Chapter 2.4 Periodic properties of the elements Configurations, Atomic Properties, and As we move down the the electron configuration becomes longer and more complex. This goes beyond the purpose of our course.

Electron configurations help to determine the atomic and chemical properties of the elements. Properties such as atomic radius, ionization , electron affinity and are periodic as they follow recurring trends in the periodic table. increase the orbital energy in oxygen. Therefore, less energy is required to remove the fourth p sublevel electron in oxygen. Periodic trends in are linked to trends involving the reactivity of . In general, the chemical reactivity of metals increases down a and decreases across a . These trends, as well as a further trend from metallic to non-metallic properties across a period, and increasing metallic properties down a group, are shown in Table 3.1. Table 3.1 Periodic Trends in Reactivity of Metals With oxygen Reaction with Reaction in the air With water dilute acids Group 1 React rapidly to form React vigorously The reaction is oxides with the with cold water, dangerously general formula M2O. generating H2(g) violent, igniting These compounds and forming a H2(g) generated. are strong bases. strong base with the general formula MOH. Group 2 React moderately to React slowly in React quickly form basic oxides cold water, generating H2(g). with the general generating H2(g) Electron Configurations,formula MO. Atomicand forming a Properties, and strong base, Periodic Trends M(OH)2.

Group 13 React slowly. Al displaces H2(g) Al reacts readily PeriodicAluminum Trends forms an in Reactivityfrom steam. of Metalsif the protective Reaction Withoxide oxygen coating in thatthe air Withoxide water coating is Reaction with dilute protects the ; removed, to acids Group 1 React rapidlythe to compoundform oxides Al with2O3 the React vigorouslygenerate with cold H 2(g)water, . The reaction is dangerously can act as a base or general formula M2O. These compounds generating H2(g) and forming a violent, igniting H2(g) are strong bases.an acid. strong base with the general generated. Group 14 C and Si are non- The mostformula metallic MOH. Sn and Pb react Group 2 React moderatelymetals, to and form form basic oxideselements, React Sn slowly and in coldslowly water, to form React quickly generating with the generalacidic formula oxides. MO. Ge Pb, dogenerating not react H2(g)H and2(g) .forming a H2(g). is a , and with water. strong base, M(OH)2. forms an acidic oxide. Group 13 React slowly. Aluminum forms an oxide Al displaces H2(g) from steam. Al reacts readily if the SnO can act as an coating that protects2 the metal; the protective oxide coating is acid or a base. PbO2 compound Alis2 Ounreactive.3 can act as a base or an removed, to generate H2(g) . acid. Group 14 TransitionC and Metals Si areZn non- is themetals, most and form acidicZn and The Fe most metallicZn elements, reacts readily Sn Sn and Pb react slowly to (for example, Fe, reactive transition displace H2(g) to generate H2(g), oxides. Ge is a metalloid, and forms an and Pb, do not react with water. form H2(g). Co, Ni, Cu, Zn, metal, and forms ZnO from steam. Fe Cu, Ag, and Au acidic oxide. SnO2 can act as an acid or a Ag, Au) when the metal is rusts slowly at do not react. base. PbO is unreactive. 2 burned in air. Ag and room temperature. Transition Metals (for Zn is the mostAu reactivedo not react. , Zn and Fe displace H2(g) Zn reacts readily to generate example, Fe, Co, Ni, Cu, and forms ZnO when the metal is burned from steam. Fe rusts slowly at H2(g), Cu, Ag, and Au do not Zn, Ag, Au) in air. Ag and Au do not react. room temperature. react.

Magnesium ribbon reacting Potassium reacting Nickel reacting with with oxygen in air with water dilute acid

Chapter 3 , , and Periodic Trends • MHR 155 Periodic Trends in Atomic Radius As you know, atoms are not solid spheres. Their volumes (the extent of their orbitals) are described in terms of probabilities. Nevertheless, the size of an — its atomic radius — is a measurable property. Chemists can determine it by measuring the distance between the nuclei of bonded, neighbouring atoms. For example, for metals, atomic radius is half the Atomic Radius distance between neighbouring nuclei in a crystal of the metal element. For elements that occur as , which is the case for many non- metals, atomic radius is half the distance between nuclei of identical atoms that bonded together with a single covalent bond. In Figure 3.23, the radii of metallic elements represent the radius of an atom in a metallic The size of an atom, its atomic radius, decreases crystal.across The radiia period. of all other elementsFurthermore, represent the radius atomic of an atom radii of the element participating in a single covalent bond with one additional, generally increase down a group. Two factors affectlike atom. differences in atomic radii:

1 8 (IA) (VIIIA) H 37 He 31

1 2 3 4 5 6 7 (IIA) (IIIA) (IVA) (VA) (VIA) (VIIA) Li152 Be 112 BC85 77 N 75 OF73 72 Ne 71 2 1.As n increases, there is a higher probability of Na186 Mg 160 Al143 Si 118 P 110 S103 Cl 100 Ar 98 finding electrons farther from their nucleus. 3 Therefore, the atomic volume is larger. K227 Ca 197 Ga135 Ge 122 As 120 Se119 Br 114 Kr 112 4 Period

2.The other factor that affects atomic radii is Rb248 Sr 215 In167 Sn 140 Sb 140 TeI142 133 Xe 131 changing nuclear charge — specifically, the 5

(the net force of Cs265 Ba 222 Tl170 Pb 146 Bi 150 Po 168At (140) Rn(140) attraction between electrons and the nucleus) 6

Fr (270)Ra (220) 7

3 4 5 6 7 8 9 10 11 12 (IIIB) (IVB) (VB) (VIB) (VIIB) (VIIIB) (IB) (IIB) Sc162 Ti 147 V134 Cr 128 Mn127 Fe 126 Co 125 Ni124 Cu 128 Zn 134 4

Y180 Zr 160 Nb146 Mo 139 Tc136 Ru 134 Rh 134 Pd137 Ag 144 Cd 151 5

La 187 Hf 159 TaW146 139 Re137 Os 135 Ir 136 Pt138 Au 144 Hg 151 6

Figure 3.23 Representations of atomic radii for main group and transition elements. (Values for atomic radii are given in picometres. Those in parentheses have only two significant digits.)

152 MHR • Unit 2 Structure and Properties First Ionization Energy

The energy needed to completely remove one electron from a ground state gaseous atom is called the ionization energy. Energy must be added to the atom to remove an electron in order to overcome the force of attraction exerted on the electron by the nucleus. Since multi-electron atoms have two or more electrons, they also have more than one ionization energy.

For calcium the first ionization energy (IE1), is 599 kJ/mol: Ca(g) + 599 kJ → Ca+(g) + e-

The second ionization energy (IE2) is the amount of energy required to remove the second electron. For calcium, it may be represented as: Ca+(g) + 1145 kJ → Ca2+1(g) + e-

For a given element, IE2 is always greater than IE1 because it is always more difficult to remove a negatively charged electron from a positively charged than from the corresponding neutral atom.

Ionization measure how strongly electrons are bound to atoms. Ionization always requires energy to remove an electron from the attractive force of the nucleus. Low ionization energies indicate easy removal of electrons, and hence easy positive ion (cation) formation. First Ionization Energy Every element exhibits a large increase in ionization energy when an inner electron is removed. This supports the idea that only the outermost electrons are involvedSECTION 7.4in theIonization chemical Energy 261

bondings andGO reactions. FIGURE The inner electrons are too tightly bound to the nucleusWhich to hasbe a lostlarger firstfrom ionization the energy, atom Ar or orAs? Why?even shared with another atom.

H 1312

Be 899 Li He 520 2372 Mg Na 738 496 Ne Ca K Sc 2081 419 590 Ti N F 633 1402 1681 659 V C O Rb Sr 651 Cr B 1086 403 549 Y Mn 1314 600 Zr 653 717 Fe 801 640 Nb 763 Co Cs Ba 652 Mo Lu 684 Tc 760 Ni P Ar Ionization energy (kJ/mol) 376 503 Hf Ru Si Cl 1521 524 659 Ta 702 737 Cu Zn Al 1012 S 761 W 710 Rh 746 906 578 786 1251 770 720 Pd 1000 Re Os 760 804 Ag Cd Ge As Kr 840 Ir 731 Ga 947 Se Br 1A 880 Pt 868 579 762 1140 1351 2A 870 Au Hg 941 890 1007 In Sn Sb 558 709 834 Te I Xe 869 1008 1170 Tl Pb 589 716 Bi Po 703 Rn 812 1037 Increasing ionization energy 3A 4A 5A 6A 7A Increasing ionization energy 8A į FIGURE 7.9 Trends inTrends first ionization in first energies ionization of the elements. energies of the elements.

between the electron and the nucleus. As this attraction increases, it becomes more difficult to remove the electron and, thus, the ionization energy increases. As we move across a pe- riod, there is both an increase in effective nuclear charge and a decrease in atomic radius, GO FIGURE causing the ionization energy to increase. As we move down a column, the atomic radius in- Explain why it is easier to remove creases while the effective nuclear charge increases rather gradually. Thus, the attraction be- a 2p electron from an oxygen atom tween the nucleus and the electron decreases, causing the ionization energy to decrease. than from a nitrogen atom. The irregularities in a given period are subtle but still readily explained. For exam- ple, the decrease in ionization energy from beryllium ([He]2s2) to boron ([He]2s22p1), 2p shown in Figure 7.9, occurs because the third of B must occupy the 2p Oxygen subshell, which is empty for Be. Recall that the 2p subshell is at a higher energy than the 2s subshell (Figure 6.24). The decrease in ionization energy when moving from nitrogen 2p 2 3 2 4 ([He]2s 2p ) to oxygen ([He]2s 2p ) is because of the repulsion of paired electrons in Nitrogen the p4 configuration (Ǡ FIGURE 7.10). Remember that according to Hund’s rule, each į FIGURE 7.10 2p orbital filling in electron in the p3 configuration resides in a different p orbital, which minimizes the nitrogen and oxygen. electron–electron repulsion among the three 2p electrons. •(Section 6.8)

SAMPLE EXERCISE 7.6 Periodic Trends in Ionization Energy Referring to a periodic table, arrange the atoms Ne, Na, P,Ar, K in order of increasing first ion- ization energy.

SOLUTION Analyze and Plan We are given the chemical symbols for five elements. To rank them ac- cording to increasing first ionization energy, we need to locate each element in the periodic table. We can then use their relative positions and the trends in first ionization energies to pre- dict their order. 180 CHAPTER 5 • CHEMICAL P E R I O DIC ITY

Table 5-1 First Ionization Energies (kJ/mol of atoms) of Some Elements H He 1312 2372 Li Be B C N O F Ne 520 899 801 1086 1402 1314 1681 2081 Na Mg Al Si P S Cl Ar 496 738 578 786 1012 1000 1251 1521 K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr 419 599 631 658 650 652 717 759 758 757 745 906 579 762 947 941 1140 1351 Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe 403 550 617 661 664 685 702 711 720 804 731 868 558 709 834 869 1008 1170 Cs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn 377 503 538 681 761 770 760 840 880 870 890 1007 589 715 703 812 890 1037

Increase ionization energies indicate easy removal of electrons, and hence easy positive ion (cation) formation. Figure 5-2 shows a plot of first ionization energy versus atomic number for several elements.

First IE Elements with low ionization energies (IE) easily lose electrons to form cations. Decrease

Figure 5-2 shows that each has the highest first ionization energy in its General trends in first ionization energies of period. This should not be surprising because the noble gases are known to be very unre- A group elements with position in the active elements. It requires more energy to remove an electron from a helium atom periodic table. Exceptions occur at Groups (slightly less than 4.0 3 10218 J/atom, or 2372 kJ/mol) than to remove one from a neutral 3A and 6A. atom of any other element.

He(g) 1 2372 kJ h He1(g) 1 e2 (q1 )(q2 ) ▶ By Coulomb’s Law, F ~ , d2 The Group 1A metals (Li, Na, K, Rb, Cs) have very low first ionization energies. Each of the attraction for the outer shell these elements has only one electron in its outermost shell (. . . ns1 ), and they are the largest electrons is directly proportional to atoms in their periods. The first electron added to a shell is easily removed to form a noble the effective charges and inversely gas configuration. As we move down the group, the first ionization energies become smaller. proportional to the square of the The force of attraction of the positively charged nucleus for electrons decreases as the square distance between the charges. Even of the distance between them increases. So as atomic radii increase in a given group, first though the effective nuclear charge increases going down a group, the ionization energies decrease because the outermost electrons are farther from the nucleus. greatly increased size causes a weaker Effective nuclear charge, Zeff, increases going from left to right across a period. The in- net attraction for the outer electrons crease in effective nuclear charge causes the outermost electrons to be held more tightly, and thus results in a lower first Firstmaking Ionization them harder to remove.Energy The first ionization energies therefore generally increase ionization energy. from left to right across the periodic table. The reason for the trend in first ionization ener-

Period 2 Period 3 Period 4

2500 He Figure 5-2 A plot of first ionization Ne energies for the first 38 elements 2000 versus atomic number. The noble F gases have very high first ionization Ar 1500 N Kr energies, and the 1A metals have low Cl Br first ionization energies. Note the H O P Be C similarities in the variations for the 1000 Zn As Mg S Fe Ni Se Period 2 elements, 3 through 10, Cr Si Ca Ti to those for the Period 3 elements, B Mn Co Cu Ge Sr Sc V First ionization energy (kJ/mol) 500 Ga 11 through 18, as well as for the Li Na Al later A group elements. Variations for K Rb B group elements are not nearly so 0 pronounced as those for 5 10 15 20 25 30 35 A group elements. Atomic number

Unless otherwise noted, all content on this page is © Cengage Learning.

Copyright 2013 Cengage Learning. FirstAll Rights ionization Reserved. May energies not be copied, vs scanned, atomic or duplicated, number in wholefor orthe in part.first Due 38 to electronic elements rights, of some the third P.T.E. party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. The noble gases have very high IE1 while the 1A metals (Li, Na, K and Rb) have low IE1. Note the similarities in the variations for the Period 2 elements to those for the Period 3 elements. Variations for B group elements are not nearly so pronounced as those for A group elements. 10663_05_ch05_p173-206.indd 180 12/7/12 4:56 PM The first ionization energy of an atom is a measure of the energy change when removing an electron from the atom to form a cation.

For example, the first ionization energy of Cl(g), 1251 kJ/mol, is the energy change associated with the process Cl(g) + 1251 kJ → Cl+(g) + e-

[Ne]3s23p5 [Ne]3s23p4 The positive ionization energy means that energy must be put into the atom to remove the electron.

Most atoms can also gain electrons to form anions. The energy change that occurs when an electron is added to a gaseous atom is called the electron affinity because it measures the attraction, or affinity, of the atom for the added electron. For most atoms, energy is released when an electron is added

For example, the addition of an electron to a atom is accompanied by an energy change of -349 kJ/mol, the negative sign indicating that energy is released during the process Cl(g) - 349 kJ → Cl-(g) - e-

[Ne]3s23p5 [Ne]3s23p6 Therefore the electron affinity of Cl is -349 kJ/mol.

Ionization energy measures the ease with which an atom loses an electron, whereas electron affinity measures the ease with which an atom gains an electron. Electron affinity For the electron affinity the trends through the P.T.E. are not as evident as they are for ionization 264 CHAPTER 7 Periodic Properties of the Elements energy. The , which miss one electron to complete the p orbital, have the most negative electron affinities. By gaining an electron, a atom forms a stable anion thatThe has fact a noble-gasthat the electron configuration. affinity is positive means that an electron will not attach itself GO FIGURE to an Ar atom; the Ar- ion is unstable and does not form. The addition of an electronWhich to a nobleof the gasgroups requires shown that thehere electron resideǡ FIGUREin a higher-energy 7.11 shows orbital the electron affinities for the s- and p- elements of that is empty in the atom.has Because the mostoccupying negative a higher-energy electron orbital isthe energetically first five periods. unfavorable, Notice the that the trends are not as evident as they are for ionization electron affinity is highly positive.affinities? Why does this make energy. The halogens, which are one electron shy of a filled p subshell, have the most- sense? negative electron affinities. By gaining an electron, a halogen atom forms a 1A 8A stable anion that has a noble-gas configuration (Equation 7.5). The addi- H He tion of an electron to a noble gas, however, requires that the electron reside Ϫ73 2A 3A 4A 5A 6A 7A Ͼ 0 in a higher-energy subshell that is empty in the atom (Equation 7.6). Li Be B C N O F Ne Because occupying a higher-energy subshell is energetically unfavorable, Ϫ60 Ͼ 0 Ϫ27 Ϫ122 Ͼ 0 Ϫ141 Ϫ328 Ͼ 0 the electron affinity is highly positive. The electron affinities of Be and Mg Na Mg Al Si P S Cl Ar are positive for the same reason; the added electron would reside in a previ- Ϫ53 Ͼ 0 Ϫ43 Ϫ134 Ϫ72 Ϫ200 Ϫ349 Ͼ 0 ously empty p subshell that is higher in energy. K Ca Ga Ge As Se Br Kr The electron affinities of the group 5A elements are also interesting. Ϫ48 Ϫ2 Ϫ30 Ϫ119 Ϫ78 Ϫ195 Ϫ325 Ͼ 0 Because these elements have half-filled p subshells, the added electron Rb Sr In Sn Sb Te I Xe must be put in an orbital that is already occupied, resulting in larger Ϫ47 Ϫ5 Ϫ30 Ϫ107 Ϫ103 Ϫ190 Ϫ295 Ͼ 0 electron–electron repulsions. Consequently, these elements have electron affinities that are either positive (N) or less negative than the electron į FIGUREElectron affinity 7.11 in kJ/molElectron for some affinity elements in affinities of their neighbors to the left (P, As, Sb). Recall that in Section 7.4 kJ/mol for selected s- and p-block we saw a discontinuity in the trends for first ionization energy for the same reason. elements. Electron affinities do not change greatly as we move down a group (Figure 7.11). For F, for instance, the added electron goes into a 2p orbital, for Cl a 3p orbital, for Br a 4p orbital, and so forth. As we proceed from F to I, therefore, the average distance between the added electron and the nucleus steadily increases, causing the electron–nucleus attraction to decrease. However, the orbital that holds the outermost electron is increas- ingly spread out, so that as we proceed from F to I, the electron–electron repulsions are also reduced. As a result, the reduction in the electron–nucleus attraction is counterbal- anced by the reduction in electron–electron repulsions.

GIVE IT SOME THOUGHT What is the relationship between the value for the first ionization energy of a Cl-(g) ion and the electron affinity of Cl(g)?

7.6 | METALS, , AND Atomic radii, ionization energies, and electron affinities are properties of individual atoms. With the exception of the noble gases, however, none of the elements exist in nature as individual atoms. To get a broader understanding of the properties of ele- ments, we must also examine periodic trends in properties that involve large collections of atoms. The elements can be broadly grouped as metals, nonmetals, and metalloids (Ǡ FIGURE 7.12). •(Section 2.5) Some of the distinguishing properties of metals and nonmetals are summarized in Ĭ TABLE 7.3. In the following sections, we explore some common patterns of reactivity across the periodic table. We will examine reactivity for nonmetals and metals in more depth in later chapters.

TABLE 7.3 • Characteristic Properties of Metals and Nonmetals

Metals Nonmetals

Have a shiny luster; various colors, although most are silvery Do not have a luster; various colors Solids are malleable and ductile Solids are usually brittle; some are hard, some are soft Good conductors of heat and electricity Poor conductors of heat and electricity Most metal oxides are ionic solids that are basic Most oxides are molecular substances that form acidic solutions Tend to form cations in aqueous solution Tend to form anions or oxyanions in aqueous solution Metals, Nonmetals and Metalloids With the exception of the noble gases, however, none of the elements exist in nature as individual atoms. The elements can be broadly grouped,SECTION 7.6consideringMetals, Nonmetals, and Metalloids 265 the properties, as metals, nonmetals, and metalloids. GO FIGURE Notice that germanium, Ge, is a metalloid but tin, Sn, is a metal. What changes in atomic properties do you think are important in explaining this difference?

Increasing metallic character 1A 8A 1 18 1 2A 2 H 3A 4A 5A 6A 7A 2 13 14 15 16 17 He 3 4 5 6 7 8 9 10 Li Be B C N O F Ne 8B 11 12 3B 4B 5B 6B 7B 1B 2B 13 14 15 16 17 18 Na Mg 3 4 5 6 7 8910 11 12 Al Si P S Cl Ar 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe 55 56 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 Cs Ba Lu Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn

Increasing metallic character 87 88 103 104 105 106 107 108 109 110 111 112 113114 115 116 117 118 Fr Ra Lr Rf Db Sg Bh Hs Mt Ds Rg Cp

Metals 57 58 59 60 61 62 63 64 65 66 67 68 69 70 La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Metalloids 89 90 91 92 93 94 95 96 97 98 99 100 101 102 Nonmetals Ac Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No

į FIGURE 7.12 Metals, metalloids, and nonmetals.

The more an element exhibits the physical and chemical properties of metals, the greater its metallic character. As indicated in Figure 7.12, metallic character generally increases as we proceed down a group of the periodic table and decreases as we proceed right across a period. Let’s now examine the close relationships that exist between elec- tron configurations and the properties of metals, nonmetals, and metalloids.

Metals

Most metallic elements exhibit the shiny luster we associate with metals (Ǡ FIGURE 7.13). Metals conduct heat and electricity. In general they are malleable (can be pounded into thin sheets) and ductile (can be drawn into wires). All are solids at room temperature except mercury (melting point =-39 °C) , which is a liquid at room tem- perature. Two metals melt at slightly above room temperature, cesium at 28.4 °C and gallium at 29.8 °C . At the other extreme, many metals melt at very high temperatures. For example,chromium melts at 1900 °C . Metals tend to have low ionization energies (Figure 7.9) and therefore tend to form cations relatively easily. As a result, metals are oxidized (lose electrons) when they un- dergo chemical reactions. Among the fundamental atomic properties (radius, electron configuration, electron affinity, and so forth), first ionization energy is the best indicator į FIGURE 7.13 Metals are shiny and of whether an element behaves as a metal or a nonmetal. malleable. Ǡ FIGURE 7.14 shows the oxidation states of representative of metals and nonmetals. As noted in Section 2.7, the charge on any ion in a compound is always 1+ , and that on any is always 2+ . For atoms belonging to either of these groups, the outer s electrons are easily lost, yielding a noble-gas electron configuration. For metals belonging to groups with partially occupied p orbitals (groups 3A–7A), cations are formed either by losing only the outer p electrons (such as Sn2+ ) or the outer s and p electrons (such as Sn4+ ). The charge on transition-metal ions does not follow an obvious pattern. One characteristic of the transition metals is their ability to form more than one cation. For example, iron is 2+ in some compounds and 3+ in others.

GIVE IT SOME THOUGHT Describe a general relationship between trends in metallic character and trends in ionization energy. Metals, Nonmetals and Metalloids

Characteristic Properties of Metals and Nonmetals Metals Nonmetals •Have a shiny luster; various colors, although •Do not have a luster; various colors most are silvery •Solids are malleable and ductile •Solids are usually brittle; some are hard, some are soft •Good conductors of heat and electricity •Poor conductors of heat and electricity •Most metal oxides are ionic solids that are •Most nonmetal oxides are molecular substances basic that form acidic solutions •Tend to form cations in aqueous solution •Tend to form anions or oxyanions in aqueous solution SECTION 7.6 Metals, Nonmetals, and Metalloids 265

GO FIGURE Notice that germanium, Ge, is a metalloid but tin, Sn, is a metal. What changes in atomic properties do you think are important in explaining this difference?

Increasing metallic character 1A 8A 1 18 1 2A 2 H 3A 4A 5A 6A 7A 2 13 14 15 16 17 He 3 4 5 6 7 8 9 10 Li Be B C N O F Ne 8B 11 12 3B 4B 5B 6B 7B 1B 2B 13 14 15 16 17 18 Na Mg 3 4 5 6 7 8910 11 12 Al Si P S Cl Ar 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe 55 56 71 72 73 74Metals75 76 77 78 79 80 81 82 83 84 85 86 Cs Ba Lu Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn

Increasing metallic character 87 88 103 104 105 106 107 108 109 110 111 112 113114 115 116 117 118 Fr Ra Lr Rf Db Sg MostBh HsmetallicMt Ds elementsRg Cp exhibit the shiny luster and conduct heat and electricity. In general they are malleable (can be pounded into thin sheets) and ductile (can be drawn into wires). Metals 57 58 59 60 61 62 63 64 65 66 67 68 69 70 La Ce Pr AllNd arePm solidsSm Eu atGd roomTb DytemperatureHo Er Tm Ybexcept mercury. Metalloids 89 90 91 Two92 metals93 94 (Cs95 and96 Ga97 ) melt98 99 above100 room101 102 temperature. At the other extreme, many metals have very Nonmetals Ac Th Pa highU meltingNp Pu temperatures.Am Cm Bk Cf ForEs example,Fm Md chromiumNo melts at 1900 °C. į FIGURE 7.12 Metals, metalloids, and nonmetals. SECTION 7.7 Trends for Group 1A and Group 2A Metals 269

Metals tend to have lowTABLE IE and 7.4 tend• Some to Properties form of thecations Alkali Metals. + The charge on any alkali metal ionElectron in a compoundMelting is alwaysDensity 1 , Atomicand that onI1 any alkaline earth metal is The more an element exhibits the physical and chemical properties of metals, the 3 + Element Configuration Point (°C) (g/cm ) Radius (Å) (kJ/mol) greater its metallic character. Asalways indicated 2 ,in that Figure is, the7.12, outer metallic s electrons character generallyare easily lost. Lithium [He]2s1 181 0.53 1.34 520 Compounds made up of a metal and a nonmetalSECTION 7.6 tendMetals, to Nonmetals,be ionic and substances Metalloids 265 increases as we proceed down a group of the periodic table andSodium decreases[Ne]3 as wes1 proceed98 0.97 1.54 496 right across a period. Let’s now examine the close relationshipsPotassium that exist[Ar]4 betweens1 elec-63 0.86 1.96 419 GO FIGURE Rubidium [Kr]5s1 39 1.53 2.11 403 tron configurations and the propertiesNoticeAmong that ofgermanium, metals,the fundamental nonmetals,Ge, is a metalloid atomic and but metalloids. tin, properties Sn, is a metal. (radius, What changes electron configuration, etc.), first ionization energy is the best 1 in atomicindicator properties of whetherdo you think an are element importantCesium inbehaves explaining[Xe]6s as this a difference?metal28 or a nonmetal.1.88 2.25 376 Increasing metallic character Metals 1A Group 1A: The Alkali Metals 8A 1 18 1 2A The alkali metals are softǠ metallicFIGURE solids (Ǡ FIGURE2 7.19). All have characteristic metallic Most metallic elements exhibit theH shiny luster we associate with metals (3A 4A 5A 6A 7A 2 properties, such as a silvery,13 14 metallic15 16 luster17 andHe high thermal and electrical conductivity. 7.13). Metals conduct heat and electricity.3 4 In general they are malleable5 (can6 7 be8 9 10 Li Be The name alkali comesB fromC an ArabicN O wordF meaningNe “ashes.”Many compounds of sodium pounded into thin sheets) and ductile (can be drawn into wires).8B All are solids at room 11 12 3B 4B 5B 6B 7B and potassium,1B two2B alkali13 metals,14 15 were16 isolated17 18 from wood ashes by early chemists. temperature except mercury (meltingNa Mgpoint3 =-4 539 6°C)7 , which89 isAs 10 aį liquidTABLE11 12 7.4at Alshows,roomSi the tem-P alkaliS metalsCl Ar have low densities and melting points, and 19 20 21 22 23 24 25 26 these27 properties28 29 30vary 31in a 32fairly33 regular34 way35 with36 increasing atomic number. We see the perature. Two metals melt at slightlyK CaaboveSc roomTi V temperature,Cr Mn Fe Co cesiumNi Cu Znat 28.4Ga Ge °CAs andSe Br Kr 37 38 39 40 41 42 43 44 usual45 trends46 47 as we48 move49 down50 51 the group,52 53 such54 as increasing atomic radius and decreas- Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe gallium at 29.8 °C . At the other extreme, many metals melt ingat firstvery ionization high temperatures. energy. The alkali metal of any given period has the lowest I1 value in 55 56 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 For example,chromium melts at 1900Cs Ba °C .Lu Hf Ta W Re Os theIr periodPt (FigureAu Hg 7.9),Tl whichPb Bi reflectsPo theAt relativeRn ease with which its outer s electron Metals tend to have low ionizationIncreasing metallic character 87 88 energies103 104 (Figure105 106 107 7.9)108 canand109 be 110removed.therefore111 112 As tenda113 result,114 to the 115form alkali116 metals 117 118 are all very reactive, readily losing one elec- Fr Ra Lr Rf Db Sg Bh Hs tronMt toDs formRg ionsCp carrying a 1+ charge. •(Section 2.7) cations relatively easily. As a result, metals are oxidized (lose electrons)The alkali metals when exist they in nature un- only as compounds. Sodium and potassium are rela- Metals 57 58 59 60 61 62 63 64 65 66 67 68 69 70 La Ce Pr Nd PmtivelySm abundantEu Gd inTb Earth’sDy crust,Ho Er in seawater,Tm Yb and in biological systems, usually as the cations dergo chemical reactions. Among theMetalloids fundamental atomic properties (radius, electron 89 90 91 92 93 of94 ionic95 compounds.96 97 All98 alkali99 metals100 101 combine102 directly with most nonmetals. For example, configuration, electron affinity, and Nonmetalsso forth),Ac firstTh ionizationPa U Np theyenergyPu reactAm withisCm the hydrogenBk bestCf indicatortoEs formFm hydridesMd Noį andFIGURE with sulfurMetals 7.13to form are sulfides: Metalsshiny and are malleable shiny andį FIGUREElemental 7.19 Sodium, Na like the other alkali metals, is soft enough to be cut with of whether an element behavesį asFIGURE a metal 7.12 orMetals, a nonmetal. metalloids, and nonmetals. malleable. 2 M(s) + H2(g) ¡ 2 MH(s) [7.16] a knife. Ǡ FIGURE 7.14 shows the oxidation states of representative ions of metals and 2 M(s) + S(s) ¡ M2S(s) [7.17] nonmetals. As noted in Section 2.7, the charge on any alkali metal ion in a compound is The more an element exhibits the physicalwhere andM represents chemical propertiesany alkali metal.of metals, In the of the alkali metals (LiH, NaH, and so always 1+ , and that on any alkalinegreater its earthmetallic metal character is always. As indicated 2+forth), in . For Figure hydrogen atoms 7.12, is metallic belongingpresent character as H- ,to the generally ion.A hydrogen atom that has gained an either of these groups, the outerincreases s electrons as we proceed are downeasily a group lost, of yielding theelectron, periodic a this noble-gastable ion and is distinct decreases electron from as wethe proceedhydrogen ion,H+ , formed when a hydrogen atom right across a period. Let’s now examine theloses closeits electron.relationships that exist between elec- configuration. For metals belonging to groups with partially occupiedThe alkali p orbitalsmetals react (groups vigorously with water, producing hydrogen gas and a solu- tron configurations and the properties of metals, nonmetals, and metalloids.2 3A–7A), cations are formed either by losing only the outer p tionelectrons of an alkali (such metal as hydroxide: Sn + ) or 4+ the outer s and p electrons (suchMetals as Sn ). The charge on transition-metal2 M( ionss) + 2does H2O(l) ¡ 2 MOH(aq) + H2(g) [7.18] not follow an obvious pattern.Most One metallic characteristic elements exhibit of the the transitionshiny Theseluster reactionswe metals associate are is very withtheir exothermic. metals ability (Ǡ InFIGURE many cases enough heat is generated to ignite the to form more than one cation.7.13 For). Metals example, conduct iron heat is and 2 + electricity. in Hsome2,producing In generalcompounds a theyfire or are sometimes and malleable 3+ even (can an be explosion (Ĭ FIGURE 7.20). The reaction is in others. pounded into thin sheets) and ductile (canmost be drawn violent into for thewires). heavier All arealkali solids metals, at room in keeping with their lower ionization energies. temperature except mercury (melting point =-39 °C) , which is a liquid at room tem- perature. Two metals melt at slightly above room temperature, cesium at 28.4 °C and GIVE IT SOME THOUGHTgallium at 29.8 °C . At the other extreme, many metals melt at very high temperatures. For example,chromium melts at 1900 °C . Describe a general relationshipMetals between tend to have trends low ionization in metallic energies character(Figure 7.9) and and thereforetrends tend to form in ionization energy. cations relatively easily. As a result, metals are oxidized (lose electrons) when they un- dergo chemical reactions. Among the fundamental atomic properties (radius, electron configuration, electron affinity, and so forth), first ionization energy is the best indicator į FIGURE 7.13 Metals are shiny and of whether an element behaves as a metal or a nonmetal. malleable. Ǡ FIGURE 7.14 shows the oxidation states of representative ions of metals and nonmetals. As noted in Section 2.7, the charge on any alkali metal ion in a compound is always 1+ , and that on any alkaline earth metal is always 2+ . For atoms belonging to either of these groups, the outer s electrons are easily lost, yielding a noble-gas electron configuration. For metals belonging to groups with partially occupied p orbitals (groups ǡ FIGURE 7.20 The 3A–7A), cations are formed either by losing only the outer p electrons (such as Sn2+ ) or alkali metals react the outer s and p electrons (such as Sn4+ ). The charge on transition-metal ions does vigorously with water. Li Na K not follow an obvious pattern. One characteristic of the transition metals is their ability to form more than one cation. For example, iron is 2+ in some compounds and 3+ in others.

GIVE IT SOME THOUGHT Describe a general relationship between trends in metallic character and trends in ionization energy. SECTION 7.6 Metals, Nonmetals, and Metalloids 267

SAMPLE EXERCISE 7.8 Metal Oxides (a) Would you expect scandium oxide to be a solid, liquid, or gas at room temperature? (b) Write the balanced chemical equation for the reaction of scandium oxide with nitric acid. SOLUTION Analyze and Plan We are asked about one physical property of scandium oxide—its state at room temperature—and one chemical property—how it reacts with nitric acid. Solve (a) Because scandium oxide is the oxide of a metal, we expect it to be an ionic solid. Indeed it is, with the very high melting pointNonmetals of2485 °C . 3+ 2- (b) In compounds, scandium hasNonmetals a 3+ charge, canSc be , and solid, the oxide liquid, ion is or O gas . Consequently,. They are not lustrous and generally are poor the formula of scandium oxide is Sc O .Metal oxides tend to be basic and,therefore,to react conductors2 3 of heat and electricity. Their melting points are generally low (although diamond, with acids to form a salt plus water. In this case the salt is scandium nitrate, Sc(NO3)3: a form of C, melts at 3570 °C). Sc O (s) 6 HNO (aq) 2 Sc(NO ) (aq) 3 H O(l) 2 3 + Under3 ordinary¡ conditions,3 3 +seven2 nonmetals exist as diatomic molecules. Five of these are gases (H2, N2, O 2, F 2, and Cl2), one is a liquid (Br2), and one is a volatile solid (I2). Excluding the noble gases, the PRACTICE EXERCISE remaining nonmetals are solids that can be either hard, such as diamond, or soft, such as sulfur Write the balanced chemical equation for the reaction between copper(II)SECTION oxide 7.6and Metals,sulfuric Nonmetals, and MetalloidsSECTION 7.6265 Metals, Nonmetals, and Metalloids 265 acid. Because of their relatively large electron affinities, nonmetals tend to gain electrons and form anions GO FIGURE Answer: CuO(s) + H2SO4(aq) ¡whenCuSO they 4react(aq) + withGOH2 O(FIGURE metals.l) For example, the reaction of aluminum with produces the ionic Notice that germanium, Ge,compound is a metalloid aluminumNotice but tin, that Sn, bromide: germanium, is a metal. Ge,What is changesa metalloid but tin, Sn, is a metal. What changes in atomic properties do you think are importantin atomic in propertiesexplaining dothis you difference? think are important in explaining this difference? 2 Al + 3 Br2 → 2 AlBr3(s) Increasing metallic character Increasing metallic character 1A 1A 8A 8A 1 1 Nonmetals 18 18 1 1 2A 2A 3A 4A 5A 6A 7A 2 2 H H 3A 4A 5A 6A 7A Nonmetals can be 2solid, liquid, or gas. They are not lustrous2 and13 14generally15 16 are17 poorHe con- 13 14 15 16 17 He 3 4 3 4 5 6 7 8 9 10 5 6 7 8 9 10 ductors of heatLi andBe electricity. Their melting pointsLi areBe generallyB C lowerN O thanF Nethose of B C N O F Ne 8B 8B 11 12 3B 4B 5B 6B 7B 11 1B 12 2B 3B 13 4B 14 5B 15 6B 16 7B 17 18 1B 2B 13 14 15 16 17 18 metals (althoughNa Mgdiamond,3 4 a 5form6 of7 carbon,89 is10 Naan11 exceptionMg12 3 Al 4 Siand5 P melts6 S 7 atCl 893570Ar °C10 ). 11 12 Al Si P S Cl Ar Under ordinary19 conditions,20 21 22 seven23 24 nonmetals25 26 27 exist28 19 as29 diatomic20 30 21 31 22 molecules.32 23 33 24 34 25 Five35 26 36of27 these28 29 30 31 32 33 34 35 36 K Ca Sc Ti V Cr Mn Fe Co Ni K CuCa Zn Sc Ga Ti Ge V As Cr SeMnBr Fe KrCo Ni Cu Zn Ga Ge As Se Br Kr are gases (H2,N37 2,O38 2,F39 2,and40 41 Cl242), one43 is44 a liquid45 46 37(Br47238),48 and39 49 one40 50 41is 51a 42volatile52 43 53 44solid54 45 (I462). 47 48 49 50 51 52 53 54 Excluding the RbnobleSr gases,Y Zr theNb remainingMo Tc Ru nonmetalsRh PdRbAg areSr Cd solidsY In Zr thatSnNbSb canMoTe beTc eitherI Ru XeRh hard,Pd Ag Cd In Sn Sb Te I Xe 55 56 71 72 73 74 75 76 77 78 55 79 56 80 71 81 72 82 73 83 74 84 75 85 76 86 77 78 79 80 81 82 83 84 85 86 such as diamond,Cs Ba or soft,Lu Hf suchTa as WsulfurRe (ǠOs FIGUREIr Pt Cs Au7.16Ba Hg).LuTl Hf Pb Ta Bi W Po Re At Os Rn Ir Pt Au Hg Tl Pb Bi Po At Rn Increasing metallic character 87 88 103 104 105 106 107 108 109 Increasing metallic character 11087 11188 112103113104114105 115106116107 117108118109 110 111 112 Sulfur,113 114known 115 to116 the 117medieval118 world as Because ofFr theirRa relativelyLr Rf Db large,Sg Bh negativeHs Mt electronDs Fr Rg Raaffinities,Cp Lr Rf nonmetalsDb Sg Bh tendHs toMt gainDs Rg įCpFIGURE“brimstone,” 7.16 Sulfur, is a nonmetal. known to the electrons when they react with metals. For example, the reaction of aluminum with medieval world as “brimstone,” is a Metals 57 58 Compounds59 60 61 62 composed63 Metals64 65 entirely66 57 67 58of68 nonmetals59 69 60 70 61 are62 typically63 64 nonmetal.65 molecular66 67 substances68 69 70 that tend to be gases, bromine produces the ionicLa compoundCe Pr Nd aluminumPm Sm Eu bromide:Gd Tb DyLa HoCe Er Pr TmNdYbPm Sm Eu Gd Tb Dy Ho Er Tm Yb Metalloids Metalloids 89 90 liquids,91 92 or93 low-melting94 95 96 solids97 98 89 at99 room90 10091 101temperature.92 10293 94 95 E.g.96 the97 common98 99 100hydrocarbons101 102 we use for fuel Nonmetals Ac Th Pa U Np Pu Am NonmetalsCm Bk Cf Ac Es ThFmPaMd U NoNp Pu Am Cm Bk Cf Es Fm Md No 2 Al(s)(methane,+ 3 Br2(l )CH¡4; propane,2 AlBr3 C(s)3H8; octane, C8H18) and[7.12] the gases HCl, NH3, and H2S. į FIGURE 7.12 Metals, metalloids, and nonmetals.į FIGURE 7.12 Metals, metalloids, and nonmetals. A nonmetal typically will gain enough electrons to fill its outermost occupied p subshell, giving a noble-gas electron con- figuration. ForThe example,more an element the bromine exhibits the atom physical gains andThe one chemical more electron an propertieselement exhibits of metals, the thephysical and chemical properties of metals, the to fill its greater4p subshell: its metallic character. As indicated ingreater Figure its 7.12, metallic metallic character character. As generally indicated in Figure 7.12, metallic character generally increases as we proceed down a group of the increasesperiodic tableas we and proceed decreases down as a wegroup proceed of the periodic table and decreases as we proceed 2 10 5 2 10 6 Br right([Ar]4 acrosss 3 ad period.4p ) Let’s+ e now- Q examineBr- ([Ar]4 the rightcloses 3 acrossrelationshipsd 4p a period.) that Let’s exist now between examine elec- the close relationships that exist between elec- tron configurations and the properties of metals,tron nonmetals,configurations and andmetalloids. the properties of metals, nonmetals, and metalloids. Compounds composed entirely of nonmetals are typically molecularMetals substances that tend to be gases, liquids,Metals or low-melt- ing solids at room temperature. Examples include the common Most metallic elements exhibit the shiny lusterMost we metallic associate elements with metals exhibit (Ǡ theFIGURE shiny luster we associate with metals (Ǡ FIGURE hydrocarbons7.13). Metalswe use conduct for fuel heat (methane, and electricity. CH7.134; In propane, ). general Metals they conduct C3 H are8; malleable heat and (can electricity. be In general they are malleable (can be octane, Cpounded8H18) and into thinthe sheets)gases HCl,and ductile NH3 (can,and bepounded H drawn2S. Many into into wires). thin drugs sheets) All are and solids ductile at room (can be drawn into wires). All are solids at room are moleculestemperature composed except mercury of C, H,(melting N, O, point andtemperature=- other39 °C) nonmetals. , whichexcept is mercury a liquid (meltingat room tem-point =-39 °C) , which is a liquid at room tem- For example,perature. the Two molecular metals melt formula at slightly for above the perature.room drug temperature, Celebrex Two metals cesiumis melt atat slightly28.4 °C above and room temperature, cesium at 28.4 °C and gallium at 29.8 °C . At the other extreme, manygallium metals at melt29.8 °Cat .very At the high other temperatures. extreme, many metals melt at very high temperatures. C17H14F3ForN3 example,chromiumO2S. Most nonmetal melts oxides at 1900 are °C . acidic,For example,chromiumwhich means melts at 1900 °C . that those thatMetals dissolve tend to in have water low ionizationform acids: energies (FigureMetals 7.9)tend andto have therefore low ionization tend to form energies (Figure 7.9) and therefore tend to form cations relatively easily. As a result, metals arecations oxidized relatively (lose electrons)easily. As awhen result, they metals un- are oxidized (lose electrons) when they un- į FIGURE 7.17 The reaction of CO Nonmetaldergo chemical oxide reactions.+ water Among¡ theacid fundamentaldergo chemical atomic properties reactions. (radius, Among electronthe fundamental atomic properties (radius, electron 2 with water containing a bromthymol blue configuration, electron affinity, and so forth),configuration, first ionization electron energy isaffinity, the best and indicator so forth), first ionization energy is the best indicator CO2(g) + H2O(l) ¡ H2CO3(aq) [7.13] į FIGUREindicator. 7.13 MetalsInitially, are shiny the and blue colorį FIGUREtells us the 7.13 Metals are shiny and of whether an element behaves as a metal or aof nonmetal. whether an element behaves as a metal or amalleable. nonmetal. water is slightly basic. When a malleable.piece of solid Ǡ FIGURE 7.14 shows the oxidation states Ǡ ofFIGURE representative 7.14 shows ions of the metals oxidation and states of representative ions of metals and P 4O10(s) + 6 H2O(l) ¡ 4 H3PO4(aq) [7.14] carbon dioxide (“dry ice”) is added, the color nonmetals. As noted in Section 2.7, the chargenonmetals. on any alkali As notedmetal inion Section in a compound 2.7, the charge is on any alkali metal ion in a compound is changes to yellow, indicating an acidic The alwaysreaction 1+ ,of and carbon that on dioxide any alkaline with earth water metalalways (Ǡ isFIGURE always1+ , and 2 +that 7.17 . For on )atoms accountsany alkaline belonging for earth theto metal acidity is always 2+ . For atoms belonging to either of these groups, the outer s electrons areeither easily of lost, these yielding groups, a the noble-gas outer s electronselectron are easily lost,solution. yielding The a noble-gas mist is waterelectron droplets of carbonated water and, to some extent, rainwater. Because sulfur is present in oil and coal, condensed from the air by the cold CO gas. combustionconfiguration. of these For common metals belonging fuels produces to groupsconfiguration. with sulfur partially dioxide Foroccupied metals and p belonging sulfurorbitals trioxide.(groups to groups These with partially occupied p orbitals (groups 2 3A–7A), cations are formed either by losing only3A–7A), the outer cations p electrons are formed (such either as Snby2 losing+ ) or only the outer p electrons (such as Sn2+ ) or the outer s and p electrons (such as Sn4+ ).the The outercharge s andon transition-metalp electrons (such ions as Sndoes4+ ). The charge on transition-metal ions does not follow an obvious pattern. One characteristicnot follow of the antransition obvious metals pattern. is Onetheir characteristic ability of the transition metals is their ability to form more than one cation. For example,to iron form is more2+ in than some one compounds cation. For and example, 3+ iron is 2+ in some compounds and 3+ in others. in others.

GIVE IT SOME THOUGHT GIVE IT SOME THOUGHT Describe a general relationship between trendsDescribe in metallic a general character relationship and trends between trends in metallic character and trends in ionization energy. in ionization energy. 268 CHAPTER 7 Periodic Properties of the Elements

substances dissolve in water to produce acid rain,a major pollutant in many parts ofthe world. Like acids, most nonmetal oxides dissolve in basic solutions to form a salt plus water: Nonmetal oxide + base ¡ salt + water

CO2(g) + 2 NaOH(aq) ¡ Na2CO3(aq) + H2O(l) [7.15]

GIVE IT SOME THOUGHT

A compound ACl3 (A is an element) has a melting point of -112 °C . Would you expect the compound to be molecular or ionic? If you were told that A is either scandium or phosphorus, which do you think is the more likely choice?

SAMPLE EXERCISE 7.9 Nonmetal Oxides

Write the balanced chemical equation for the reaction of solid selenium dioxide, SeO2(s), with (a) water, (b) aqueous sodium hydroxide.

SOLUTION Analyze and Plan We note that selenium is a nonmetal. We therefore need to write chemical equations for the reaction of a nonmetal oxide with water and with a base, NaOH. Nonmetal oxides are acidic, reacting with water to form an acid and with bases to form a salt and water. Solve (a) The reaction between selenium dioxide and water is like that between carbon dioxide and water (Equation 7.13):

SeO2(s) + H2O(l) ¡ H2SeO3(aq)

(It does not matter that SeO2 is a solid and CO2 is a gas under ambient conditions; the point is that both are water-soluble nonmetal oxides.) (b) The reaction with sodium hydroxide is like the reaction in Equation 7.15:

SeO2(s) + 2 NaOH(aq) ¡ Na2SeO3(aq) + H2O(l)

PRACTICE EXERCISE Write the balanced chemical equation for the reaction of solid tetraphosphorus hexoxide with Metalloids water. Answer: P4O6(s) + 6 H2O(l) ¡ 4 H3PO3(aq) Metalloids have properties intermediate between those of metals and those of nonmetals. They may have some characteristic metallic properties but lack others. E.g. Silicon looks like a metal, but it is brittle rather than malleable and does not conduct heat or Metalloids electricity nearly as well as metals do Metalloids have properties intermediate between those of metals and those of nonmetals. They may have some characteristic metallic properties but lack others. For example, the Several metalloids, e.g. Silicon, are electrical semiconductors and are metalloid silicon looks like a metal (ǡ FIGURE 7.18), but it is brittle rather than mal- the principal components of circuits and computer chips. One of the leable and does not conduct heat or electricity nearly as well as metals do. Compounds of reasons is that their electrical conductivity is intermediate between metalloids can have characteristics of the compounds of metals or nonmetals. that of metals and that of nonmetals. Several metalloids, most notably silicon, are electrical semiconductors and are the principal elements used in integrated circuits and computer chips. One of the reasons metalloids can be used for integrated circuits is that their electrical conductivity is inter- Elemental Si looks metallic but is brittle and mediate between that of metals and that of nonmetals. Very pure silicon is an electrical į FIGUREhas low thermal 7.18 andElemental electrical conductivity. silicon. insulator, but its conductivity can be dramatically increased with the addition of specific Although it looks metallic, silicon, a impurities called dopants.This modification provides a mechanism for controlling the metalloid, is brittle and a poor thermal electrical conductivity by controlling the chemical composition. We will return to this and electrical conductor. point in Chapter 12.

7.7 TRENDS FOR GROUP 1A AND Very pure silicon is an electrical insulator, but its conductivity can be dramatically increased with the | addition of specific impurities called dopants. This modification provides a mechanism for controlling the GROUP 2A METALS electrical conductivity by controlling the chemical composition. As we have seen, elements in a given group possess general similarities. However, trends also exist within each group. In this section we use the periodic table and our knowledge of electron configurations to examine the chemistry of the alkali metals and alkaline earth metals.