Chapter 2

Atoms: Their Composition and Structure What are the three fundamental particles from which atoms are built? What are their electric charges? Which of these particles constitute the nucleus of an atom? Which is the least massive particle of the three?

Around 1910 Rutherford carried out his now-famous alpha-particle scattering experiment. What surprising observation did he make in this experiment and what conclusion did he draw from it?

What scientific instrument was used to discover that not all atoms of neon have the same mass?

If a gold atom has a radius of \(145 \mathrm{pm},\) and you could string gold atoms like beads on a thread, how many atoms would you need to have a necklace \(36 \mathrm{cm}\) long?

The volcanic eruption of Mount St. Helens in the state of Washington in 1980 produced a considerable quantity of a radioactive element in the gaseous state. The element has atomic number \(86 .\) What are the symbol and name of this element?

Titanium and thallium have symbols that are easily confused with each other. Give the symbol, atomic number, atomic weight, and group and period number of each element. Are they metals, metalloids, or nonmetals?

Give the mass number of each of the following atoms: (a) magnesium with 15 neutrons, (b) titanium with 26 neutrons, and (c) zinc with 32 neutrons.

Give the mass number of (a) a nickel atom with 31 neutrons, (b) a plutonium atom with 150 neutrons, and (c) a tungsten atom with 110 neutrons.

Give the complete symbol \(\left(\frac{4}{z} \mathrm{X}\right)\) for each of the following atoms: (a) potassium with 20 neutrons, (b) krypton with 48 neutrons, and (c) cobalt with 33 neutrons.

Give the complete symbol \(\left(\frac{A}{Z} X\right)\) for each of the following atoms: (a) fluorine with 10 neutrons, (b) chromium with 28 neutrons, and (c) xenon with 78 neutrons.

How many electrons, protons, and neutrons are there in an atom of (a) magnesium- \(24,^{24} \mathrm{Mg} ;\) (b) tin- \(119,^{119} \mathrm{Sn}\) and (c) thorium-232, \(^{232}\) Th?

How many electrons, protons, and neutrons are there in an atom of (a) carbon-13, \(^{13} \mathbf{C} ;\) (b) copper-63, \(^{\mathbf{6 3}} \mathbf{C u} ;\) and (c) bismuth- \(205,^{205} \mathrm{Bi} ?\)

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

Radioactive americium-241 is used in household smoke detectors and in bone mineral analysis. Give the number of electrons, protons, and neutrons in an atom of americium-241.

Cobalt has three radioactive isotopes used in medical studies. Atoms of these isotopes have \(30,31,\) and 33 neutrons, respectively. Give the symbol for each of these isotopes.

Which of the following are isotopes of element X, the atomic number for which is \(9:^{19} \mathrm{X},^{20} \mathrm{X}, 18 \mathrm{X},\) and \(^{21} \mathrm{X} ?\)

Isotope Abundance and Atomic Mass Thallium has two stable isotopes, \(^{203} \mathrm{Tl}\) and \(^{205} \mathrm{T}\). Knowing that the atomic weight of thallium is \(204.4,\) which isotope is the more abundant of the two?

Strontium has four stable isotopes. Strontium-84 has a very low natural abundance, but \(^{86} \mathrm{Sr},^{87} \mathrm{Sr},\) and \(^{88} \mathrm{Sr}\) are all reasonably abundant. Knowing that the atomic weight of strontium is \(87.62,\) which of the more abundant isotopes predominates?

Verify that the atomic mass of lithium is \(6.94,\) given the following information: \(^{6} \mathrm{Li},\) mass \(=6.015121 \mathrm{u} ;\) percent abundance \(=7.50 \%\) \(^{7} \mathrm{Li},\) mass \(=7.016003 \mathrm{u} ;\) percent abundance \(=92.50 \%\)

Calculate the mass, in grams, of (a) 4.24 mol of gold (b) 15.6 mol of \(\mathrm{He}\) (c) 0.063 mol of platinum (d) \(3.63 \times 10^{-4}\) mol of \(\mathrm{Pu}\)

Calculate the amount (moles) represented by each of the following: (a) \(127.08 \mathrm{g}\) of \(\mathrm{Cu}\) (b) 0.012 g of lithium (c) 5.0 mg of americium (d) \(6.75 \mathrm{g}\) of \(\mathrm{Al}\)

Calculate the amount (moles) represented by each of the following: (a) \(16.0 \mathrm{g}\) of \(\mathrm{Na}\) (b) 0.876 g of tin (c) \(0.0034 \mathrm{g}\) of platinum (d) \(0.983 \mathrm{g}\) of \(\mathrm{Xe}\)

You are given 1.0 -g samples of He, Fe, \(\mathrm{I}\) i, \(\mathrm{Si}\), and \(\mathrm{C}\). Which sample contains the largest number of atoms? Which contains the smallest?

You are given 1.0 -mol amounts of \(\mathrm{He}, \mathrm{Fe}, \mathrm{Li}, \mathrm{Si},\) and \(\mathrm{C}\) Which sample has the largest mass?

The Periodic Table Give the name and symbol of each of the Group 5 A elements. Tell whether each is a metal, nonmetal, or metalloid.

How many periods of the periodic table have 8 elements, how many have 18 elements, and how many have 32 elements?

How many elements occur in the seventh period? What is the name given to the majority of these elements and what well-known property characterizes them?

Give the name and chemical symbol for the following. (a) a nonmetal in the second period (b) an alkali metal (c) the third-period halogen (d) an element that is a gas at \(20^{\circ} \mathrm{C}\) and 1 atmosphere pressure

Classify the following elements as metals, metalloids, or nonmetals: \(\mathrm{N}, \mathrm{Na}, \mathrm{Ni}, \mathrm{Ne},\) and \(\mathrm{Np}.\)

Here are symbols for five of the seven elements whose names begin with the letter \(\mathrm{B}:\) B, \(\mathrm{Ba}\), \(\mathrm{Bk}\), \(\mathrm{Bi}\), and \(\mathrm{Br}\). Match each symbol with one of the descriptions below. (a) a radioactive element (b) a liquid at room temperature (c) a metalloid (d) an alkaline earth element (e) a Group 5 A element

Use the elements in the following list to answer the questions: sodium, silicon, sulfur, scandium, selenium, strontium, silver, and samarium. (Some elements will be entered in more than one category.) (a) Identify those that are metals. (b) Identify those that are main group elements (c) Identify those that are transition metals.

Compare the elements silicon (Si) and phosphorus (P) using the following criteria: (a) metal, metalloid, or nonmetal (b) possible conductor of electricity (c) physical state at \(25^{\circ} \mathrm{C}\) (solid, liquid, or gas)

Fill in the blanks in the table (one column per element). Symbol \(\quad$$58 \mathrm{Ni}$$\quad$$^{86} \mathrm{Kr}$$\quad\)____\(\quad\)____ Number of protons _____ \(\quad\)_____\(\quad\) 78 \(\quad\)____ Number of neutrons _____ \(\quad\)_____\(\quad\) 117\(\quad\)46 Number of electrons in the neutral atom _____ \(\quad\)_____\(\quad\)_____\(\quad\)35 Name of element_____ \(\quad\)_____\(\quad\)_____\(\quad\)____

Crossword Puzele: In the \(2 \times 2\) box shown here, each answer must be correct four ways: horizontally, vertically, diagonally, and by itself. Instead of words, use symbols of elements. When the puzzle is complete, the four spaces will contain the overlapping symbols of ten elements. There is only one correct solution. $$\begin{array}{|l|l|} \hline 1 & 2 \\ \hline 3 & 4 \\ \hline \end{array}$$ Horizontal 1-2: Two-letter symbol for a metal used in ancient times 3-4: Two- letter symbol for a metal that burns in air and is found in Group \(5 \mathrm{A}\) Vertical 1-3: Two-letter symbol for a metalloid 2-4: Two-letter symbol for a metal used in U.S. coins single squares: all one-letter symbols 1: A colorful nonmetal 2: Colorless gaseous nonmetal 3: An element that makes fireworks green 4: 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 This puzzle first appeared in Chemical \(\mathscr{E}\) Engineering News, p. \(86,\) December 14,1987 (submitted by S. J. Cyvin) and in Chem Matters, October 1988.

The molecule buckminsterfullerene, commonly called a "buckyball," is one of three common allotropes of a familiar element. Identify two other allotropes of this element.

Give the symbol for a metalloid in the third period and then identify a property of this element.

Reviewing the periodic table. (a) Name an element in Group 2 A. (b) Name an element in the third period. (c) Which element is in the second period in Group \(4 \mathrm{A} ?\) (d) Which element is in the third period in Group \(6 \mathrm{A} ?\) (e) Which halogen is in the fifth period? (f) Which alkaline earth element is in the third period? (g) Which noble gas element is in the fourth period? (h) Name the nonmetal in Group 6A and the third period. (i) Name a metalloid in the fourth period.

Reviewing the periodic table: (a) Name an element in Group 2 B. (b) Name an element in the fifth period. (c) Which element is in the sixth period in Group \(4 \mathrm{A} ?\) (d) Which element is in the third period in Group \(6 \mathrm{A} ?\) (e) Which alkali metal is in the third period? (f) Which noble gas element is in the fifth period? (g) Name the element in Group \(6 A\) and the fourth period. Is it a metal, nonmetal, or metalloid? (h) Name a metalloid in Group \(5 \mathrm{A}\).

Give two examples of nonmetallic elements that have allotropes. Name those elements and describe the allotropes of each.

In each case, decide which represents more mass: (a) 0.5 mol of \(\mathrm{Na}\) or 0.5 mol of \(\mathrm{Si}\) (b) \(9.0 \mathrm{g}\) of \(\mathrm{Na}\) or 0.50 mol of \(\mathrm{Na}\) (c) 10 atoms of \(\mathrm{Fe}\) or 10 atoms of \(\mathrm{K}\)

A semiconducting material is composed of \(52 \mathrm{g}\) of \(\mathrm{Ga}\), \(9.5 \mathrm{g}\) of \(\mathrm{Al}\), and \(112 \mathrm{g}\) of As. Which element has the largest number of atoms in the final mixture?

You are given \(15 \mathrm{g}\) each of yterium, boron, and copper. Which sample represents the largest number of atoms?

Superman comes from the planet Krypton. If you have \(0.00789 \mathrm{g}\) of the gaseous element krypton, how many moles does this represent? How many atoms?

The recommended daily allowance (RDA) of iron in your diet is 15 mg. How many moles is this? How many atoms?

Put the following elements in order from smallest to largest mass: (a) \(3.79 \times 10^{24}\) atoms Fe (e) 9.221 mol \(\mathrm{Na}\) (b) \(19.921 \mathrm{mol} \mathrm{H}_{2}\) (f) \(4.07 \times 10^{24}\) atoms Al (c) 8.576 mol \(C\) (g) 9.2 mol \(\mathrm{Cl}_{2}\) (d) \(7.4 \mathrm{mol} \mathrm{Si}\)

When a sample of phosphorus burns in air, the compound \(P_{4} O_{10}\) forms. One experiment showed that \(0.744 \mathrm{g}\) of phosphorus formed \(1.704 \mathrm{g}\) of \(\mathrm{P}_{4} \mathrm{O}_{10} .\) Use this information to determine the ratio of the atomic masses of phosphorus and oxygen (mass \(\mathrm{P} / \mathrm{mass}\) O). If the atomic mass of oxygen is assumed to be 16.000 u, calculate the atomic mass of phosphorus.

The data below were collected in a Millikan oil drop experiment. $$\begin{array}{ll} \hline \text { Oil Drop } & \text { Measured Charge on Drop (C) } \\ \hline 1 & 1.59 \times 10^{-19} \\ 2 & 11.1 \times 10^{-19} \\ 3 & 9.54 \times 10^{-19} \\ 4 & 15.9 \times 10^{-19} \\ 5 & 6.36 \times 10^{-19} \\ \hline \end{array}$$ (a) Use these data to calculate the charge on the electron (in coulombs). (b) How many electrons have accumulated on each oil drop? (c) The accepted value of the electron charge is \(1.60 \times\) \(10^{-19} \mathrm{C} .\) Calculate the percent and error for the value determined by the data in the table.

A Although carbon-12 is now used as the standard for atomic masses, this has not always been the case. Farly attempts at classification used hydrogen as the standard, with the mass of hydrogen being set equal to 1.0000 u. Later attempts defined atomic masses using oxygen (with a mass of \(16.0000 \mathrm{u}\) ). In each instance, the atomic masses of the other elements were defined relative to these masses. (To answer this question, you need more precise data on current atomic masses: \(\mathrm{H}, 1.00794 \mathrm{u} ; \mathrm{O}\) \(15.9994 \mathrm{u} .)\) (a) If \(\mathrm{H}=1.0000 \mathrm{u}\) was used as a standard for atomic masses, what would the atomic mass of oxygen be? What would be the value of Avogadro's number under these circumstances? (b) Assuming the standard is \(\mathrm{O}=16.0000 \mathrm{u}\), determine the value for the atomic mass of hydrogen and the value of Avogadro's number.

A reagent occasionally used in chemical synthesis is sodium-potassium alloy. (Alloys are mixtures of metals, and Na-K has the interesting property that it is a liquid.) One formulation of the alloy (the one that melts at the lowest temperature) contains 68 atom percent \(\mathbf{K} ;\) that is, out of every 100 atoms, 68 are \(\mathrm{K}\) and 32 are \(\mathrm{Na}\). What is the weight percent of potassium in sodium-potassium alloy?

Mass spectrometric analysis showed that there are four isotopes of an unknown element having the following masses and abundances: $$\begin{array}{llll} \hline \text { Isotope } & \text { Mass } \text { Number } & \text { Isotope Mass } & \text { Abundance }(\%) \\ \hline 1 & 136 & 135.9090 & 0.193 \\ 2 & 138 & 137.9057 & 0.250 \\ 3 & 140 & 139.9053 & 88.48 \\ 4 & 142 & 141.9090 & 11.07 \\ \hline \end{array}$$ Three elements in the periodic table that have atomic weights near these values are lanthanum (La), atomic number 57 , atomic weight \(139.9055 ;\) cerium (Ce), atomic number \(58,\) atomic weight \(140.115 ;\) and praeseodymium (Pr), atomic number 59 , atomic weight \(140.9076 .\) Using the data above, calculate the atomic weight and identify the element if possible.