60 CHAPTER 2 Atoms, Molecules, and Ions Figure 2.16 Steps for naming molecular and ionic compounds.. SECTION 2.7 Ions and Ionic Compounds 61 Deduce the formulas of the following ionic
Trang 158 CHAPTER 2 Atoms, Molecules, and Ions
Figure 2.15 An electron is
transferred from the sodium atom to the
chlorine atom, giving a sodium ion and
a chloride ion The oppositely charged
ions are attracted to each other and
form a solid lattice
Sodium atom (Na)
Chlorine a t om (C I )
Loses an electron
Gain s a n electron
Electron transfer
Sodium ion (Na +)
lOe
-Chloride ion (CI - )
Sodium chloride crystal (NaCl)
charge on the anion and a subscript for the anion that i s numerically equal to the charge on the
cation If the charges are numericall y equal, then no subscripts are necessary
Let us con s ider some examples
Potassium Bromide The potassium ion (K+) and the bromide ion (Br-) combine to form the ionic compound potassium bromide The sum of the charges is 1 + (- 1 ) = 0, so no subscripts are
nece ssary The form ula i s KEr
Zinc Iodide The z inc ion (Z n2+) and the iodide ion (r-) combine to form zinc iodid e The sum
of th e charges of one Zn 2+ ion and one 1- ion i s +2 + ( - 1) = + 1 To make the charges add up
to zero, we multiply the -1 charge of the anion by 2 and add th e s ub s cript "2" to the sy mbol for iodine Thus, the formula for zinc iodide is ZnI2
Ammonium Chloride The cation is NHt and the anion i s cr The sum of the charges is 1 +
(-1) = 0, so the ions combine in a 1: 1 ratio and the resulting formula is NH4Cl
Aluminum Oxide The cation is AI3+ and the anion is 0 2- The following diagram can be used to
determine the s ub sc ript s for this compound:
AI3+ 0 2
-The s um of the charges for aluminum oxide i s 2( + 3) + 3( - 2) = 0 Thus, the formula is A120 3
Calcium Phosphate The cation is Ca2+ and the anion is PO~- The following diagram can be used to determine the subscripts:
Ca2+
The s um of the charges i s 3(+2) + 2(-3) = 0 Thus, the formula for calcium pho s phate is
Ca 3 (P04h When we add a s ub s cript to a polyatomic ion, we must fir s t put parentheses around the
ion's formula to indicate that the s ub sc ript applies to all the atoms in the poly atomic ion
Naming Ionic Compounds
An ionic compound is named using the name of the cation followed by the name of the anion,
eliminating the word ion from each Several examples were given earlier in the Formulas of Ionic Compounds sec tion Other examples are so dium cyanide (NaCN), potassium permanganate
(KMn04), and ammonium s ulfate [(NH4hS04] Unlike the naming of molecular compounds, no
Greek prefixes are u se d For example, Li2C0 3 is lithium carbonate, not dilithium carbonate, even
though there are two lithium ions for every carbonate ion Prefixes are unnecessary because the
Trang 2•
How Are Oxoanions and Oxoacids Named?
Oxoanions are polyatomic anion s that contain one or more
oxy-gen atoms and one atom ( the "central atom") of another e lement
Examples include the chlorate (CIO } ), nitrate ( NO }), and sulfate
(SO~ - ) ions Often, two or more oxoanions have the s ame central
atom but different number s of 0 atoms (e g , NO } and N0 2)
Starting with the oxoanions who se name s end in -ate, we can
name these ion s as follows:
no n e t charge For example, the formula s of oxoacids ba se d on the nitrate (NO } ) and s ulfat e ( SO i - ) ions are HN03 and H2S04 ,
re s pectively The name s of oxoacids are derived from the names
of th e corresponding oxoanion s u s ing the following guidelines:
1 An acid ba se d on an -ate ion i s called ic acid Thus,
HCl03 i s called chloric acid
2 An acid ba se d on an -it e ion is called ous acid
Thus, HCI02 is called c hlorou s acid
1 The ion with one more 0 atom than the -at e ion i s called
the p e r ate ion Thus, CIO } is the chlorate ion , so CIO
';-is the perchlorate i o n
2 The ion with one l ess 0 atom than the -at e anion is called
the -it e ion Thu s, CI0 2 i s th e c hlorit e ion
3 Prefixes in oxoanion names are retained in the name s of the
corresponding oxoacid s Thu s, HCI04 and HCIO are called
perchloric acid and hypochlorous acid, re s pectively
3 The ion with two fewer 0 atoms than the -ate ion i s called
the hyp o ite ion Thu s, CIO - is the h ypoc hl orite ion
At a minimum, you must commit to memory the formulas
and charges of the oxoanions whose name s end in -at e so that
you can apply these guidelines when nece ssary
Many oxoacids, s uch as H2S04 and H3P04 , are
polyprotic-meaning that they have more than one ionizable hydrogen atom
In the se cases, th e name s of anions in which one or more (but not all ) of the hydrogen ion s have been removed must indicate the number of H ion s that remain, a s s hown for the anion s derived
from pho s phoric acid:
In addition to the simple acid s di s cu sse d in Section 2.6, there
is another important cla ss of acid s known as oxoacids, which
ion-ize to produce hydrogen ions and the corresponding oxoa nion s
The formula of an oxoacid can be determined by adding enough
H + ions to the corre s ponding oxoanion to yield a formula with
H y drogen phosphate ion
Phosphate ion
Strategy Each species is either an oxoanion or an oxoacid Identify the "reference oxoanion" (the
one with the -ate ending) for each, and apply the rules to determine appropriate names
Setup (a) Chlorine, bromine, and iodine (members of group 7 A) all form analogous series of
oxoanions with one to four oxygen atoms Thus, the reference oxoanion is bromate (BrO :;-), which
is analogous to chlorate (ClO:;-) In parts (b) and (c), HCO:;- and H2C0 3 have one and two more
hydrogens, respectively, than the carbonate ion (Co j- )
Solution (a) BrO; has one more 0 atom than the bromate ion (BrO:;-), so Br0 4 is the perbromate
ion (b) coj- is the carbonate ion Because HCO :;- has one ionizable hydrogen atom, it is called the
hydrogen ca rbonat e i on (c) With two ionizable hydrogen atoms and no charge on the compound,
H2C03 is ca rbonic acid
Practice Problem A Name the following species: (a) HErO, (b) HS04 , and (c) H2C20 4
Practice Problem B Name the following species: (a) HI03, (b) HCr0 4, and (c) HC20 ;
~I -~"
Determine the formula of sulfurous acid
Strategy The -ous ending in the name of an acid indicates that the acid is derived from an oxoanion
ending in -it e Determine the formula and charge of the oxoanion, and add enough hydrogens to
make a neutral formula
Setup The sulfite ion is SO j-
Solution The formula of sulfurous acid is H2S03
Practice Problem A Determine the formula of perbromic acid (Refer to the information in Sample
Problem 2.7.)
Practice Problem B Determine the formula of chromic acid
59
Trang 360 CHAPTER 2 Atoms, Molecules, and Ions
Figure 2.16 Steps for naming
molecular and ionic compounds
Think About It Be careful not to
confuse the subscript in a formula
with the charge on the metal ion In
part (c), for example, the subscript
on Fe is 2, but this is an iron (III)
polyatomic
s! Z s ."z
Cation ha s Cation ha s more
a ni y one charg e than one charge
• Alkali metal cation s • Other metal cation s
• A I kal i n e earth metal
in parenthese s
• If monatomi c anion, add -ide to ro o t of element name
• If po lyatomic anion , use name of anion
ions have known charges Lithium ion always has a charge of + 1, and carbonate ion always has
a charge of -2 The only ratio in which they can combine to form a neutral compound is two Li +
ions for every one CO ~ - ion Therefore, the name lithium carbonate is sufficient to convey the compound's empirical formula
In cases where a metal cation may have more than one possible charge, recall that the charge
is indicated in the name of the ion with a Roman numeral in parentheses Thus, the compounds
FeCI2 and FeCI3 are named iron ( Il ) chloride and iron(IIl) chlorid e , respectively (These are pro
-nounced "iron - two chloride" and "iron - three chloride.") Figure 2.16 summarizes the steps for naming molec u lar and ionic compounds
Sample Problem s 2.9 and 2.10 illustrate how to name ionic compounds and write formulas for ionic compounds based on the information given in Figure 2.16 and Tables 2.8 and 2.9
Sample Problem 2.9
Name the following ionic compounds: (a) MgO, (b) AI(OH)3' and (c) FeiS04h
Strategy Begin by identifying the cation and the anion in each compound, and then combine the names for each, eliminating the word i O I1
Setup MgO contains Mg2+ and 0 2- , the magnesium ion and the oxide ion; AI(OH)3 contains Al3+
and OH- , the aluminum ion and the hydroxide ion; and Fe2(S04)3 contains Fe3+ and SO ~ - , the iron (III) ion and the sulfate ion We know that the iron in F~(S0 4 ) 3 is iron(III), Fe3+, because it is combined with the sulfate ion in a 2:3 ratio
Solution (a) Combining the cation and anion names, and eliminating the word ion from each of the individual ions' names, we get magn e sium oxide as the name of MgO; (b) AI(OH)3 is aluminum
h y droxide; and (c) Fe2(S04)3 is iron ( J/l) sulfate
Practice Problem A Name the following ionic compounds: (a) Na2S04, (b) Cu(N03)2,
(c) Fe2(C03h
Practice Problem B Name the following ionic compounds: (a) K2Cr20 7, (b) Li2C20 4, (c) CuN03
Trang 4SECTION 2.7 Ions and Ionic Compounds 61
Deduce the formulas of the following ionic compounds: (a ) mercury ( I ) chloride , ( b ) lead ( II )
chromate, and (c) potassium hydrogen pho s phate
Strategy Identify the ions in each compound, and determine their ratio s of combination using the
charges on the cation and anion in each
Setup (a) Mercury(I) chloride is a combination of Hg ~ + and CI - [Mercury ( I ) i s one of the few
cations listed in Table 2.9.] In order to produce a neutral compound , the s e two ion s must combine in
a 1:2 ratio (b) Lead(II) chromate is a combination of Pb 2+ and CrO ~ - These ion s combine in a 1: 1
ratio (c) Potassium hydrogen phosphate i s a c ombination of K + and HPO~- The s e ions combine in
a 2: 1 ratio
I Solution The formulas are (a) Hg2Clb (b) PbCr0 4 , and ( c ) K2HP04·
Practice Problem A Deduce the formulas of the following ionic compound s : ( a) lead(II) chloride,
(b) magnesium carbonate, and (c) ammonium phosphate
Practice Problem B Deduce the formula s of the following ionic compounds: ( a ) iron ( III ) sulfide,
(b) mercury(II) nitrate, and (c) potassium s ulfite
~ -~
Hydrates
Hydrates are compounds that have a specific number of water molecules within their solid
struc-ture In its normal state, for example, each unit of copper(II) sulfate has five water molecules
asso-ciated with it The systematic name for this compound is copper(II) sulfate pentahydrate , and its
f ormula is written as CUS04 SH 2 0 The water molecules can be driven off by heating When this
o ccurs, the resulting compound is CUS04, which is sometimes called anhydrous copper(II ) sulfate;
a nhydrous means that the compound no longer has water molecules a s sociated with it Hydrates
and the corresponding anhydrous compounds often have distinctly different physical and chemical
Familiar Inorganic Compounds
So me compounds are better known by their common names than by their systematic chemical
n a mes Familiar examples are listed in Table 2.10
Think About It Make sure that the
charges s um to zero in each compound formula In part (a), for example,
Hg ~ + + 2Cl- = ( 2+ ) + 2 (- 1 ) = 0;
in part (b), (+ 2) + ( - 2 ) = 0; and in
part ( c ), 2(+1) + (-2) = O
Figure 2 17 CUS04 is white The
pentahydrate, CUS04 5H20, is blue
Trang 562 CHAPTER 2 Atoms, Molecules, and Ions
Formula
H20
NH 3
CO2 NaCI
N20
CaC03 NaHC03 MgS04 ·7H20
Mg(OHh
Common Name
Water Ammonia Dry ice Salt
Laughing gas Marble, chalk, limestone Baking soda
Epsom salt
Milk of magnesia
Systematic Name
Dihydrogen monoxide Trihydrogen nitride
Solid carbon dioxide Sodium chloride
Dinitrogen monoxide Calcium carbonate
Sodium hydro gen carbonate Magnesium sulfate heptahydrate Magnesium hydroxide
Checkpoint 2.7 Ions and Ionic Compounds
c) Lead(II) sulfate
d) Monolead sulfate e) Lead monosulfate
What is the correct formula for the
compound iron (ill) carbonate?
Which of the following is the correct
formula for nitrous acid?
a) HNO
b) HN20 c) N20
c) Na3N d) NaN03
e) NaN02
What is the correct name of the compound Hg2Cr04?
a) Mercury(I) chromate b) Mercury(II) chromate c) Mercury dichromate
d) Dimercury chromate e) Monomercury chromate
Trang 6APPLYING WHAT YOU'VE LEARNED 63
Applying What You've Learned
Although iron is an essential element, it is also a potentially toxic substance
Hemochromato-sis is one of the most common hereditary disorders, causing "iron overload" or the storage of
excess iron in the tissues and organs Individuals with hemochromatosis often must undergo
periodic phlebotomy (removal of blood) in order to remove excess stored iron, which would
otherwise cause irreversible damage to internal organs including the liver and kidneys Those
who have a tendency to store too much iron are advised to avoid combining iron-rich foods
with substances that enhance iron absorption, such as ascorbic acid (vitamin C)
Because of iron's toxicity, iron supplements are potentially dangerous, especially
to children In fact, iron poisoning is the most common toxicological emergency in
young children due in part to the resemblance many iron supplements bear to candy
Most vitamins that contain iron are sold with childproof caps to help prevent accidental
overdose The Food and Drug Administration (FDA) requires supplements containing
more than 30 mg of iron per dose to be sold in single-dose blister packs to make it more
difficult for a child to consume a dangerous amount
Problems:
a) Iron has four naturally occurring isotopes: 54Fe (53.9396 amu), 56Fe
(55.9349 amu), 57Fe (56.9354 amu), and 58Fe (57 9333 amu) For each isotope,
detennine the number of neutrons in the nucleus [ ~~ Sample Problem 2.1]
b) Calculate the average atomic mass of iron given that the natural abundances of the
four isotopes are 5 845, 91.754, 2.119, and 0.282 percent, respectively
[ ~~ Sample Problem 2.2]
c) Write the molecular formula for ascorbic acid (see the ball-and - stick model)
[ ~~ Sample Problem 2.3]
d) DeteIlIIine the empirical fOImula of ascorbic acid [ ~~ Sample Problem 2.6]
e) Write the fOIIllula for ferrous sulfate [iron (II) sulfate] [ ~ Sample Problem 2.10]
•
Trang 764 CHAPTER 2 Atoms, Molecules, and Ions
CHAPTER SUMMARY
Section 2.1
o Dalton's atomic theory states that all matter is made up of tiny
indivisible, immutable particles called atoms Compounds form,
moreover, when atoms of different elements combine in fixed ratios
According to the law of definite proportions, any sample of a given
compound will always contain the same elements in the same mass
ratio
o The law of multiple proportions states that if two elements can form
more than one compound with one another, the mass ratio of one will
be related to the mass ratio of the other by a small whole number
o The law of conservation of mass states that matter can be neither
created nor destroyed
Section 2.2
o On the basis of Dalton's atomic theory, the atom is the basic unit of
an element Studies with radiation indicated that atoms contained
subatomic particles, one of which was the electron
o Experiments with radioactivity have shown that some atoms give off
different types of radiation, called alpha (ex) rays, beta (f3) rays, and
gamma (y) rays Alpha rays are composed of ex particles, which are
actually helium nuclei Beta rays are composed of f3 particles, which
are actually electrons Gamma rays are high-energy radiation
o Most of the mass of an atom resides in a tiny, dense region known as
the nucleus The nucleus contains positively charged particles called
protons and electrically neutral particles called neutrons Protons
and neutrons are referred to collectively as nucleons The charge on a
proton is equal in magnitude but opposite in sign to the charge on an
electron The electrons occupy the relatively large volume around the
nucleus A neutron has a slightly greater mass than a proton, but each
is almost 2000 times as massive as an electron
Section 2.3
o The atomic number (Z) is the number of protons in the nucleus of
an atom The atomic number determines the identity of the atom
The mass number (A) is the sum of the protons and neutrons in the
nucleus
o Atoms with the same atomic number but different mass numbers are
called isotopes
Section 2.4
o The periodic table arranges the elements in rows (periods) and
columns (groups orfamilies) Elements in the same group exhibit
similar properties
o All elements fall into one of three categories: nonmetal, metal, or
metalloid
o Some of the groups have special names including alkali metals
(Group lA, except hydrogen), alkaline earth metals (Group 2A),
chalcogens (Group 6A), halogens (Group 7A), noble gases (Group
8A), and transition elements or transition metals (Group IB and
Groups 3B-8B)
Section 2.5
o Atomic mass is the mass of an atom in atomic mass units One atomic
mass unit (amu), is exactly one-twelfth the mass of a carbon-12 atom
o The periodic table contains the average atomic mass (sometimes
called the atomic weight) of each element
Section 2.6
o A molecule is an electrically neutral group of two or more atoms
Molecules consisting of just two atoms are called diatomic
Diatomic molecules may be homonuclear (just one kind of atom) or
heteronuclear (two kinds of atoms) In general, molecules containing more than two atoms are called polyatomic
o A chemical formula denotes the composition of a substance A
molecular formula specifies the exact numbers of atoms in a molecule
of a compound A structural formula shows the arrangement of atoms
in a substance
o An allotrope is one of two or more different forms of an element
o Molecular compounds are named according to a set of rules, including
the use of Greek prefixes to specify the number of each kind of atom
in the molecule
o Binary compounds are those that consist of two elements An acid is
a substance that generates hydrogen ions when it dissolves in water
An ionizable hydrogen atom is one that can be removed in water to become a hydrogen ion, H +
o Inorganic compounds are generally those that do not contain carbon
Organic compounds contain carbon and hydrogen, sometimes
in combination with other elements Hydrocarbons contain only carbon and hydrogen The simplest hydrocarbons are the alkanes A
functional group is a group of atoms that determines the chemical properties of an organic compound
o Empiricalformulas express, in the smallest possible whole numbers,
the ratio of the combination of atoms of the elements in a compound The empirical and molecular formulas of a compound mayor may not
be identical
Section 2.7
o An ion is an atom or group of atoms with a net charge An atomic ion
or a monatomic ion consists of just one atom
o An ion with a net positive charge is a cation An ion with a net
negative charge is an anion An ionic compound is one that consists
of cations and anions in an electrically neutral combination A dimensional array of alternating cations and anions is called a lattice
three-o Ionic compounds are named using rules similar to those for molecular
compounds In general, prefixes are not used to denote the number of ions in the names of ionic compounds
o Polyatomic ions are those that contain more than one atom chemically
bonded together Oxoanions are polyatomic ions that contain one or more oxygen atoms
o Oxoacids are acids based on oxoanions Acids with more than one
ionizable hydrogen atom are called polyprotic
o Hydrates are compounds whose formulas include a specific number of
water molecules
Trang 8Empirical formula, 51 Family, 44
Functional group, 51 Gamma ('I) rays, 39 Group, 44
Halogens, 45 Heteronuclear, 48 Homonuclear, 48 Hydrate, 61
Hydrocarbon, 51 Inorganic compounds, 51 Ion, 55 ,
QUESTIONS AND PROBLEMS
QUESTIONS AND PROBLEMS
Ionic compound, 55 Ionizable hydrogen atom, 51 Isotope, 41
Lattice, 57 Law of conservation of mass, 36 Law of definite proportions, 35 Law of multiple proportions, 35 Mass number (A), 40
Metal, 44 Metalloid, 44 Molecular formula, 48 Molecule, 47
Monatomic ion, 55 Neutron, 40
Noble gases, 45 Nonmetal, 44 Nucleons, 41
-Nucleus, 40 Organic compounds, 51 Oxoacid, 59
Oxoanion, 59 Period, 44
Periodic table, 44 Poly atomic ion, 56 Polyatomic molecule, 48 Polyprotic acid, 59
Proton, 40 Radiation, 36 Radioactivity, 38 Structural formula, 48 Transition elements, 45 Transition metals, 45
2.2 State the laws of definite proportions and multiple proportions
lllustrate each with an example
.7 Describe the experimental basi!> for believing that the nucleus
occupies a very small fraction of the volume of the atom
P roblems
The diameter of a neutral helium atom is about 1 X 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 1 cm from end to end?
•
2.9 Roughly speaking, the radius of an atom is about 10,000 times
greater than that of its nucleus If an atom were magnified so that the radius of its nucleus became 2.0 cm, about the size of a marble, what would be the radius of the atom in miles?
Why do all atoms of an element have the same atomic number, although they may have different mass numbers?
What do we call atoms of the same elements with different mass numbers?
Explain the meaning of each term in the symbol1X
Calculate the number of neutrons of 239Pu
For each of the following species, determine the number of protons and the number of neutrons in the nucleus: ~He, iHe,
2I2Mg, 12 g, 4 25M 422 1, 8T' 739B 195 r, 758 Pt Indicate the number of protons, neutrons, and electrons in each of
th I I ' e 10 owrng species: 157 N , 16 ,233S 69 3C u, 8438 S I30B r, 56 a, 174 86W , 2800 g 2H
Trang 966
2.18
CHAPTER 2 Atoms, Molecules, and Ions
Write the appropriate symbol for each of the following isotopes: (a) Z = 11, A = 23; (b) Z = 28, A = 64, (c) Z = 50, A = 115,
2.19 Write the appropriate symbol for each of the following isotopes:
(a) Z = 74, A = 186; (b) Z = 80, A = 201, (c) Z = 34, A = 76, (d) Z = 94, A = 239
2.20 Determine the mass number of (a) a boron atom with 5 neutrons,
46 neutrons, and (d) a mercury atom with 116 neutrons
2.21 Determine the mass number of (a) a fluorine atom with 10
neutrons, (b ) a sulfur atom with 18 neutrons, (c) an arsenic atom with 42 neutrons, and (d) a platinum atom with 114 neutrons
2.22 The following radioactive isotopes are used in medicine for
imaging organs, studying blood circulation, treating cancer, and so on Give the number of neutrons present in each isotope:
State two differences between a metal and a nonmetal
Write the names and symbols for four elements in each of the following categories: (a) nonmetal, (b) metal, (c) metalloid
Give two examples of each of the following: (a) alkali metals,
(b) alkaline earth metals, (c) halogens, (d) noble gases, ( e) chalcogens, (f) transition metals
The explosion of an atomic bomb in the atmosphere releases many radioactive isotopes into the environment One of the
isotopes is 9OSr Via a relatively short food chain, it can enter the human body Considering the position of strontium in the periodic table, explain why it is particularly harmful to humans
Problems
2.28 Elements whose names end with - ium are usually metals; sodium
is one example Identify a nonmetal whose name also ends with
•
-tum
2.29 Describe the changes in properties (from metals to nonmetals or
from nonmetals to metals) as we move (a) down a periodic group
2.30 Consult a handbook of chemical and physical data (ask your
instructor where you can locate a copy of the handbook) to find (a) two metals less dense than water, (b) two metals more dense than mercury, (c) the densest known solid metallic element, and (d) the densest known solid nonmetallic element
2.31 Group the following elements in pairs that you would expect to
show similar chemical properties: K, F, P, Na, Cl, and N
2.32
2.33
Group the following elements in pairs that you would expect to
show similar chemical properties: I, Ba, 0, Br, S, and Ca
Write the symbol for each of the following biologically important elements in the given periodic table: iron (present
in hemoglobin for transporting oxygen), iodine (present in the thyroid gland), sodium (present in intracellular and extracellular
fluids), phosphorus (present in bones and teeth), sulfur (present in proteins), and magnesium (present in chlorophyll molecules)
Explain clearly what is meant by the statement "The atomic mass
of gold is 197.0 amu."
2.37 What information would you need to calculate the average
atomic mass of an element?
Problems
2.38 The atomic masses of n Cl (75.53 percent) and n Cl (24.47
percent) are 34.968 and 36.956 amu, respectively Calculate the average atomic mass of chlorine The percentages in parentheses denote the relative abundances
2.39 The atomic masses oe04Pb (1.4 percent), 206Pb (24.1
percent),207Pb (22.1 percent), and 208Pb (52.4 percent) are 203.973020, 205.974440,206.975872, and 207.976627 amu, respectively Calculate the average atomic mass of lead The percentages in parentheses denote the relative abundances
2.40 The atomic masses of 203Tl and 20sTI are 202.972320 and
204.974401 amu, respectively Calculate the natural abundances
of these two isotopes The average atomic mass of thallium is 204.4 amu
2.41 The atomic masses of 6Li and 7Li are 6.0151 amu and
7.0160 amu, respectively Calculate the natural abundances of these two isotopes The average atomic mass of Li is 6.941 amu 2.42 What is the mass in grams of 13.2 amu?
2.43 How many atomic mass units are there in 8.4 g?
Section 2.6: Molecules and Molecular Compounds
Review Questions
2.44 2.45
What is the difference between an atom and a molecule? What are allotropes? Give an example How are allotropes different from isotopes?
Trang 102.46
2.47
Describe the two commonly used molecular models
What does a chemical formula represent? Determine the ratio of the atoms in the following molecular formulas: (a) NO, (b) NCI3, (c) N20 4, (d) P406
2.48 Define molecular formula and empirical formula What are the
similarities and differences between the empirical formula and molecular formula of a compound?
2.49 Give an example of a case in which two molecules have different
molecular formulas but the same empirical formula
2.50 What is the difference between inorganic compounds and organic
compounds?
2.51 Give one example each for a binary compound and a ternary
compound (A ternary compound is one that contains three
differen t elements.)
2.52 Explain why the formula HCl can represent two different
chemical systems
Problems
2.53 For each of the following diagrams, determine whether it
represents diatomic molecules, poly atomic molecules, molecules that are not compounds, molecules that are compounds, or an
elemental form of the substance
_.54 For each of the following diagrams, determine whether it
represents diatomic molecules, polyatomic molecules, molecules that are not compounds, molecules that are compounds, or an
elemental form of the substance
~ L "
1 _ 57
: -8
Identify the following as elements or compounds: NH3, N2 , S8,
NO, CO, COlo Hz, SOz·
Give two examples of each of the following: (a) a diatomic
molecule containing atoms of the same element, (b) a diatomic
molecule containing atoms of different elements, (c) a polyatomic molecule containing atoms of the same element, (d) a polyatomic molecule containing atoms of different elements
Write the empirical formulas of the following compounds:
(a) CzNz, (b) C6H6, (c) C9H2o, (d) P40 lO, (e) BzH6
Write the empirical formulas of the following compounds:
(a) A12Br6, (b) Na2SZ04, (c)NzOs, (d)K2Cr207
QUESTIONS AND PROBLEMS
Write the molecular formula of alanine, an amino acid used
in protein synthesis The color codes are black (carbon), blue
(nitrogen), red (oxygen), and white (hydrogen)
Write the molecular formula of ethanol The color codes are:
black (carbon), red (oxygen), and white (hydrogen)
Name the following binary molecular compounds: (a) NCI3,
(b) IF7, (c) P406, (d) S2C12
67
Write chemical formulas for the following molecular compounds:
(a) phosphorus tribromide, (b) dinitrogen tetrafluoride, (c) xenon
tetroxide, (d) selenium trioxide
Write the molecular formulas and names of the following
Give an example of each of the following: (a) a monatomic
cation, (b) a monatomic anion, (c) a poly atomic cation, (d) a
poly atomic anion
What is an ionic compound? How is electrical neutrality maintained in an ionic compound?
Explain why the chemical formulas of ionic compounds are
usually the same as their empirical formulas
What is the Stock system? What are its advantages over the older
system of naming cations?
Trang 1168 CHAPTER 2 Atoms, Molecules, and Ions
Problems
2.69 Give the number of protons and electrons in each of the following
+ C 2+ 13+ F ' + 1 - F- S 2- 0 2- N3
-common IOns: Na, a , A , e- , , , , ,
2.70 Give the number of protons and electrons in each of the following
+ 2+ F 3+ B - M 2+ C4- C 2+
common IOns: K , Mg , e , r, n , , u
2.71 Write the formulas for the following ionic compounds:
(a) sodium oxide, (b) iron sulfide (containing the Fe2+ ion), (c) cobalt sulfate (containing the C03+ and SO~- ions),
(d) barium fluoride
2.72 Write the formulas for the following ionic compounds: (a)
copper bromide (containing the Cu+ ion), (b) manganese oxide
(containing the Mn3+ ion), (c) mercury iodide (containing the Hgi+ ion), (d) magnesium phosphate (containing the PO ~ - ion)
2.73 Which of the following compounds are likely to be ionic? Which
are likely to be molecular? SiCI4, LiF, BaClb B2H6, KCl, C2H4
2.74 Which of the following compounds are likely to be ionic? Which
are likely to be molecular? CH4, NaBr, BaFb CCI4, ICl, CsCl,
NF 3
2.75 Name the following compounds: (a) KH2P04, (b) K 1 HP0 4 ,
(m) Al(OH)3'
2.76 Name the following compounds: (a) KCIO, (b) Ag2C03,
(c) HNOz, (d) KMn04, (e) CsCI03, (f) KNH4S04, (g) FeO,
(h) Fez03' (i) TiCI4 , (j) NaH, (k) Li3N, (1) Na20, (m) Na20Z'
2.77 Write the formulas for the following compounds: (a) rubidium
nitrite, (b) potassium sulfide, (c) sodium hydrogen sulfide, (d) magnesium phosphate, (e) calcium hydrogen phosphate,
(f) potassium dihydrogen phosphate, (g) iodine heptafluoride,
(h) ammonium sulfate, (i) silver perchlorate, (j) boron trichloride
2.78 Write the formulas for the following compounds: (a) copper(I)
cyanide, (b) strontium chlorite, (c) perbromic acid, (d)
hydroiodic acid, (e) disodium ammonium phosphate, (f) lead(II)
carbonate, (g) tin(II) fluoride, (h) tetraphosphorus decasulfide,
(i) mercury(II) oxide, G) mercury(I) iodide, (k) selenium hexafluoride
2.79 In the diagrams shown here, match each of the drawings with
the following ionic compounds: A1 2 0 3 , LiH, Na2S, Mg(N03h (Green spheres represent cations and red spheres represent
anions.)
2.80 Given the formulas for the ionic compounds, draw the correct
ratio of cations to anions as shown in Problem 2.79: (a) BaS04, (b) CaF2, (c) Mg3N2, (d) K20
Additional Problems
2.81 Define the following terms: acids, bases, oxoacids, oxoanions,
and hydrates
2.82 A sample of a uranium compound is found to be losing mass
gradually Explain what is happening to the sample
2.83 In which one of the following pairs do the two species resemble
each other most closely in chemical properties: (a) : Hand: H+,
(b) liN and Ij N3- , (c) I ~C and I~C? Explain
2.84 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
2.85 One isotope of a nonmetallic element has mass number 127 and
74 neutrons in the nucleus The anion derived from the isotope has 54 electrons Write the symbol for this anion
2.86 The following table gives numbers of electrons, protons, and
neutrons in atoms or ions of a number of elements Answer the following: (a) Which of the species are neutral? (b) Which are
negatively charged? (c) Which are positively charged? (d) What are the conventional symbols for all the species?
Atom or Ion of Element
2.88 The following phosphorus sulfides are known: P4S3, P4S7, and
P4S IO Do these compounds obey the law of mUltiple proportions?
2.89 Which of the following are elements, which are molecules but
not compounds, which are compounds but not molecules, and which are both compounds and molecules? (a) SOb (b) S8,
(c) Cs, (d) N 2 0 S' (e) 0, (f) Oz, (g) 0 3, (h) CH4, (i) KEr, ( j) S,
2.90 What is wrong with the name (given in parentheses or brackets)
for each of the following compounds: (a) BaClz (barium
dichloride), (b) Fe203 [iron(ll) oxide], (c) CsN02 (cesium
nitrate), (d) Mg(HC03h [magnesium(ll) bicarbonate]?
2.91 Discuss the significance of assigning an atomic mass of exactly
12 amu to the carbon-12 isotope
2.92 Determine what is wrong with the chemical formula and
write the correct chemical formula for each of the following compounds: (a) (NH3) 2C03 (ammonium carbonate), (b) CaOH
(zinc dichromate)
2.93 Fill in the blanks in the table:
2.94 (a) Which elements are most likely to form ionic compounds?
(b) Which metallic elements are most likely to form cations with different charges?
2.95 Write the formula of the common ion derived from each of the
following: (a) Li, (b) S, (c) I, (d) N, (e) AI, (f) Cs, (g) Mg
2.96 Which of the following symbols provides more information about
the atom: 23Na or IINa? Explain
Trang 12elements in Groups 3A, 4A, SA, and 6A
Determine the molecular and empirical formulas of the compounds shown here (Black spheres are carbon, and white
spheres are hydrogen.)
For the noble gases (the Group 8A elements) i He, igNe, i~Ar,
~~Kr, and 1~~Xe, (a) determine the number of protons and neutrons in the nucleus of each atom, and (b) determine the ratio
of neutrons to protons in the nucleus of each atom Describe any
general trend you discover in the way this ratio changes with
increasing atomic number
2.100 List the elements that exist as gases at room temperature (Hint:
Most of these elements can be found in Groups SA, 6A, 7 A,
and 8A.)
2.101 The Group IB metals, Cu, Ag, and Au, are called coinage metals
What chemical properties make them especially suitable for
making coins and jewelry?
2.102 The elements in Group 8A of the periodic table are called noble
gases Can you suggest what "noble" means in this context?
2.103 The formula for calcium oxide is CaO What are the formulas for
magnesium oxide and strontium oxide?
2.104 A common mineral of barium is barytes, or barium sulfate
(BaS04) Because elements in the same periodic group have
similar chemical properties, we might expect to find some radium sulfate (RaS04) mixed with barytes since radium is the last member of Group 2A However, the only source of radium compounds in nature is in uranium minerals Why?
after people, (c) named after a color (Consult http://www
Google.com, http://www.Wikipedia.com, or http://www
Webelements.com.)
2 106 Name the only country that is named after an element (Hint:
This country is in South America.)
hydrogen fluoride (HF) and deuterium fluoride (DF), where deuterium (TH) is an isotope of hydrogen Would a given anlOunt
of fluorine react with different masses of the two hydrogen isotopes? Does this violate the law of definite proportion? Explain
2.108 Predict the formula and name of a binary compound formed from
the following elements: (a) Na and H, (b) Band 0, (c) Na and S,
(d) Al and F, (e) F and 0 , (f) Sr and Cl
anion contains 36 electrons, (b) a radioactive noble gas with
86 protons, (c) a Group 6A element whose anion contains 36 electrons, (d) an alkali metal cation that contains 36 electrons,
(e) a Group 4A cation that contains 80 electrons
2.110 Show the locations of (a) alkali metals, (b) alkaline earth metals,
(c) the halogens, and (d) the noble gases in the given outline of
a periodic table Also draw dividing lines between metals and metalloids and between metalloids and nonmetals
3B 4B SB 6B 7B I 8B liB 2B
2.111 Fill in the blanks in the table
Magnesium bicarbonate SrCl2
Manganese(II) chlorate SnBr4
by their systematic chemical names Give the chemical formulas
of the following substances: (a) Dry ice, (b) salt, (c) laughing gas,
(d) marble (chalk, limestone), (e) baking soda, (f) ammonia,
(g) water, (h) milk of magnesia, (i) epsom salt
2.113 On page 36 it was pointed out that mass and energy are alternate
aspects of a single entity called mass-energy The relationship between these two physical quantities is Einstein's equation,
E = me 2 , where E is energy, m is mass, and e is the speed of light In a combustion experiment, it was found that 12.096 g
of hydrogen molecules combined with 96.000 g of oxygen molecules to form water and released l.71S X 103 kJ of heat
Use Einstein's equation to calculate the corresponding mass
change in this process, and comment on whether or not the law of
conservation of mass holds for ordinary chemical processes
2.114 (a) Describe Rutherford's experiment and how the results
revealed the nuclear structure of the atom (b) Consider the
23Na atom Given that the radius and mass of the nucleus are
3.04 X 10- 15 m and 3.82 X 10- 23 g, respectively, calculate the density of the nucleus in g/cm3 The radius of a 23Na atom is
186 pm Calculate the density of the space occupied by the
electrons outside the nucleus in the sodium atom Do your results
support Rutherford's model of an atom? [The volume of a sphere
of radius r is 1 'ITr 3 .]
2.115 Draw all possible structural formulas of the following
hydrocarbons: CH4, C Z H 6, C3Hs, C4H IO , and C S H I 2 •
Trang 1370 CHAPTER 2 Atoms, Molecules, and Ions
2.116 Draw two different structural formulas based on the molecular
formula C2H60 Is the fact that you can have more than one compound with the same molecular formula consistent with Dalton's atomic theory?
2.117 Ethane and acetylene are two gaseous hydrocarbons Chemical
analyses show that in one sample of ethane, 2.65 g of carbon are combined with 0.665 g of hydrogen, and in one sample
of acetylene, 4.56 g of carbon are combined with 0.383 g of hydrogen (a) Are these results consistent with the law of multiple proportions? (b) Write reasonable molecular formulas for these compounds
2.118 A cube made of platinum (Pt) has an edge length of 1.0 cm
(a) Calculate the number of Pt atoms in the cube (b) Atoms are
spherical in shape Therefore, the Pt atoms in the cube cannot fill all the available space If only 74 percent of the space inside the cube is taken up by Pt atoms, calculate the radius in picometers
of a Pt atom The density Pt is 21.45 g/cm3 , and the mass of a single Pt atom is 3.240 X 10 - 22 g [The volume of a sphere of radius r is ~1Tr3.l
2.119 A monatomic ion has a charge of + 2 The nucleus of the parent
atom has a mass number of 55 If the number of neutrons in the nucleus is 1.2 times that of the number of protons, what is the name and symbol of the element?
2.120 In the following 2 X 2 crossword, each letter must be correct
in four ways: horizontally, vertically, diagonally, and by itself
When the puzzle is complete, the four spaces will contain the
overlapping symbols of 10 elements Use capital letters for each
square There is only one correct solution
A colorless gaseous nonmetal
An element that makes fireworks green
An element that has medicinal uses
Diagonal
1-4: Two-letter symbol for an element used in electronics 2-3: Two-letter symbol for a metal used with Zr to make
wires for superconducting magnets
2.121 Name the given acids
PRE-PROFESSIONAL PRACTICE EXAM PROBLEMS:
PHYSICAL AND BIOLOGICAL SCIENCES
Carbon-14, a radioactive isotope of carbon, is used to determine the ages
of fossils in a technique called carbon dating Carbon-14 is produced in
the upper atmosphere when nitrogen-14 atoms are bombarded by neutrons
from cosmic rays 14C undergoes a process called f3 emission in which a
neutron in the nucleus decays to form a proton and an electron The
elec-tron, or f3 particle, is ejected from the nucleus Because the production and
decay of 14C occur simultaneously, the total amount of 14C in the
atmo-sphere is constant Plants absorb 14C in the form of CO2 and animals
con-sume plants and other animals Thus, all living things contain a constant
ratio of 12C to 14c When a living thing dies, the 14C it contains continues
to decay but because replenishment ceases, the ratio of 12C to 14C changes
over time Scientists use the 12C to 14C ratio to determine the age of
mate-rial that was once living
1 If atmospheric conditions were to change such that 14C were
produced at twice the current rate,
a) the world's supply of 14N would be consumed completely
b) the 12C to 14C ratio in living things would increase
c) the 12C to 14C ratio in living things would decrease
d) the 12C to 14C ratio in living things would not change
2 When a 14N nucleus is bombarded by a neutron to produce a 14C
nucleus, what else is produced?
a) Nothing b) Another neutron c) An electron
d) A proton
3 Based on the description of f3 emission in the passage, what nucleus
results from the decay of a 14C nucleus by f3 emission?
a) 14N
b) 1 3 N
c) 12C
d) 13C
4 The accuracy of carbon dating depends on the assumption that
a) 14C is the only radioactive species in the material being tested
b) the rate of decay of 14C is constant
c) 12C and 14C undergo radioactive decay at the same rate
d) each 14C nucleus decays to give a 12C nucleus