some alpha
particles were deflected at large angles. Because of the severe deflections of some alpha particles,
the plum pudding model could not be correct.
32. Statement d is true. For statement a, neutrons in the nucleus are neutral in charge. For statement
b, the atom consists of a tiny dense nucleus with electrons around the nucleus at relatively large
distances. An atom is mostly empty space. For statement c, the nucleus contains most of the mass
,CHAPTER 2 ATOMS, MOLECULES, AND IONS 7
of the nucleus. For statement e, the number of protons in a neutral atom is equal to the number of
electrons.
33. From section 2.6, the nucleus has “a diameter of about 10−13 cm” and the electrons “move about
the nucleus at an average distance of about 10− 8 cm from it.” We will use these statements to help
determine the densities. Density of hydrogen nucleus (contains one proton only):
Vnucleus =
d = density =
Density of H atom (contains one proton and one electron):
Vatom =
d=
34. 5.93 × 10‒18 C × = 37 negative (electron) charges on the oil drop
35. First, divide all charges by the smallest quantity, 6.40 × 10− 13 .
= 4.00; = 12.00; = 6.00
Because all charges are whole number multiples of 6.40 × 10− 13 zirkombs, the charge on one
electron could be 6.40 × 10− 13 zirkombs. However, 6.40 × 10− 13 zirkombs could be the charge of
two electrons (or three electrons, etc.). All one can conclude is that the charge of an electron is
6.40 × 10− 13 zirkombs or an integer fraction of 6.40 × 10− 13 .
36. The proton and neutron have similar mass, with the mass of the neutron slightly larger than that
of the proton. Each of these particles has a mass approximately 1800 times greater than that of an
electron. The combination of the protons and neutrons in the nucleus makes up the bulk of the
mass of an atom, but the electrons make the greatest contribution to the chemical properties of the
atom.
37. J. J. Thomson discovered electrons. He postulated that all atoms must contain electrons, but
Thomson also postulated that atoms must contain positive charge for the atom to be electrically
neutral. Henri Becquerel discovered radioactivity. Lord Rutherford proposed the nuclear model of
the atom. Dalton's original model proposed that atoms were indivisible particles (i.e., atoms had
no internal structure). Thomson and Becquerel discovered subatomic particles, and Rutherford's
model attempted to describe the internal structure of the atom composed of these subatomic
particles. In addition, the existence of isotopes, atoms of the same element but with a different
mass, had to be included in the model.
, 8 CHAPTER 2 ATOMS, MOLECULES, AND IONS
Elements, Ions, and the Periodic Table
38. a. A molecule has no overall charge (an equal number of electrons and protons are present).
Ions, on the other hand, have electrons added to form anions (negatively charged ions) or
electrons removed to form cations (positively charged ions).
b. The sharing of electrons between atoms is a covalent bond. An ionic bond is the force of
attraction between two oppositely charged ions.
c. A molecule is a collection of atoms held together by covalent bonds. A compound is
composed of two or more different elements having constant composition. Covalent and/or
ionic bonds can hold the atoms together in a compound. Another difference is that molecules
do not necessarily have to be compounds. H2 is two hydrogen atoms held together by a
covalent bond. H2 is a molecule, but it is not a compound; H2 is a diatomic element.
d. An anion is a negatively charged ion; for example, Cl−, O2− , and SO42− are all anions. A
cation is a positively charged ion; for example, Na+, Fe3+, and NH4+ are all cations.
39. The atomic number of an element is equal to the number of protons in the nucleus of an atom of
that element. The mass number is the sum of the number of protons plus neutrons in the nucleus.
The atomic mass is the actual mass of a particular isotope (including electrons). As is discussed in
Chapter 3, the average mass of an atom is taken from a measurement made on a large number of
atoms. The average atomic mass value is listed in the periodic table.
40. a. Metals: Mg, Ti, Au, Bi, Ge, Eu, and Am. Nonmetals: Si, B, At, Rn, and Br.
b. Si, Ge, B, and At. The elements at the boundary between the metals and the nonmetals are B,
Si, Ge, As, Sb, Te, Po, and At. Aluminum has mostly properties of metals, so it is generally
not classified as a metalloid.
41. a. The noble gases are He, Ne, Ar, Kr, Xe, Rn, and Og (helium, neon, argon, krypton, xenon,
radon, and oganesson). Radon and oganesson have only radioactive isotopes. In the periodic
table, the whole number enclosed in parentheses is the mass number of the longest-lived
isotope of the element.
b. Promethium (Pm) and technetium (Tc)
42. Carbon is a nonmetal. Silicon and germanium are called metalloids as they exhibit both metallic
and nonmetallic properties. Tin and lead are metals. Thus metallic character increases as one goes
down a family in the periodic table. The metallic character decreases from left to right across the
periodic table.
43. Use the periodic table to identify the elements.
a. Cl; halogen b. Be; alkaline earth metal
c. Eu; lanthanide metal d. Hf; transition metal
Chemical Principles 9th Edition Zumdahl
Important Notes
The file includes the complete test bank, organized chapter by chapter.
A sample of selected pages has been provided for preview.
All available appendices and Excel files (if included in the original resources) are
provided.
We continuously update our files to ensure you receive the latest and most accurate
editions.
New editions are added regularly – stay connected for updates!
Purchase Guarantee
If you believe you have purchased the wrong file, don’t worry. Contact us anytime and we
will gladly replace it with the correct version.
Contact Email:
,CHAPTER 2
ATOMS, MOLECULES, AND IONS
Discussion Questions
1. When water boils, H2O(l) is converted to H2O(g). So, water vapor is present in the bubbles
(answer d). For H2(g) and O2(g) to form, a lot more energy must be added to break down water
into its elements.
2. A singular atom of any element is neither a solid nor a liquid nor a gas (statement e is correct).
Only collections of atoms can be characterized as a solid, liquid, or gas.
3. The data needed would be the mass of chalk before writing your name and the mass of chalk
after writing your name. In a separate experiment, weigh a sample of chalk that has a known
number of “chalk molecules,” then determine the mass of one “chalk molecule.” Once the mass
of a “chalk molecule” is known, one can convert the mass of chalk used to write your name into
the number of “chalk molecules.” Note that chalk is composed of the ionic compound calcium
carbonate, CaCO3. Calcium carbonate is an ionic compound composed of ions, not molecules.
This is why “chalk molecules” is put in quotation marks.
4. a. Thomson’s plum pudding model of the atom consisted of a diffuse cloud of positive charge
with the negative charged electrons embedded randomly in it. Since electrons were the
centerpiece of his model, Thomson would probably consider electrons as the most important
particle. When different atoms come together to react to form a compound, it is the electrons
that are shared or transferred to form new substances.
b. The protons are next most important. The number of protons dictates how many electrons are
required to form specific neutral atoms or charged ions, which is related to the compounds
that form.
c. Thomson applied high voltage between metal electrodes in evacuated tubes to produce a
stream of negative charged particles. Any model that explains the results of the cathode ray
experiments would be a possible answer to this question.
5. An ice cube has the H2O molecules packed very closely together. Steam consists of separate H2O
molecules with lots of space between them. Any drawing illustrating these differences between
the two states is fine. Also illustrated should be that the number and size of the H2O molecules
do not change when an ice cube is converted to steam in a closed container. Because the number
of water molecules doesn’t change, the mass will not change.
6. Assuming no substances can enter or leave the glass container, then the mass before the reaction
should be identical to the mass after the reaction. In a chemical reaction, some bonds are broken
between the atoms in the reactant compounds and some new bonds form in the product
compounds. But the number and types of atoms are the same before a reaction as compared to
after a reaction. Since atoms are conserved in a chemical reaction, mass is conserved. Answer b
is correct.
,2 CHAPTER 2 ATOMS, MOLECULES, AND IONS
7. Natural niacin and commercially produced niacin have the exact same formula of C6H5NO2.
Therefore, both sources produce niacin having an identical nutritional value. There may be other
compounds present in natural niacin that would increase the nutritional value, but the nutritional
value due to just niacin is identical to the commercially produced niacin.
8. Yes, many questions are raised from Dalton’s theory. For example, how atoms are different from
one another; how atoms are of the same element identical to each other; how atoms are held
together when in compounds; if atoms are particles, what their mass is; etc.
9. Mass is conserved in a chemical reaction because atoms are conserved. Chemical reactions
involve the reorganization of atoms, so formulas change in a chemical reaction, but the number
and types of atoms do not change. Because the atoms do not change in a chemical reaction, mass
must not change. In this equation we have two oxygen atoms and four hydrogen atoms both
before and after the reaction occurs.
10. a. Atoms have specific masses and are neither created nor destroyed by chemical reactions.
Because atoms are conserved in a chemical reaction, mass cannot change in a chemical
reaction. Mass is conserved.
b. The composition of a substance depends on the number and kinds of atoms that form it. A
certain compound always has the same number and kinds of atoms in its formula.
c. Compounds of the same elements differ only in the numbers of atoms of the elements forming
them, that is, NO, N2O, NO2.
11. Some elements exist as molecular substances. That is, hydrogen normally exists as H2 molecules,
not single hydrogen atoms. The same is true for N2, O2, F2, Cl2, etc.
12. The number of protons identifies the element and determines how many electrons are required to
balance the total positive charge from the protons. So, identity and number of electrons in the
neutral element can be determined. However, the number of neutrons cannot be determined from
just the number of protons.
13. The various elements are composed of different isotopes. For example, carbon is made up of a
mixture of 12C, 13C, and 14C isotopes, with each isotope having a different mass. The mass of
carbon listed in the periodic table is an average mass of a mixture of the various carbon isotopes.
None of the isotopes have a mass of 12.011, but a large sample of carbon behaves as if each
carbon has an average mass of 12.011. Answer a is correct.
14. The electrons are on the outside of the nucleus; these are the particles that are easiest to access.
Ions form when electrons are added or removed from an atom. Immense energy is required to
add or subtract protons or neutrons to or from a nucleus.
15. Answer b is correct; H2O consists of 2 H atoms bound to one O atom. Because a hydrogen
atom’s mass is not equivalent to the mass of an oxygen atom, answer a is false. The other
answers assume an incorrect formula for H2O.
,CHAPTER 2 ATOMS, MOLECULES, AND IONS 3
16. Barium is an alkaline earth metal. All alkaline earth metals form 2+ charge cations when in ionic
compounds. The charge for most transition metal ions is not easily deduced from its position in
the periodic table. For most transition metal compounds, the charge of the metal ion is included
in the name.
17. Calcium dichloride follows the covalent rules of nomenclature, that is, the use of di-, tri-, tetra-,
etc., to indicate number of atoms in a formula. When the metal calcium is in a compound, it
forms an ionic compound. So, we use the ionic rules, and calcium chloride is the correct name.
For ionic compounds, the charges of each ion can be predicted (generally) from the periodic
table; if the charges of the ions are known, then the formula can be deduced.
18. For each experiment, divide the larger number by the smaller. In doing so, we get:
experiment 1 X = 1.0 Y = 10.5
experiment 2 Y = 1.4 Z = 1.0
experiment 3 X = 1.0 Y = 3.5
Our assumption about formulas dictates the rest of the solution. For example, if we assume that
the formula of the compound in experiment 1 is XY and that of experiment 2 is YZ, we get
relative masses of:
X = 2.0; Y = 21; Z = 15 (= 21/1.4)
and a formula of X3Y for experiment 3 [three times as much X must be present in experiment 3
as compared to experiment 1 (10.5/3.5 = 3)].
However, if we assume the formula for experiment 2 is YZ and that of experiment 3 is XY, then
we get:
X = 2.0; Y = 7.0; Z = 5.0 (= 7.0/1.4)
and a formula of XY3 for experiment 1.
Any answer that is consistent with your initial assumptions is correct.
The answer to part d depends on which (if any) of experiments 1 and 3 have a formula of XY in
the compound. If the compound in experiment 1 has formula XY, then:
21 g XY × = 19.2 g Y (and 1.8 g X)
If the compound in experiment 3 has the XY formula, then:
21 g XY × = 16.3 g Y (and 4.7 g X)
Note that it could be that neither experiment 1 nor experiment 3 has XY as the formula.
Therefore, there is no way of knowing an absolute answer here.
,4 CHAPTER 2 ATOMS, MOLECULES, AND IONS
19. a. The smaller parts are electrons and the nucleus. The nucleus is broken down into protons and
neutrons, which can be broken down into quarks. For our purpose, electrons, neutrons, and
protons are the key smaller parts of an atom.
b. All atoms of hydrogen have 1 proton in the nucleus. Different isotopes of hydrogen have 0, 1,
or 2 neutrons in the nucleus. Because we are talking about atoms, this implies a neutral
charge, which dictates 1 electron present for all hydrogen atoms. If charged ions were
included, then different ions/atoms of H could have different numbers of electrons.
c. Hydrogen atoms always have 1 proton in the nucleus, and helium atoms always have 2
protons in the nucleus. The number of neutrons can be the same for a hydrogen atom and a
helium atom. Tritium (3H) and 4He both have 2 neutrons. Assuming neutral atoms, then the
number of electrons will be 1 for hydrogen and 2 for helium.
d. Water (H2O) is always 1 g hydrogen for every 8 g of O present, whereas H2O2 is always 1 g
hydrogen for every 16 g of O present. These are distinctly different compounds, each with its
own unique relative number and types of atoms present.
e. A chemical equation involves a reorganization of the atoms. Bonds are broken between atoms
in the reactants, and new bonds are formed in the products. However, the number and types of
atoms between reactants and products do not change. Because atoms are conserved in a
chemical reaction, mass is also conserved.
Development of the Atomic Theory
20. Law of conservation of mass: Mass is neither created nor destroyed. The total mass before a
chemical reaction always equals the total mass after a chemical reaction.
Law of definite proportion: A given compound always contains exactly the same proportion of
elements by mass. For example, water is always 1 g hydrogen for every 8 g oxygen.
Law of multiple proportions: When two elements form a series of compounds, the ratios of the
mass of the second element that combines with 1 g of the first element can always be reduced to
small whole numbers. For CO2 and CO discussed in section 2.2, the mass ratios of oxygen that
react with 1 g carbon in each compound are in a 2:1 ratio.
21. From Avogadro’s hypothesis (law), volume ratios are equal to molecule ratios at constant
temperature and pressure. Therefore, we can write a balanced equation using the volume data, Cl2
+ 5 F2 → 2 X. Two molecules of X contain 10 atoms of F and two atoms of Cl. The formula
of X is ClF5 for a balanced equation.
22. a. The composition of a substance depends on the numbers of atoms of each element making up
the compound (depends on the formula of the compound) and not on the composition of the
mixture from which it was formed.
b. Avogadro’s hypothesis (law) implies that volume ratios are proportional to molecule ratios at
constant temperature and pressure: H2 + Cl2 → 2 H Cl. From the balanced equation, the
volume of H Cl produced will be twice the volume of H 2 (or Cl2) reacted.
,CHAPTER 2 ATOMS, MOLECULES, AND IONS 5
23. Avogadro’s hypothesis (law) implies that volume ratios are equal to molecule ratios at constant
temperature and pressure. Here, 1 volume of N2 reacts with 3 volumes of H2 to produce 2 volumes
of the gaseous product or, in terms of molecule ratios,
1 N2 + 3 H2 → 2 product
For the equation to be balanced, the product must be NH3.
24. For CO and CO2, it is easiest to concentrate on the mass of oxygen that combines with 1 g of
carbon. From the formulas (two oxygen atoms per carbon atom in CO2 versus one oxygen atom
per carbon atom in CO), CO2 will have twice the mass of oxygen that combines per gram of carbon
as compared to CO. For CO2 and C3O2, it is easiest to concentrate on the mass of carbon that
combines with 1 g of oxygen. From the formulas (three carbon atoms per two oxygen atoms in
C3O2 versus one carbon atom per two oxygen atoms in CO2), C3O2 will have three times the mass
of carbon that combines per gram of oxygen as compared to CO2. As expected, the mass ratios are
whole numbers as predicted by the law of multiple proportions.
25. Hydrazine: 1.44 × g H/g N; ammonia: 2.16 × g H/g N; hydrogen azide:
2.40 × g H/g N. Let's try all the ratios:
= 6.00; = 9.00; = 1.00; = 1.50 =
All the masses of hydrogen in these three compounds can be expressed as simple whole number
ratios. The g H/g N in hydrazine, ammonia, and hydrogen azide are in the ratios 6:9:1.
26. Compound 1: 21.8 g C and 58.2 g O (80.0 – 21.8 = mass O)
Compound 2: 34.3 g C and 45.7 g O (80.0 – 34.3 = mass O)
The mass of carbon that combines with 1.0 g of oxygen is:
Compound 1: = 0.375 g C/g O
Compound 2: = 0.751 g C/g O
The ratio of the masses of carbon that combine with 1 g of oxygen is ; this supports
the law of multiple proportions because this carbon ratio is a small whole number.
27. a. True; b. False; compounds have constant composition.
c. True; d. True; e. True
,6 CHAPTER 2 ATOMS, MOLECULES, AND IONS
28. If the formula is InO, then one atomic mass of In would combine with one atomic mass of O, or:
, A = atomic mass of In = 76.54
If the formula is In2O3, then two times the atomic mass of In will combine with three times the
atomic mass of O, or:
, A = atomic mass of In = 114.8
The latter number is the atomic mass of In used in the modern periodic table.
29. To get the atomic mass of H to be 1.00, we divide the mass that reacts with 1.00 g of oxygen by
0.126, that is, 0.126/0.126 = 1.00. To get Na, Mg, and O on the same scale, we do the same
division.
Na: = 22.8; Mg: = 11.9; O: = 7.94
H O
Na Mg
Relative value 1.00 7.94 22.8 11.9
Accepted value 1.0079 15.999 22.99 24.31
The atomic masses of O and Mg are incorrect. The atomic masses of H and Na are close.
Something must be wrong about the assumed formulas of the compounds. It turns out that the
correct formulas are H2O, Na2O, and MgO. The smaller discrepancies result from the error in the
assumed atomic mass of H.
The Nature of the Atom
30. Deflection of cathode rays by magnetic and electrical fields led to the conclusion that they were
negatively charged. The cathode ray was produced at the negative electrode and repelled by the
negative pole of the applied electrical field. β particles are electrons. A cathode ray is a stream of
electrons (β particles).
31. The plum pudding model postulated that an atom consisted of a diffuse positive charge with
negative electrons embedded randomly in it. If the plum pudding model was correct, then the alpha
particle used in Rutherford’s metal foil experiment should easily pass through the atom with little
or no deflection. In Rutherford’s experiment, most alpha particles did pass through, but some alpha
particles were deflected at large angles. Because of the severe deflections of some alpha particles,
the plum pudding model could not be correct.
32. Statement d is true. For statement a, neutrons in the nucleus are neutral in charge. For statement
b, the atom consists of a tiny dense nucleus with electrons around the nucleus at relatively large
distances. An atom is mostly empty space. For statement c, the nucleus contains most of the mass
,CHAPTER 2 ATOMS, MOLECULES, AND IONS 7
of the nucleus. For statement e, the number of protons in a neutral atom is equal to the number of
electrons.
33. From section 2.6, the nucleus has “a diameter of about 10−13 cm” and the electrons “move about
the nucleus at an average distance of about 10− 8 cm from it.” We will use these statements to help
determine the densities. Density of hydrogen nucleus (contains one proton only):
Vnucleus =
d = density =
Density of H atom (contains one proton and one electron):
Vatom =
d=
34. 5.93 × 10‒18 C × = 37 negative (electron) charges on the oil drop
35. First, divide all charges by the smallest quantity, 6.40 × 10− 13 .
= 4.00; = 12.00; = 6.00
Because all charges are whole number multiples of 6.40 × 10− 13 zirkombs, the charge on one
electron could be 6.40 × 10− 13 zirkombs. However, 6.40 × 10− 13 zirkombs could be the charge of
two electrons (or three electrons, etc.). All one can conclude is that the charge of an electron is
6.40 × 10− 13 zirkombs or an integer fraction of 6.40 × 10− 13 .
36. The proton and neutron have similar mass, with the mass of the neutron slightly larger than that
of the proton. Each of these particles has a mass approximately 1800 times greater than that of an
electron. The combination of the protons and neutrons in the nucleus makes up the bulk of the
mass of an atom, but the electrons make the greatest contribution to the chemical properties of the
atom.
37. J. J. Thomson discovered electrons. He postulated that all atoms must contain electrons, but
Thomson also postulated that atoms must contain positive charge for the atom to be electrically
neutral. Henri Becquerel discovered radioactivity. Lord Rutherford proposed the nuclear model of
the atom. Dalton's original model proposed that atoms were indivisible particles (i.e., atoms had
no internal structure). Thomson and Becquerel discovered subatomic particles, and Rutherford's
model attempted to describe the internal structure of the atom composed of these subatomic
particles. In addition, the existence of isotopes, atoms of the same element but with a different
mass, had to be included in the model.
, 8 CHAPTER 2 ATOMS, MOLECULES, AND IONS
Elements, Ions, and the Periodic Table
38. a. A molecule has no overall charge (an equal number of electrons and protons are present).
Ions, on the other hand, have electrons added to form anions (negatively charged ions) or
electrons removed to form cations (positively charged ions).
b. The sharing of electrons between atoms is a covalent bond. An ionic bond is the force of
attraction between two oppositely charged ions.
c. A molecule is a collection of atoms held together by covalent bonds. A compound is
composed of two or more different elements having constant composition. Covalent and/or
ionic bonds can hold the atoms together in a compound. Another difference is that molecules
do not necessarily have to be compounds. H2 is two hydrogen atoms held together by a
covalent bond. H2 is a molecule, but it is not a compound; H2 is a diatomic element.
d. An anion is a negatively charged ion; for example, Cl−, O2− , and SO42− are all anions. A
cation is a positively charged ion; for example, Na+, Fe3+, and NH4+ are all cations.
39. The atomic number of an element is equal to the number of protons in the nucleus of an atom of
that element. The mass number is the sum of the number of protons plus neutrons in the nucleus.
The atomic mass is the actual mass of a particular isotope (including electrons). As is discussed in
Chapter 3, the average mass of an atom is taken from a measurement made on a large number of
atoms. The average atomic mass value is listed in the periodic table.
40. a. Metals: Mg, Ti, Au, Bi, Ge, Eu, and Am. Nonmetals: Si, B, At, Rn, and Br.
b. Si, Ge, B, and At. The elements at the boundary between the metals and the nonmetals are B,
Si, Ge, As, Sb, Te, Po, and At. Aluminum has mostly properties of metals, so it is generally
not classified as a metalloid.
41. a. The noble gases are He, Ne, Ar, Kr, Xe, Rn, and Og (helium, neon, argon, krypton, xenon,
radon, and oganesson). Radon and oganesson have only radioactive isotopes. In the periodic
table, the whole number enclosed in parentheses is the mass number of the longest-lived
isotope of the element.
b. Promethium (Pm) and technetium (Tc)
42. Carbon is a nonmetal. Silicon and germanium are called metalloids as they exhibit both metallic
and nonmetallic properties. Tin and lead are metals. Thus metallic character increases as one goes
down a family in the periodic table. The metallic character decreases from left to right across the
periodic table.
43. Use the periodic table to identify the elements.
a. Cl; halogen b. Be; alkaline earth metal
c. Eu; lanthanide metal d. Hf; transition metal
