Chapter 2

Identify the fundamental unit of electrical charge.

In any given neutral atom, how many protons are there compared with the number of electrons?

Atoms of elements can have varying numbers of neutrons in their nuclei. (a) What are species called that have varying numbers of neutrons for the same element? (b) How do the mass numbers vary for these species? (c) What are two common elements that exemplify this property?

Define these terms: (a) unified atomic mass unit; (b) mass number; (c) molar mass; (d) isotope.

A dictionary defines the word "compound" as a "combination of two or more parts." What are the "parts" of a chemical compound? Identify three pure (or nearly pure) compounds you have encountered today. What is the difference between a compound and a mixture?

If the nucleus of an atom were the size of a golf ball (4-cm diameter), what would be the diameter of the atom?

If the nucleus of an atom were the size of Earth, would the moon be within the atom? Would the sun be within the atom? (Use the Internet to find information about the distances from Earth to the moon and sun.)

Match these by placing the correct notation in the appropriate blank. \(\begin{array}{lll}{\underline{\phantom{xx}}}_{34}^{67} \mathrm{Se} & { }_{33}^{67} \mathrm{As} & { }_{35}^{67} \mathrm{Br} & { }_{36}^{72} \mathrm{Kr}\end{array}\) ____a. Contains 33 neutrons ____b. Contains greatest number of neutrons ____c. Contains equal number of protons and neutrons ____d. Contains the same number of neutrons as there are protons in As-67

Both scanning tunneling microscopy and mass spectrometry use electrons to help measure different properties of atoms and molecules. Describe the role that electrons play in each technique.

What is plotted on the \(x\) -axis and on the \(y\) -axis in a mass spectrum? What information does a mass spectrum convey?

Bromine has two isotopes, bromine- \(79(50.69 \%\) abundance) and bromine- \(81(49.31 \%\) abundance). Draw a graph of the mass spectrum obtained when a sample of \(\mathrm{Br}_{2}\) gas is run through a mass spectrometer.

Chlorine consists of two isotopes, chlorine- \(35(75.77 \%\) abundance) and chlorine- 37 ( \(24.23 \%\) abundance). Draw a graph of the mass spectrum obtained from a sample of \(\mathrm{Cl}_{2}\) gas.

Uranium-235 and uranium- 238 differ in terms of the number of subatomic particles. For which subatomic particle is the number different and by how much?

Strontium- 90 is a product formed when atomic bombs exploded. How do strontium-90 and strontium- 88 differ in terms of the number of subatomic particles?

How many electrons, protons, and neutrons are present in an atom of cobalt-60?

The artificial radioactive element technetium is used in many medical studies. Give the number of electrons, protons, and neutrons in an atom of technetium-99.

The atomic weight of bromine is 79.904 . The natural abundance of \({ }^{81} \mathrm{Br}\), atomic weight \(80.916289 \mathrm{u}\), is \(49.31 \%\). What is the atomic weight of the only other natural isotope of bromine?

The atomic weight of boron is 10.811 . The natural abundance of \({ }^{10} \mathrm{~B}\) is \(19.91 \%\). Determine the atomic weight of the only other natural isotope of boron.

Give the complete symbol \({ }_{Z}^{A} \mathrm{X}\) for each of these atoms: (a) sodium with 12 neutrons, (b) argon with 21 neutrons, and (c) gallium with 38 neutrons.

Give the complete symbol \({ }_{Z}^{A} \mathrm{X}\) for each of these atoms: (a) nitrogen with 8 neutrons, (b) zinc with 34 neutrons, and (c) xenon with 75 neutrons.

Verify that the average atomic mass of lithium is 6.941 , given this information: \({ }^{6} \mathrm{Li},\) exact mass \(=6.015121 \mathrm{u}\) percent abundance \(=7.500 \%\) \({ }^{7} \mathrm{Li},\) exact mass \(=7.016003 \mathrm{u}\) percent abundance \(=92.50 \%\)

Verify that the average atomic mass of magnesium is 24.3050 , given this information: \({ }^{24} \mathrm{Mg},\) exact mass \(=23.985042 \mathrm{u}\) \({ }^{25} \mathrm{Mg},\) exact mass \(=24.985837 \mathrm{u}\) percent abundance \(=10.00 \%\) \({ }^{26} \mathrm{Mg}\), exact mass \(=25.982593 \mathrm{u}\) percent abundance \(=11.01 \%\)

Argon has three naturally occurring isotopes: \(0.3336 \%\) \({ }^{36} \mathrm{Ar}, 0.063 \%{ }^{38} \mathrm{Ar}\), and \(99.60 \%{ }^{40} \mathrm{Ar}\). Estimate the average atomic mass of argon. If the masses of the isotopes are \(35.968 \mathrm{u}, 37.963 \mathrm{u},\) and \(39.962 \mathrm{u},\) respectively, calculate the average atomic mass of natural argon.

For each of these metals, write the chemical symbol for the corresponding monoatomic ion (with charge). (a) Lithium (b) Strontium (c) Aluminum (d) Zinc

For each of these nonmetals, write the chemical symbol for the corresponding monoatomic ion (with charge). (a) Nitrogen (b) Sulfur (c) Chlorine (d) Iodine

Predict the charges for monoatomic ions of these elements. (a) Magnesium (b) Phosphorus (c) Iron (d) Selenium

Predict the charges for monoatomic ions of these elements. (a) Gallium (b) Fluorine (c) Silver (d) Nitrogen

Cobalt is a transition metal and thus can form ions with at least two different charges. Write the formulas for the compounds formed between cobalt ions and the oxide ion.

Although not a transition element, lead can form two cations: \(\mathrm{Pb}^{2+}\) and \(\mathrm{Pb}^{4+}\). Write the formulas for the compounds of these ions with the chloride ion.

Which of these are the correct formulas of compounds? For those that are not, give the correct formula. (a) \(\mathrm{AlCl}\) (b) \(\mathrm{NaF}_{2}\) (c) \(\mathrm{Ga}_{2} \mathrm{O}_{3}\) (d) \(\mathrm{MgS}\)

Which of these are the correct formulas of compounds? For those that are not, give the correct formula. (a) \(\mathrm{Ca}_{2} \mathrm{O}\) (b) \(\mathrm{SrCl}_{2}\) (c) \(\mathrm{Fe}_{2} \mathrm{O}_{5}\) (d) \(\mathrm{K}_{2} \mathrm{O}\)

Predict which compounds are ionic. Explain your answers. (a) \(\mathrm{CF}_{4}\) (b) \(\mathrm{SrBr}_{2}\) (c) \(\mathrm{Co}\left(\mathrm{NO}_{3}\right)_{3}\) (d) \(\mathrm{SiO}_{2}\) (e) \(\mathrm{KCN}\) (f) \(\mathrm{SCl}_{2}\)

Predict which compounds are ionic. Explain your answers. (a) \(\mathrm{NaH}\) (b) \(\mathrm{HCl}\) (c) \(\mathrm{NH}_{3}\) (d) \(\mathrm{CH}_{4}\) (e) HI

Determine the chemical formulas for barium sulfate, magnesium nitrate, and sodium acetate. Each compound contains a monoatomic cation and a polyatomic anion. What are the names and electrical charges of these ions?

Write the chemical formula for calcium nitrate, barium chloride, and ammonium phosphate. What are the names and charges of all the ions in these three compounds?

Write the chemical formulas for these compounds. (a) Nickel(II) nitrate (b) Sodium bicarbonate (c) Lithium hypochlorite (d) Magnesium chlorate (e) Calcium sulfite

Write the chemical formulas for these compounds. (a) Iron(III) nitrate (b) Potassium carbonate (c) Sodium phosphate (d) Calcium chlorite (e) Sodium sulfate

Give the correct formula for each of these ionic compounds. (a) Ammonium carbonate (b) Calcium iodide (c) Copper(II) bromide (d) Aluminum phosphate

Give the correct formula for each of these ionic compounds. (a) Calcium hydrogen carbonate (b) Potassium permanganate (c) Magnesium perchlorate (d) Ammonium monohydrogen phosphate

Correctly name each of these ionic compounds. (a) \(\mathrm{K}_{2} \mathrm{~S}\) (b) \(\mathrm{NiSO}_{4}\) (c) \(\left(\mathrm{NH}_{4}\right)_{3} \mathrm{PO}_{4}\) (d) \(\mathrm{Al}(\mathrm{OH})_{3}\) (e) \(\mathrm{Co}_{2}\left(\mathrm{SO}_{4}\right)_{3}\)

Correctly name each of these ionic compounds. (a) \(\mathrm{KH}_{2} \mathrm{PO}_{4}\) (b) \(\mathrm{CuSO}_{4}\) (c) \(\mathrm{CrCl}_{3}\) (d) \(\mathrm{Ca}\left(\mathrm{CH}_{3} \mathrm{COO}\right)_{2}\) (e) \(\mathrm{Fe}_{2}\left(\mathrm{SO}_{4}\right)_{3}\)

Solid magnesium oxide melts at \(2800^{\circ} \mathrm{C}\). This property, combined with the fact that magnesium oxide is not an electrical conductor, makes it an ideal heat insulator for electric wires in cooking ovens and toasters. In contrast, solid \(\mathrm{NaCl}\) melts at the relatively low temperature of \(801{ }^{\circ} \mathrm{C}\). What is the formula of magnesium oxide? Suggest a reason that it has a melting temperature so much higher than that of \(\mathrm{NaCl}\).

Assume you have an unlabeled bottle containing a white, crystalline powder. The powder melts at \(310^{\circ} \mathrm{C}\). You are told that it could be \(\mathrm{NH}_{3}, \mathrm{NO}_{2}\), or \(\mathrm{NaNO}_{3}\). What do you think it is and why?

Identify each compound as ionic or molecular based on its formula or properties. (a) \(\mathrm{Rb}_{2} \mathrm{O}\) (b) \(\mathrm{C}_{6} \mathrm{H}_{12}\) (c) Liquid at room temperature (d) Conducts electricity when molten

Identify each compound as ionic or molecular based on its formula or properties. (a) Can be cleaved with a sharp wedge (b) Melts at \(-22.3^{\circ} \mathrm{C}\) (c) \(\mathrm{MgBr}_{2}\) (d) \(\mathrm{C}_{5} \mathrm{H}_{10} \mathrm{O}_{2} \mathrm{~N}\)

Given these condensed formulas, write the structural and molecular formulas. (a) \(\mathrm{CH}_{3} \mathrm{OH}\) (b) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{NH}_{2}\) (c) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{SCH}_{2} \mathrm{CH}_{3}\) (d) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{SH}\)

Write molecular and structural formulas for these compounds. (a) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{NHCH}_{2} \mathrm{CH}_{3}\) (b) \(\mathrm{CH}_{3} \mathrm{NH}_{2}\) (c) \(\mathrm{CH}_{3} \mathrm{CHClCH}_{3}\) (d) \(\mathrm{CH}_{2} \mathrm{OHCHOHCH}_{2} \mathrm{OH}\)

Write the molecular formula for each substance. (a) The hydrocarbon heptane, which has seven carbon atoms and 16 hydrogen atoms (b) Acrylonitrile (the basis of Orlon and Acrilan fibers), which has three carbon atoms, three hydrogen atoms, and one nitrogen atom

Write the molecular formula for each substance. (a) Fenclorac, an anti-inflammatory drug, which has 14 carbon atoms, 16 hydrogen atoms, two chlorine atoms, and two oxygen atoms. (b) Vitamin B-12, which has 63 carbon atoms, 88 hydrogen atoms, one cobalt atom, 14 nitrogen atoms, 14 oxygen atoms, and one phosphorus atom.

Give the total number of atoms of each element in one formula unit of each of these compounds. (a) \(\mathrm{CaC}_{2} \mathrm{O}_{4}\) (b) \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{CHCH}_{2}\) (c) \(\left(\mathrm{NH}_{4}\right)_{2} \mathrm{SO}_{4}\) (d) \(\mathrm{Pt}\left(\mathrm{NH}_{3}\right)_{2} \mathrm{Cl}_{2}\) (e) \(\mathrm{K}_{4} \mathrm{Fe}(\mathrm{CN})_{6}\)