Chapter 2

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 \(2.7]\)

How does Dalton's atomic theory account for the fact that when \(1.000 \mathrm{~g}\) of water is decomposed into its elements, \(0.111\) g of hydrogen and \(0.889 \mathrm{~g}\) of oxygen are obtained regardless of the source of the water?

Hydrogen sulfide is composed of two elements: hydrogen and sulfur. In an experiment, \(6.500 \mathrm{~g}\) of hydrogen sulfide is fully decomposed into its elements. (a) If \(0.384 \mathrm{~g}\) of hydrogen is obtained in this experiment, how many grams of sulfur must be obtained? (b) What fundamental law does this experiment demonstrate? (c) How is this law explained by Dalton's atomic theory?

A chemist finds that \(30.82 \mathrm{~g}\) of nitrogen will react with \(17.60 \mathrm{~g}, 35.20 \mathrm{~g}\), \(70.40 \mathrm{~g}\), or \(88.00 \mathrm{~g}\) 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 theory?

In a series of experiments, a chemist prepared three different compounds that contain only iodine and fluorine and determined the mass of each element in each compound: \(\begin{array}{ccc} \text { Compound } & \text { Mass of Iodine (g) } & \text { Mass of Fluorine (g) } \\ \hline 1 & 4.75 & 3.56 \\ 2 & 7.64 & 3.43 \\ 3 & 9.41 & 9.86 \end{array}\) (a) Calculate the mass of fluorine per gram of iodine in each compound. (b) How do the numbers in part (a) support the atomic theory?

Summarize the evidence used by J. J. Thomson to argue that cathode rays consist of negatively charged particles.

(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?

Millikan determined the charge on the electron by studying the static charges on oil drops falling in an electric field. A student carried out this experiment using several oil drops for her measurements and calculated the charges on the drops. She obtained the following data:

The radius of an atom of krypton \((\mathrm{Kr})\) is about \(1.9 \AA .\) (a) Express this distance in nanometers (nm) and in picometers (pm). (b) How many krypton atoms would have to be lined up to span \(1.0 \mathrm{~mm} ?(\mathrm{c})\) If the atom is assumed to be a sphere, what is the volume in \(\mathrm{cm}^{3}\) of a single \(\mathrm{Kr}\) atom?

An atom of tin (Sn) has a diameter of about \(2.8 \times 10^{-8} \mathrm{~cm}\). (a) What is the radius of a tin atom in angstroms \((\AA)\) and in meters \((\mathrm{m}) ?\) (b) How many Sn atoms would have to be placed side by side to span a distance of \(6.0 \mu \mathrm{m}\) ? (c) If you assume that the tin atom is a sphere, what is the volume in \(\mathrm{m}^{3}\) of a singleatom?

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?

Determine whether each of the following statements is true or false. If false, correct the statement to make it true: (a) The nucleus has most of the mass and comprises most of the volume of an atom; (b) every atom of a given element has the same number of protons; (c) the number of electrons in an atom equals the number of neutrons in the atom; (d) the protons in the nucleus of the helium atom are held together by a force called the strong nuclear force.

(a) Define atomic number and mass number. (b) Which of these can vary without changing the identity of the element?

(a) Which two of the following are isotopes of the same element: \({ }_{16}^{31} \mathrm{X},{15} \mathrm{X},{ }_{16}^{32} \mathrm{X} ?\) (b) What is the identity of the element whose isotopes you have selected?

How many protons, neutrons, and electrons are in the following atoms: (a) \({ }^{40} \mathrm{Ar}\), (b) \({ }^{65} \mathrm{Zn}\), (c) \({ }^{70} \mathrm{Ga}\), (d) \({ }^{80} \mathrm{Br}\), (e) \(^{184} \mathrm{~W}\), (f) \({ }^{243} \mathrm{Am}\) ?

Each of the following isotopes is used in medicine. Indicate the number of protons and neutrons in each isotope: (a) phosphorus-32, (b) chromium-51, (c) cobalt-60, (d) technetium-99, (e) iodine-131; (f) thallium-201.

Fill in the gaps in the following table, assuming each column represents a neutral atom: $$ \begin{array}{|l|l|l|l|l|l|} \hline \text { Symbol } & { }^{52} \mathrm{Cr} & & & & \\ \hline \text { Protons } & & 25 & & & 82 \\ \hline \text { Neutrons } & & 30 & 64 & & \\ \hline \text { Electrons } & & & 48 & 86 & \\ \hline \text { Mass no. } & & & & 222 & 207 \\ \hline \end{array} $$

Fill in the gaps in the following table, assuming each column represents a neutral atom: $$ \begin{array}{|l|l|c|c|c|c|} \hline \text { Symbol } & { }^{65} \mathrm{Zn} & & & & \\ \hline \text { Protons } & & 44 & & & 92 \\ \hline \text { Neutrons } & & 57 & 49 & & \\ \hline \text { Electrons } & & & 38 & 47 & \\ \hline \text { Mass no. } & & & & 108 & 235 \\ \hline \end{array} $$

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 \(84,(\mathrm{c})\) the isotope of arsenic with mass number 75, (d) the isotope of magnesium that has an equal number of protons and neutrons.

One way in which Earth's evolution as a planet can be understood is by measuring the amounts of certain isotopes in rocks. One quantity recently measured is the ratio of \({ }^{129} \mathrm{Xe}\) to \({ }^{130} \mathrm{Xe}\) in some minerals. In what way do these two isotopes differ from one another? \(\ln\) what respects are they the same?

(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.

(a) What is the mass in amu of a carbon-12 atom? (b) Why is the atomic weight of carbon reported as \(12.011\) in the table of elements and the periodic table in the front inside cover of this text?

Only two isotopes of copper occur naturally, \({ }^{63} \mathrm{Cu}\) (atomic mass \(=62.9296\) amu; abundance \(69.17 \%\) ) and \({ }^{65} \mathrm{Cu}\) (atomic mass \(=64.9278\) amu; abundance \(\left.30.83 \%\right)\). Calculate the atomic weight (average atomic mass) of copper.

Rubidium has two naturally occurring isotopes, rubidium- 85 (atomic mass \(=84.9118\) amu; abundance \(=72.15 \%\) ) and rubidium-87 (atomic mass \(=86.9092\) amu; abundance \(=27.85 \%\) ). Calculate the atomic weight of rubidium.

Naturally occurring magnesium has the following isotopic abundances: $$ \begin{array}{ccc} \text { Isotope } & \text { Abundance } & \text { Atomic mass (amu) } \\ \hline{ }^{24} \mathrm{Mg} & 78.99 \% & 23.98504 \\ { }^{25} \mathrm{Mg} & 10.00 \% & 24.98584 \\ { }^{26} \mathrm{Mg} & 11.01 \% & 25.98259 \end{array} $$ (a) What is the average atomic mass of \(\mathrm{Mg}\) ? (b) Sketch the mass spectrum of \(\mathrm{Mg}\).

Mass spectrometry is more often applied to molecules than to atoms. We will see in Chapter 3 that the molecular weight of a molecule is the sum of the atomic weights of the atoms in the molecule. The mass spectrum of \(\mathrm{H}_{2}\) is taken under conditions that prevent decomposition into \(\mathrm{H}\) atoms. The two naturally occurring isotopes of hydrogen are \({ }^{1} \mathrm{H}\) (atomic mass \(=1.00783\) amu; abundance \(99.9885 \%\) ) and \({ }^{2} \mathrm{H}\) (atomic mass \(=2.01410 \mathrm{amu}\); abundance \(0.0115 \%\). (a) How many peaks will the mass spectrum have? (b) Give the relative atomic masses of each of these peaks. (c) Which peak will be the largest, and which the smallest?

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.

Locate each of the following elements in the periodic table; indicate whether it is a metal, metalloid, or nonmetal; and give the name of the element: (a) \(\mathrm{Ca}\), (b) \(\mathrm{Ti}\), (c) \(\mathrm{Ga},(\mathrm{d}) \mathrm{Th},(\mathrm{e}) \mathrm{Pt},(\mathrm{f}) \mathrm{Se},(\mathrm{g}) \mathrm{Kr}\).

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.

The elements of group 4 A show an interesting change in properties moving down the group. Give the name and chemical symbol of each element in the group, and label it as a nonmetal, metalloid, or metal.

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.

Two compounds have the same empirical formula. One substance is a gas, the other is a viscous liquid. How is it possible for two substances with the same empirical formula to have markedly different properties?

Write the empirical formula corresponding to each of the following molecular formulas: (a) \(\mathrm{Al}_{2} \mathrm{Br}_{6}\), (b) \(\mathrm{C}_{8} \mathrm{H}_{10}\), (c) \(\mathrm{C}_{4} \mathrm{H}_{8} \mathrm{O}_{2}\), (d) \(\mathrm{P}_{4} \mathrm{O}_{10}\) (e) \(\mathrm{C}_{6} \mathrm{H}_{4} \mathrm{Cl}_{2}\) (f) \(\mathrm{B}_{3} \mathrm{~N}_{3} \mathrm{H}_{6}\).

Determine the molecular and empirical formulas of the following: (a) The organic solvent benzene, which has six carbon atoms and six hydrogen atoms; (b) the compound silicon tetrachloride, which has a silicon atom and four chlorine atoms and is used in the manufacture of computer chips; (c) the reactive substance diborane, which has two boron atoms and six hydrogen atoms; (d) the sugar called glucose, which has six carbon atoms, twelve hydrogen atoms, and six oxygen atoms.

How many hydrogen atoms are in each of the following: (a) \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}\), (b) \(\mathrm{Ca}\left(\mathrm{CH}_{3} \mathrm{COO}\right)_{2}\) (c) \(\left(\mathrm{NH}_{4}\right)_{3} \mathrm{PO}_{4} ?\)

How many of the indicated atoms are represented by each chemical formula: (a) carbon atoms in \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{COOCH}_{3}\), (b) oxygen atoms in \(\mathrm{Ca}\left(\mathrm{ClO}_{4}\right)_{2},(\mathrm{c}) \mathrm{hy}-\) drogen atoms in \(\left(\mathrm{NH}_{4}\right)_{2} \mathrm{HPO}_{4} ?\)

Fill in the gaps in the following table: $$ \begin{array}{|l|l|c|c|c|} \hline \text { Symbol } & { }^{59} \mathrm{Co}^{3+} & & & \\ \hline \text { Protons } & & 34 & 76 & 80 \\ \hline \text { Neutrons } & & 46 & 116 & 120 \\ \hline \text { Electrons } & & 36 & & 78 \\ \hline \text { Net charge } & & & 2+ & \\ \hline \end{array} $$

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) \(\mathrm{Mg}\), (b) \(\mathrm{AI},(\mathrm{c}) \mathrm{K},(\mathrm{d}) \mathrm{S},(\mathrm{e}) \mathrm{F}\)

Using the periodic table, predict the charges of the ions of the following elements: (a) \(\mathrm{Ga}\), (b) \(\mathrm{Sr}\), (c) As, (d) Br, (e) Se.

Using the periodic table to guide you, predict the chemical formula and name of the compound formed by the following elements: (a) Ga and \(\mathrm{F}\), (b) \(\mathrm{Li}\) and \(\mathrm{H}\), (c) Al and \(\mathrm{I}\), (d) \(\mathrm{K}\) and \(\mathrm{S}\).

The most common charge associated with silver in its compounds is \(1+\). Indicate the chemical formulas you would expect for compounds formed between \(\mathrm{Ag}\) and (a) iodine, (b) sulfur, (c) fluorine.

Predict the chemical formula for the ionic compound formed by (a) \(\mathrm{Ca}^{2+}\) and \(\mathrm{Br}^{-}\), (b) \(\mathrm{K}^{+}\) and \(\mathrm{CO}_{3}^{2-}\), (c) \(\mathrm{Al}^{3+}\) and \(\mathrm{CH}_{3} \mathrm{COO}^{-}\), (d) \(\mathrm{NH}_{4}{\underline{\phantom{xx}}}^{+}\) and \(\mathrm{SO}_{4}{\underline{\phantom{xx}}}^{2-}\), (e) \(\mathrm{Mg}^{2+}\) and \(\mathrm{PO}_{4}^{3-}\)

Predict the chemical formulas of the compounds formed by the following pairs of ions: (a) \(\mathrm{Cu}^{2+}\) and \(\mathrm{Br}^{-}\), (b) \(\mathrm{Fe}^{3+}\) and \(\mathrm{O}^{2-}\), (c) \(\mathrm{Hg}_{2}^{2+}\) and \(\mathrm{CO}_{3}^{2-}\), (d) \(\mathrm{Ca}^{2+}\) and \(\mathrm{AsO}_{4}{\underline{\phantom{xx}}}^{3-}\), (e) \(\mathrm{NH}_{4}{\underline{\phantom{xx}}}^{+}\) and \(\mathrm{CO}_{3}{\underline{\phantom{xx}}}^{2-}\).

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. $$ \begin{array}{|l|c|c|c|c|} \hline \text { Ion } & \mathrm{K}^{+} & \mathrm{NH}_{4}{\underline{\phantom{xx}}}^{+} & \mathrm{Mg}^{2+} & \mathrm{Fe}^{3+} \\ \hline \mathrm{Cl}^{-} & \mathrm{KCl} & & & \\ \hline \mathrm{OH}^{-} & & & & \\ \hline \mathrm{CO}_{3}^{2-} & & & & \\ \hline \mathrm{PO}_{4}{\underline{\phantom{xx}}}^{3-} & & & & \\ \hline \end{array} $$

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. $$ \begin{array}{|l|c|c|c|c|} \hline \text { lon } & \mathrm{Na}^{+} & \mathrm{Ca}^{2+} & \mathrm{Fe}^{2+} & \mathrm{Al}^{3+} \\ \hline \mathrm{O}^{2-} & \mathrm{Na}_{2} \mathrm{O} & & & \\ \hline \mathrm{NO}_{3}^{-} & & & & \\ \hline \mathrm{SO}_{4}^{2-} & & & & \\ \hline \mathrm{AsO}_{4}^{3-} & & & & \\ \hline \end{array} $$

Predict whether each of the following compounds is molecular or ionic: (a) \(\mathrm{B}_{2} \mathrm{H}_{6}\), (b) \(\mathrm{CH}_{3} \mathrm{OH}\), (c) \(\mathrm{LiNO}_{3}\) (d) \(\mathrm{Sc}_{2} \mathrm{O}_{3},(\mathrm{e}) \mathrm{CsBr}\), (f) \(\mathrm{NOCl}\), \((\mathrm{g}) \mathrm{NF}_{3}\), (h) \(\mathrm{Ag}_{2} \mathrm{SO}_{4}\).

Which of the following are ionic, and which are molecular? (a) \(\mathrm{PF}_{5}\), (b) \(\mathrm{NaI}\), (c) \(\mathrm{SCl}_{2}\), (d) \(\mathrm{Ca}\left(\mathrm{NO}_{3}\right)_{2}\), (e) \(\mathrm{FeCl}_{3}\) (f) \(\mathrm{LaP},(\mathrm{g}) \mathrm{CoCO}_{3},(\mathrm{~h}) \mathrm{N}_{2} \mathrm{O}_{4}\).

Give the chemical formula for (a) chlorite ion, (b) chloride ion, (c) chlorate ion, (d) perchlorate ion, (e) hypochlorite ion.

Selenium, an element required nutritionally in trace quantities, forms compounds analogous to sulfur. Name the following ions: (a) \(\mathrm{SeO}_{4}{\underline{\phantom{xx}}}^{2-}\), (b) \(\mathrm{Se}^{2-}\), (c) HSe, (d) \(\mathrm{HSeO}_{3}^{-}\).

Give the names and charges of the cation and anion in each of the following compounds: (a) \(\mathrm{CaO}\), (b) \(\mathrm{Na}_{2} \mathrm{SO}_{4}\) (c) \(\mathrm{KClO}_{4},(\mathrm{~d}) \mathrm{Fe}\left(\mathrm{NO}_{3}\right)_{2},(\mathrm{e}) \mathrm{Cr}(\mathrm{OH})_{3}\)