www.pdflobby.com CHEMISTRY Raymond Chang Williams College Kenneth A. Goldsby Florida State University www.pdflobby.
www.pdflobby.com CHEMISTRY Raymond Chang Williams College Kenneth A. Goldsby Florida State University www.pdflobby.
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C h e m i s t r y 1 2 t h E d i t i o n C h a n g S o l u t i o n s M F u l l Dh ot tw p n : l / o / at de :s t b a n k l i v e . c o m / d o w n l o a d / c h e
CHAPTER 2 ATOMS, MOLECULES, AND IONS Problem Categories Biological: 2.79, 2.80. Conceptual: 2.31, 2.32, 2.33, 2.34, 2.61, 2.65, 2.71, 2.72, 2.81, 2.82, 2.93, 2.103, 2.113. Descriptive: 2.24, 2.25, 2.26, 2.49, 2.50, 2.66, 2.70, 2.76, 2.84, 2.85, 2.86, 2.87, 2.88, 2.90, 2.91, 2.92, 2.94, 2.98, 2.101, 2.114. Environmental: 2.122. Organic: 2.47, 2.48, 2.69, 2.105, 2.107, 2.108, 2.115. Difficulty Level Easy: 2.7, 2.8, 2.13, 2.14, 2.15, 2.16, 2.23, 2.31, 2.32, 2.33, 2.43, 2.44, 2.45, 2.46, 2.47, 2.48, 2.62, 2.91, 2.92, 2.99, 2.100. Medium: 2.17, 2.18, 2.24. 2.26, 2.34, 2.35, 2.36, 2.49, 2.50, 2.57, 2.58, 2.59, 2.60, 2.61, 2.63, 2.64, 2.65, 2.66, 2.67, 2.68, 2.69, 2.70, 2.71, 2.72, 2.73, 2.74, 2.75, 2.76, 2.79, 2.80, 2.81, 2.82, 2.83, 2.84, 2.85, 2.86, 2.88, 2.89, 2.90, 2.93, 2.94, 2.95, 2.96, 2.98, 2.101, 2.102, 2.103, 2.110, 2.112, 2.114, 2.115. Difficult: 2.25, 2.77, 2.78, 2.87, 2.97, 2.104, 2.105, 2.106, 2.107, 2.108, 2.109, 2.111, 2.113. 2.7
First, convert 1 cm to picometers. 1 cm
0.01 m 1 pm 1 1010 pm 12 1 cm 1 10 m
? He atoms (1 1010 pm)
Note that you are given information to set up the unit factor relating meters and miles. ratom 104 rnucleus 104 2.0 cm
1 108 He atoms
1m 1 mi 0.12 mi 100 cm 1609 m
For iron, the atomic number Z is 26. Therefore the mass number A is: A 26 28 54
Strategy: The 239 in Pu-239 is the mass number. The mass number (A) is the total number of neutrons and protons present in the nucleus of an atom of an element. You can look up the atomic number (number of protons) on the periodic table. Solution: mass number number of protons number of neutrons number of neutrons mass number number of protons 239 94 145
Isotope No. Protons No. Neutrons
d o w n l o a d
c h a p t e r s
i n s t a n t l y
CHAPTER 2: ATOMS, MOLECULES, AND IONS
Isotope No. Protons No. Neutrons No. Electrons 23 11 Na
The accepted way to denote the atomic number and mass number of an element X is as follows:
where, A mass number Z atomic number (a)
Helium and selenium are nonmetals whose name ends with ium. (Tellerium is a metalloid whose name ends in ium.)
Metallic character increases as you progress down a group of the periodic table. For example, moving down Group 4A, the nonmetal carbon is at the top and the metal lead is at the bottom of the group.
Metallic character decreases from the left side of the table (where the metals are located) to the right side of the table (where the nonmetals are located).
The following data were measured at 20C. 3
F and Cl are Group 7A elements; they should have similar chemical properties. Na and K are both Group 1A elements; they should have similar chemical properties. P and N are both Group 5A elements; they should have similar chemical properties.
This is a polyatomic molecule that is an elemental form of the substance. It is not a compound. This is a polyatomic molecule that is a compound. This is a diatomic molecule that is a compound.
This is a diatomic molecule that is a compound. This is a polyatomic molecule that is a compound. This is a polyatomic molecule that is the elemental form of the substance. It is not a compound.
There are more than two correct answers for each part of the problem. (a) (d)
N2, S8, H2 NH3, NO, CO, CO2, SO2
H2 and F2 (b) H2O and C12H22O11 (sucrose)
CHAPTER 2: ATOMS, MOLECULES, AND IONS
Ion No. protons No. electrons
The atomic number (Z) is the number of protons in the nucleus of each atom of an element. You can find this on a periodic table. The number of electrons in an ion is equal to the number of protons minus the charge on the ion. number of electrons (ion) number of protons charge on the ion
Ion No. protons No. electrons
Sodium ion has a 1 charge and oxide has a 2 charge. The correct formula is Na2O. The iron ion has a 2 charge and sulfide has a 2 charge. The correct formula is FeS. The correct formula is Co2(SO4)3 Barium ion has a 2 charge and fluoride has a 1 charge. The correct formula is BaF2.
The copper ion has a 1 charge and bromide has a 1 charge. The correct formula is CuBr. The manganese ion has a 3 charge and oxide has a 2 charge. The correct formula is Mn2O3. 2 We have the Hg2 ion and iodide (I ). The correct formula is Hg2I2. Magnesium ion has a 2 charge and phosphate has a 3 charge. The correct formula is Mg3(PO4)2.
Strategy: An empirical formula tells us which elements are present and the simplest whole-number ratio of their atoms. Can you divide the subscripts in the formula by some factor to end up with smaller wholenumber subscripts?
Solution: (a) (b) (c) (d)
Dividing both subscripts by 2, the simplest whole number ratio of the atoms in Al2Br6 is AlBr3. Dividing all subscripts by 2, the simplest whole number ratio of the atoms in Na2S2O4 is NaSO2. The molecular formula as written, N2O5, contains the simplest whole number ratio of the atoms present. In this case, the molecular formula and the empirical formula are the same. The molecular formula as written, K2Cr2O7, contains the simplest whole number ratio of the atoms present. In this case, the molecular formula and the empirical formula are the same.
The molecular formula of glycine is C2H5NO2.
The molecular formula of ethanol is C2H6O.
Compounds of metals with nonmetals are usually ionic. Nonmetal-nonmetal compounds are usually molecular. Ionic: Molecular:
LiF, BaCl2, KCl SiCl4, B2H6, C2H4
Compounds of metals with nonmetals are usually ionic. Nonmetal-nonmetal compounds are usually molecular. Ionic: Molecular:
NaBr, BaF2, CsCl. CH4, CCl4, ICl, NF3
CHAPTER 2: ATOMS, MOLECULES, AND IONS
sodium chromate potassium hydrogen phosphate hydrogen bromide (molecular compound) hydrobromic acid lithium carbonate potassium dichromate ammonium nitrite
phosphorus trifluoride phosphorus pentafluoride tetraphosphorus hexoxide cadmium iodide strontium sulfate aluminum hydroxide sodium carbonate decahydrate
Strategy: When naming ionic compounds, our reference for the names of cations and anions is Table 2.3 of the text. Keep in mind that if a metal can form cations of different charges, we need to use the Stock system. In the Stock system, Roman numerals are used to specify the charge of the cation. The metals that have only 2 2 one charge in ionic compounds are the alkali metals (1), the alkaline earth metals (2), Ag , Zn , Cd , and 3 Al . When naming acids, binary acids are named differently than oxoacids. For binary acids, the name is based on the nonmetal. For oxoacids, the name is based on the polyatomic anion. For more detail, see Section 2.7 of the text. Solution:
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 .
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 chloride ion has a 1 charge, the Fe ion has a 2 charge. The correct name is iron(II) chloride.
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.
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.
(m) This is an ionic compound in which the metal cation (Na ) has only one charge. The O2 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. (n)
iron(III) chloride hexahydrate
Strategy: When writing formulas of molecular compounds, the prefixes specify the number of each type of atom in the compound.
When writing formulas of ionic compounds, the subscript of the cation is numerically equal to the charge of the anion, and the subscript of the anion is numerically equal to the charge on the cation. If the charges of the cation and anion are numerically equal, then no subscripts are necessary. Charges of common cations and
CHAPTER 2: ATOMS, MOLECULES, AND IONS
anions are listed in Table 2.3 of the text. Keep in mind that Roman numerals specify the charge of the cation, not the number of metal atoms. Remember that a Roman numeral is not needed for some metal cations, because the charge is known. These metals are the alkali metals (1), the alkaline earth metals (2), Ag , 2 2 3 Zn , Cd , and Al . When writing formulas of oxoacids, you must know the names and formulas of polyatomic anions (see Table 2.3 of the text). Solution: (a)
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. 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. 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. Hydroiodic tells you that the anion of this binary acid is iodide, I . The correct formula is HI(aq). Na is an alkali metal. It only forms a 1 cation. The polyatomic ion ammonium, NH4 , has a 1 charge 3 and the polyatomic ion phosphate, PO4 , has a 3 charge. To balance the charge, you need 2 Na cations. The correct formula is Na2(NH4)PO4. The Roman numeral II tells you that the Pb cation has a 2 charge. The polyatomic ion carbonate, 2 CO3 , has a 2 charge. Since, the charges are numerically equal, no subscripts are necessary in the formula. The correct formula is PbCO3. 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. 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. 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. The Roman numeral I tells you that the Hg cation has a 1 charge. However, this cation exists as 2 2 Hg2 . Iodide has a 1 charge. You need two iodide ion to balance the 2 charge of Hg2 . The correct formula is Hg2I2. 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.
Let’s compare the ratio of the fluorine masses in the two compounds. 3.55 g F 1.50 2.37 g F
This calculation indicates that there is 1.5 times more fluorine by mass in SF6 compared to the other compound. The value of n is: 6 n 4 1.5 This is consistent with the Law of Multiple Proportions which states that if two elements combine to form more than one compound, the masses of one element that combine with a fixed mass of the other element are in ratios of small whole numbers. In this case, the ratio of the masses of fluorine in the two compounds is 6:4 or 3:2.
CHAPTER 2: ATOMS, MOLECULES, AND IONS
dinitrogen pentoxide (N2O5) boron trifluoride (BF3) dialuminum hexabromide (Al2Br6)
Uranium is radioactive. It loses mass because it constantly emits alpha () particles.
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.
The number of protons 65 35 30. The element that contains 30 protons is zinc, Zn. There are two 2 fewer electrons than protons, so the charge of the cation is 2. The symbol for this cation is Zn .
Atomic number 127 74 53. This anion has 53 protons, so it is an iodide ion. Since there is one more electron than protons, the ion has a 1 charge. The correct symbol is I .
NaCl is an ionic compound; it doesn’t form molecules.
Yes. The law of multiple proportions requires that the masses of sulfur combining with phosphorus must be in the ratios of small whole numbers. For the three compounds shown, four phosphorus atoms combine with three, seven, and ten sulfur atoms, respectively. If the atom ratios are in small whole number ratios, then the mass ratios must also be in small whole number ratios.
The species and their identification are as follows:
(10 electrons), Ar and P (b)
molecular, C3H8 empirical, C3H8
(18 electrons), Fe
and V (23 electrons), Sn 127 53 I
molecular, C2H2 empirical, CH
molecular, C2H6 empirical, CH3
Species with the same number of protons and electrons will be neutral. A, F, G. Species with more electrons than protons will have a negative charge. B, E. Species with more protons than electrons will have a positive charge. C, D.
Ne, 10 p, 10 n W, 74 p, 108 n
BaO, barium oxide Al2S3, aluminum sulfide
Cu, 29 p, 34 n Po, 84 p, 119 n (b) (d)
O3 CH4 KBr S P4 LiF
SO2 S8 Cs N2O5 O O2
and Ag (46 electrons).
(a) (b) (c) (d) (e) (f) 2.73
molecule and compound element and molecule element molecule and compound element element and molecule
element and molecule molecule and compound compound element element and molecule compound
Ag, 47 p, 60 n Pu, 94 p, 140 n
Ca3P2, calcium phosphide Li3N, lithium nitride
molecular, C6H6 empirical, CH
CHAPTER 2: ATOMS, MOLECULES, AND IONS
When an anion is formed from an atom, you have the same number of protons attracting more electrons. The electrostatic attraction is weaker, which allows the electrons on average to move farther from the nucleus. An anion is larger than the atom from which it is derived. When a cation is formed from an atom, you have the same number of protons attracting fewer electrons. The electrostatic attraction is stronger, meaning that on average, the electrons are pulled closer to the nucleus. A cation is smaller than the atom from which it is derived.
Rutherford’s experiment is described in detail in Section 2.2 of the text. From the average magnitude of scattering, Rutherford estimated the number of protons (based on electrostatic interactions) in the nucleus.
Assuming that the nucleus is spherical, the volume of the nucleus is:
4 3 4 r (3.04 1013 cm)3 1.177 1037 cm3 3 3
The density of the nucleus can now be calculated. d
3.82 1023 g m 3.25 1014 g/cm 3 37 3 V 1.177 10 cm
To calculate the density of the space occupied by the electrons, we need both the mass of 11 electrons, and the volume occupied by these electrons. The mass of 11 electrons is:
9.1095 1028 g 1.00205 1026 g 1 electron
The volume occupied by the electrons will be the difference between the volume of the atom and the volume of the nucleus. The volume of the nucleus was calculated above. The volume of the atom is calculated as follows: 186 pm
1 1012 m 1 cm 1.86 108 cm 2 1 pm 1 10 m
4 3 4 r (1.86 108 cm)3 2.695 1023 cm3 3 3
Velectrons Vatom Vnucleus (2.695 10
As you can see, the volume occupied by the nucleus is insignificant compared to the space occupied by the electrons. The density of the space occupied by the electrons can now be calculated. d
1.00205 1026 g m 3.72 104 g/cm 3 V 2.695 1023 cm3
The above results do support Rutherford's model. Comparing the space occupied by the electrons to the volume of the nucleus, it is clear that most of the atom is empty space. Rutherford also proposed that the nucleus was a dense central core with most of the mass of the atom concentrated in it. Comparing
CHAPTER 2: ATOMS, MOLECULES, AND IONS
the density of the nucleus with the density of the space occupied by the electrons also supports Rutherford's model. 2.79
The molecular formula of caffeine is C8H10N4O2. The empirical formula is C4H5N2O.
The empirical and molecular formulas of acetaminophen are C8H9NO2.
Iodate ion is IO32 . The correct formula is Mg(IO3)2.
The formula shown is phosphorous acid. The correct formula for phosphoric acid is H3PO4. Sulfite ion is SO32 . The correct formula is BaSO3.
NH 4 is the ammonium ion. The correct formula is NH4HCO3.
The charge on the tin cation needs to be specified. The correct name is tin(IV) chloride. The charge on the copper ion is +1. The correct name is copper(I) oxide. The charge on the cobalt cation needs to be specified. The correct name is cobalt(II) nitrate. Cr2 O 72 is the dichromate ion. The correct name is sodium dichromate.
Symbol Protons Neutrons Electrons Net Charge
Ionic compounds are typically formed between metallic and nonmetallic elements. In general the transition metals, the actinides, and the lanthanides have variable charges.
Li , alkali metals always have a 1 charge in ionic compounds 2 S I , halogens have a 1 charge in ionic compounds 3 N 3 Al , aluminum always has a 3 charge in ionic compounds Cs , alkali metals always have a 1 charge in ionic compounds 2 Mg , alkaline earth metals always have a 2 charge in ionic compounds.
The symbol Na provides more information than 11Na. The mass number plus the chemical symbol identifies a specific isotope of Na (sodium) while combining the atomic number with the chemical symbol tells you nothing new. Can other isotopes of sodium have different atomic numbers?
The binary Group 7A element acids are: HF, hydrofluoric acid; HCl, hydrochloric acid; HBr, hydrobromic acid; HI, hydroiodic acid. Oxoacids containing Group 7A elements (using the specific examples for chlorine) are: HClO4, perchloric acid; HClO3, chloric acid; HClO2, chlorous acid: HClO, hypochlorous acid.
Examples of oxoacids containing other Group A-block elements are: H3BO3, boric acid (Group 3A); H2CO3, carbonic acid (Group 4A); HNO3, nitric acid and H3PO4, phosphoric acid (Group 5A); and H2SO4, sulfuric acid (Group 6A). Hydrosulfuric acid, H2S, is an example of a binary Group 6A acid while HCN, hydrocyanic acid, contains both a Group 4A and 5A element.
CHAPTER 2: ATOMS, MOLECULES, AND IONS
Mercury (Hg) and bromine (Br2)
Isotope No. Protons No. Neutrons
