Selected Exercise Chemistry_The Central Science
Atoms, Molecules, and Ions
2.1 A charged particle is caused to move between two electrically
charged plates, as shown below.
(a) Why does the path of the charged particle bend?
(b) What is the sign of the electrical charge on the particle?
(c) As the charge on the plates is increased, would
you expect the bending to increase, decrease, or stay the
same? (d) As the mass of the particle is increased while
the speed of the particles remains the same, would you
expect the bending to increase, decrease, or stay the
same? [Section 2.2]
2.4 Does the following drawing represent a neutral atom or
an ion? Write its complete chemical symbol including
mass number, atomic number, and net charge (if any).
[Sections 2.3 and 2.7]
2.6 Write the chemical formula for the following compound.
Is the compound ionic or molecular? Name the
compound. [Sections 2.6 and 2.8]
2.9 How does Dalton's atomic theory account for the fact
that when 1.000 g of water is decomposed into its elements,
0.111 g of hydrogen and 0.889 g of oxygen are obtained
regardless of the source of the water?
2.11 A chemist finds that 30.82 g of nitrogen will react with
17.60 g, 35.20 g, 70.40 g, or 88.00 g of oxygen to form
four different compounds. (a) Calculate the mass of oxygen
per gram of nitrogen in each compound. (b) How
do the numbers in part (a) support Dalton's atomic
2.13 Summarize the evidence used by J. J. Thomson to argue
that cathode rays consist of negatively charged
2.15 (a) Figure 2.5 shows the apparatus used in the Millikan
oil-drop experiment with the positively charged plate
above the negatively charged plate. What do you think
would be the effect on the rate of oil drops descending if
the charges on the plates were reversed (negative above
positive)? (b) In his original series of experiments, Millikan
measured the charge on 58 separate oil drops.
Why do you suppose he chose so many drops before
reaching his final conclusions?
2.17 The radius of an atom of krypton (Kr) is about 1.9 A.
(a) Express this distance in nanometers (nm) and in picometers
(pm). (b) How many krypton atoms would
have to be lined up to span 1.0 mm? (c) If the atom is assumed
to be a sphere, what is the volume in cm3 of a single
2.19 Answer the following questions without referring to
Table 2.1: (a) What are the main subatomic particles
that make up the atom? (b) What is the relative charge
(in multiples of the electronic charge) of each of the particles?
(c) Which of the particles is the most massive?
(d) Which is the least massive?
2.21 (a) Define atomic number and mass number. (b) Which
of these can vary without changing the identity of the
2.23 How many protons, neutrons, and electrons are in the
following atoms: (a) 40 Ar, (b) 65Zn, (c) 70Ga, (d) 80Br,
(e) 184W, (f) 243 Am?
2.25 Fill in the gaps in the following table, assuming each
column represents a neutral atom:
Write the correct symbol, with both superscript and subscript,
for each of the following. Use the list of elements
inside the front cover as needed: (a) the isotope of platinum
that contains 118 neutrons, (b) the isotope of krypton
with mass number 84, (c) the isotope of arsenic with
mass number 75, (d) the isotope of magnesium that has
an equal number of protons and neutrons.
2.29 (a) What isotope is used as the standard in establishing
the atomic mass scale? (b) The atomic weight of boron is
reported as 10.81, yet no atom of boron has the mass of
10.81 amu. Explain.
2.31 Only two isotopes of copper occur naturally, 63Cu
(atomic mass = 62.9296 amu; abundance 69.17%) and
65Cu (atomic mass = 64.9278 amu; abundance 30.83%).
Calculate the atomic weight (average atomic mass) of
2.33 (a) In what fundamental way is mass spectrometry related
to Thomson's cathode-ray experiments (Figure 2.4)?
(b) What are the labels on the axes of a mass spectrum?
(c) To measure the mass spectrum of an atom, the atom
must first lose one or more electrons. Why is this so?
2.35 Naturally occurring magnesium has the following isotopic
Isotope Abundance Atomic mass (amu)
(a) What is the average atomic mass of Mg? (b) Sketch
the mass spectrum of Mg.
2.37 For each of the following elements, write its chemical
symbol, locate it in the periodic table, and indicate
whether it is a metal, metalloid, or nonmetal: (a) chromium,
(b) helium, (c) phosphorus, (d) zinc, (e) magnesium,
(f) bromine, (g) arsenic.
2.39 For each of the following elements, write its chemical
symbol, determine the name of the group to which it belongs
(Table 2.3), and indicate whether it is a metal,
metalloid, or nonmetal: (a) potassium, (b) iodine,
(c) magnesium, (d) argon, (e) sulfur.
2.41 What can we tell about a compound when we know the
empirical formula? What additional information is conveyed
by the molecular formula? By the structural formula?
Explain in each case.
2.43 Write the empirical formula corresponding to each of
the following molecular formulas: (a) AI2Br6, (b) C8H10,
(c) C4H802, (d) P4010, (e) C6H4Cl2, (f) B3N3H6.
2.45 How many hydrogen atoms are in each of the following:
(a) C2H5OH, (b) Ca(CH3COO)2, (c) (NH4)3P04?
2.47 Write the molecular and structural formulas for the
compounds represented by the following molecular
2.49 Fill in the gaps in the following table:
2.51 Each of the following elements is capable of forming an
ion in chemical reactions. By referring to the periodic
table, predict the charge of the most stable ion of each:
(a) Mg, (b) AI, (c) K, (d) S, (e) F.
2.53 Using the periodic table to guide you, predict the chemical
formula and name of the compound formed by the
following elements: (a) Ga and F, (b) Li and H, (c) AI
and I, (d) K and S.
2.55 Predict the chemical formula for the ionic compound
formed by (a) Ca2+and Br-, (b) K+ and co32-, (c) Al3+
and CH3COO-, (d) NH4+ and SO42-, (e) Mg2+ and
2.57 Complete the table by filling in the formula for the ionic
compound formed by each pair of cations and anions, as
shown for the first pair.
2.59 Predict whether each of the following compounds is
molecular or ionic: (a) B2H6, (b) CH30H, (c) LiN03,
(d) Sc203, (e) CsBr, (f) NOCl. (g) NF3, (h) Ag2S04.
2.61 Give the chemical formula for (a) chlorite ion, (b) chloride
ion, (c) chlorate ion, (d) perchlorate ion, (e) hypochlorite
2.63 Give the names and charges of the cation and anion in
each of the following compounds: (a) CaO, (b) Na2S04,
(c) KCl04, (d) Fe(N03)2 (e) Cr(OH)3
2.65 Name the following ionic compounds: (a) MgO,
(b) A!Cl3, (c) Li3P04, (d) Ba(Cl04)2, (e) Cu(N03)2,
(f) Fe(OH)2, (g) Ca(C2H302)2, (h) Cr2(C03)3 (i) K2Cr04,
2.67 Write the chemical formulas for the following compounds:
(a) aluminum hydroxide, (b) potassium sulfate,
(c) copper(!) oxide, (d) zinc nitrate, (e) mercury(II) bromide,
(f) iron(lll) carbonate, (g) sodium hypobromite.
2.69 Give the name or chemical formula, as appropriate, for
each of the following acids: (a) HBr03, (b) HBr,
(c) H3P04, (d) hypochlorous acid, (e) iodic acid, (f) sulfurous
2.71 Give the name or chemical formula, as appropriate, for
each of the following binary molecular substances:
(a) SF6, (b) IF5, (c) Xe03, (d) dinitrogen tetroxide, (e) hydrogen
cyanide, (f) tetraphosphorus hexasulfide.
2.73 Write the chemical formula for each substance mentioned
in the following word descriptions (use the front
inside cover to find the symbols for the elements you
don't know). (a) Zinc carbonate can be heated to form
zinc oxide and carbon dioxide. (b) On treatment with
hydrofluoric acid, silicon dioxide forms silicon tetrafluoride
and water. (c) Sulfur dioxide reacts with water to
form sulfurous acid. (d) The substance phosphorus trihydride,
common! y called phosphine, is a toxic gas.
(e) Perchloric acid reacts with cadmium to form cadmium(
ll) perchlorate. (f) Vanadium(III) bromide is a colored
2.75 (a) What is a hydrocarbon? (b) Butane is the alkane with
a chain of four carbon atoms. Write a structural formula
for this compound, and determine its molecular and
2.77 (a) What is a functional group? (b) What functional
group characterizes an alcohol? (c) With reference to Exercise
2.79 Describe a major contribution to science made by each
of the following scientists: (a) Dalton, (b) Thomson,
(c) Millikan, (d) Rutherford.
2.82 The natural abundance of 3He is 0.000137%. (a) How
many protons, neutrons, and electrons are in an atom of
3He? (b) Based on the sum of the masses of their subatomic
particles, which is expected to be more massive,
an atom of 3He or an atom of 3H (which is also called
tritium)? (c) Based on your answer for part (b), what
would need to be the precision of a mass spectrometer
that is able to differentiate between peaks that are due to
3He + and 3H+?
2.85 The diameter of a rubidium atom is 4.95 A. We will consider
two different ways of placing the atoms on a surface.
In arrangement A, all the atoms are lined up with
one another. Arrangement B is called a close-packed
arrangement because the atoms sit in the "depressions"
formed by the previous row of atoms:
(a) Using arrangement A, how many Rb atoms could be
placed on a square surface that is 1.0 em on a side?
(b) How many Rb atoms could be placed on a square
surface that is 1.0 em on a side, using arrangement B?
(c) By what factor has the number of atoms on the surface
increased in going to arrangement B from arrangement
A? If extended to three dimensions, which
arrangement would lead to a greater density for Rb
2.88 The element oxygen has three naturally occurring isotopes,
with 8, 9, and 10 neutrons in the nucleus, respectively.
(a) Write the full chemical symbols for these three
isotopes. (b) Describe the similarities and differences between
the three kinds of atoms of oxygen.
2.91 Gallium (Ga) consists of two naturally occurring isotopes
with masses of 68.926 and 70.925 amu. (a) How
many protons and neutrons are in the nucleus of each
isotope? Write the complete atomic symbol for each,
showing the atomic number and mass number. (b) The
average atomic mass of Ga is 69.72 amu. Calculate the
abundance of each isotope.
2.94 It is common in mass spectrometry to assume that the
mass of a cation is the same as that of its parent atom.
(a) Using data in Table 2.1, determine the number of significant
figures that must be reported before the difference
in mass of 1H and 1H+ is significant. (b) What
percentage of the mass of an 1H atom does the electron
2.98 Name each of the following oxides. Assuming that the
compounds are ionic, what charge is associated with the
metallic element in each case? (a) NiO, (b) Mn02,
(c) Cr203, (d) Mo03.
2.102 Give the chemical names of each of the following familiar
compounds: (a) NaCI (table salt) , (b) NaHC03 (baking
soda), (c) NaOCl (in many bleaches), (d) NaOH
(caustic soda), (e) (NH4)2C03 (smelling salts), (f) Ca504
(plaster of Paris).
2.104 Many ions and compounds have very similar names,
and there is great potential for confusing them. Write
the correct chemical formulas to distinguish between
(a) calcium sulfide and calcium hydrogen sulfide,
(b) hydrobromic acid and bromic acid, (c) aluminum nitride
and aluminum nitrite, (d) iron(ll) oxide and
iron(lll) oxide, (e) ammonia and ammonium ion,
(f) potassium sulfite and potassium bisulfite, (g) mercurous
chloride and mercuric chloride, (h) chloric acid
and perchloric acid.
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