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Chapter 7 Periodic Properties of the Elements © 2012 Pearson Education, Inc. Development of Periodic Table Dmitri Mendeleev and Lothar Meyer independently came to the same conclusion about how elements should be grouped. © 2012 Pearson Education, Inc. Periodic Properties of the Elements Development of the Periodic Table Mendeleev, for instance, predicted the discovery of germanium (which he called eka-silicon) as an element with an atomic weight between that of zinc and arsenic, but with chemical properties similar to those of silicon. Periodic © 2012 Pearson Education, Inc. Properties of the Elements A. B. C. D. Lanthanides because some of the elements are not stable Row 6, missing atomic numbers of elements between Ba and Lu Row 6, Rn is the start of elements that are radioactive Periodic Properties Row 7, elements in this row are generally radioactive © 2012 Pearson Education, Inc. of the Elements A. B. C. D. Atomic weight has uncertainty in measurement, whereas atomic number depends only on number of protons. Atomic weight depends both on number of protons and neutrons. Atomic weight is greatly influenced by number of electrons, not protons. Atomic weight depends both on number of protons and electrons. © 2012 Pearson Education, Inc. Periodic Properties of the Elements A. B. C. D. Co/Ni Th/Pa Te/I All of the above © 2012 Pearson Education, Inc. Periodic Properties of the Elements Periodic Trends • In this chapter, we will rationalize observed trends in – Sizes of atoms and ions. – Ionization energy. – Electron affinity. © 2012 Pearson Education, Inc. Periodic Properties of the Elements Effective Nuclear Charge • In a many-electron atom, electrons are both attracted to the nucleus and repelled by other electrons. • The nuclear charge that an electron experiences depends on both factors. The effective nuclear charge, Zeff, is found this way: Zeff = Z − S where Z is the atomic number and S is a screening constant, usually close to the number of inner electrons. © 2012 Pearson Education, Inc. Periodic Properties of the Elements A. 2s B. 2p © 2012 Pearson Education, Inc. Periodic Properties of the Elements A. B. C. D. 2p electron of a Ne atom 3s electron of a Na atom Both experience the same effective nuclear charge Requires a table of shielding constants to make an estimation © 2012 Pearson Education, Inc. Periodic Properties of the Elements What Is the Size of an Atom? The bonding atomic radius is defined as one-half of the distance between covalently bonded nuclei. © 2012 Pearson Education, Inc. Periodic Properties of the Elements Sizes of Atoms The bonding atomic radius tends to — Decrease from left to right across a row (due to increasing Zeff). — Increase from top to bottom of a column (due to the increasing value of n). © 2012 Pearson Education, Inc. Periodic Properties of the Elements A. B. C. D. Bottom and left Bottom and right Top and left Top and right © 2012 Pearson Education, Inc. Periodic Properties of the Elements Sample Exercise 7.1 Bond Lengths in a Molecule Natural gas used in home heating and cooking is odorless. Because natural gas leaks pose the danger of explosion or suffocation, various smelly substances are added to the gas to allow detection of a leak. One such substance is methyl mercaptan, CH3SH. Use Figure 7.6 to predict the lengths of the C—S, C—H, and S—H bonds in this molecule. FIGURE 7.6 Trends in bonding atomic radii for periods 1 through 5. © 2012 Pearson Education, Inc. Periodic Properties of the Elements A. B. C. D. Trends work with each other but trend in orbital size is more important. Trends work with each other but trend in effective nuclear charge is more important. Trends work against each other but trend in orbital size is more important. Trends work against each other but trend in effective nuclear charge is more important. © 2012 Pearson Education, Inc. Periodic Properties of the Elements Sample Exercise 7.2 Atomic Radii Referring to a periodic table, arrange (as much as possible) the atoms 15P, 16S, 33As, and 34Se in order of increasing size. (Atomic numbers are given to help you locate the atoms quickly in the table.) © 2012 Pearson Education, Inc. Periodic Properties of the Elements Sizes of Ions • • • © 2012 Pearson Education, Inc. Ionic size depends upon – The nuclear charge. – The number of electrons. – The orbitals in which electrons reside. Cations are smaller than their parent atoms: – The outermost electron is removed and repulsions between electrons are reduced. Anions are larger than their parent atoms” – Electrons are added and repulsions between electrons are increased. Periodic Properties of the Elements Sizes of Ions • Ions increase in size as you go down a column: – This increase in size is due to the increasing value of n. © 2012 Pearson Education, Inc. Periodic Properties of the Elements Sizes of Ions • In an isoelectronic series, ions have the same number of electrons. • Ionic size decreases with an increasing nuclear charge. © 2012 Pearson Education, Inc. Periodic Properties of the Elements A. B. C. D. © 2012 Pearson Education, Inc. Minimal change Larger Smaller Trend varies by column Periodic Properties of the Elements Sample Exercise 7.3 Atomic and Ionic Radii Arrange Mg2+, Ca2+, and Ca in order of decreasing radius.. © 2012 Pearson Education, Inc. Periodic Properties of the Elements Sample Exercise 7.4 Ionic Radii in an Isoelectronic Series Arrange the ions K+, Cl–, Ca2+, and S2– in order of decreasing size. © 2012 Pearson Education, Inc. Periodic Properties of the Elements Ionization Energy • The ionization energy is the amount of energy required to remove an electron from the ground state of a gaseous atom or ion. – The first ionization energy is that energy required to remove the first electron. – The second ionization energy is that energy required to remove the second electron, etc. © 2012 Pearson Education, Inc. Periodic Properties of the Elements A. B. C. D. First ionization step, because it takes more energy and hence shorter wavelength. First ionization step, because it takes less energy and hence shorter wavelength. Second ionization step, because it takes more energy and hence shorter wavelength. Periodic Second ionization step, because it takes less energy andProperties hence shorter wavelength. of the © 2012 Pearson Education, Inc. Elements Ionization Energy • It requires more energy to remove each successive electron. • When all valence electrons have been removed, the ionization energy takes a quantum leap. © 2012 Pearson Education, Inc. Periodic Properties of the Elements A. B. C. I1 for the boron atom is equal to I2 for the carbon atom. I2 for the carbon atom is greater. I1 for the boron atom is greater. © 2012 Pearson Education, Inc. Periodic Properties of the Elements Sample Exercise 7.5 Trends in Ionization Energy Three elements are indicated in the periodic table in the margin. Which one has the largest second ionization energy? © 2012 Pearson Education, Inc. Periodic Properties of the Elements Trends in First Ionization Energies • As one goes down a column, less energy is required to remove the first electron. – For atoms in the same group, Zeff is essentially the same, but the valence electrons are farther from the nucleus. © 2012 Pearson Education, Inc. Periodic Properties of the Elements Trends in First Ionization Energies • Generally, as one goes across a row, it gets harder to remove an electron. – As you go from left to right, Zeff increases. • However, there are two apparent discontinuities in this trend. © 2012 Pearson Education, Inc. Periodic Properties of the Elements Trends in First Ionization Energies • The first occurs between Groups IIA and IIIA. • In this case the electron is removed from a p orbital rather than an s orbital. – The electron removed is farther from the nucleus. – There is also a small amount of repulsion by the s electrons. © 2012 Pearson Education, Inc. Periodic Properties of the Elements Trends in First Ionization Energies • The second discontinuity occurs between Groups VA and VIA. – The electron removed comes from a doubly occupied orbital. – Repulsion from the other electron in the orbital aids in its removal. © 2012 Pearson Education, Inc. Periodic Properties of the Elements A. B. C. D. As; outer electrons experience larger Zeff than those in Ar. As; outer electrons experience smaller Zeff than those in Ar. Ar; outer electrons experience larger Zeff than those in As. Ar; outer electrons experience smaller Zeff than those in As. © 2012 Pearson Education, Inc. Periodic Properties of the Elements A. The 2p electron removed from an oxygen atom is in a fully occupied orbital with decreased electron-electron repulsions compared to the one from a nitrogen atom. B. The 2p electron removed from an oxygen atom is in a more than half-filled subshell, which has extra stability compared to the one from a nitrogen atom. C. The 2p electron removed from an oxygen atom is in a fully occupied orbital with increased electron-electron repulsions compared to the one from a nitrogen atom. Periodic D. The 2p electron removed from an oxygen atom is in a lower energy Properties state compared to the one from a nitrogen atom. of the © 2012 Pearson Education, Inc. Elements 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 ionization energy. FIGURE 7.9 Trends in first ionization energies of the elements © 2012 Pearson Education, Inc. Periodic Properties of the Elements A. B. Same electron configurations: [Ar]3d3 Different electron configurations © 2012 Pearson Education, Inc. Periodic Properties of the Elements Sample Exercise 7.7 Electron Configurations of Ions Write the electron configuration for (a) Ca2+, (b) Co3+, and (c) S2–. © 2012 Pearson Education, Inc. Periodic Properties of the Elements Electron Affinity Electron affinity is the energy change accompanying the addition of an electron to a gaseous atom: Cl + e− Cl− © 2012 Pearson Education, Inc. Periodic Properties of the Elements Trends in Electron Affinity In general, electron affinity becomes more exothermic as you go from left to right across a row. There are again, however, two discontinuities in this trend. © 2012 Pearson Education, Inc. Periodic Properties of the Elements Trends in Electron Affinity • The first occurs between Groups IA and IIA. – The added electron must go in a p orbital, not an s orbital. – The electron is farther from the nucleus and feels repulsion from the s electrons. © 2012 Pearson Education, Inc. Periodic Properties of the Elements Trends in Electron Affinity • The second discontinuity occurs between Groups IVA and VA. – Group VA has no empty orbitals. – The extra electron must go into an already occupied orbital, creating repulsion. © 2012 Pearson Education, Inc. Periodic Properties of the Elements A. Group 4A; outer electrons of atoms in this family experience greater Zeff than the elements in other families of the same period and this results in greater attraction of an electron when electrons are added. B. Group 5A; outer electrons of atoms in this family experience greater Zeff than the elements in other families of the same period and this results greater attraction of an electron when electrons are added. C. Group 6A; outer electrons of atoms in this family experience greater Zeff than the elements in other families of the same period and this results in greater attraction of an electron when electrons are added. D. Group 7A; outer electrons of atoms in this family experience greater Zeff than the elements in other families of the same period and this results in greater attraction of an electron when an electron is added. © 2012 Pearson Education, Inc. Periodic Properties of the Elements A. B. C. D. EA for Cl is significantly more endothermic than IE1 for Cl. IE1 for Cl– is significantly more exothermic than EA for Cl. They are equal in magnitude and opposite in sign. They are equal in magnitude and sign. © 2012 Pearson Education, Inc. Periodic Properties of the Elements Properties of Metal, Nonmetals, and Metalloids © 2012 Pearson Education, Inc. Periodic Properties of the Elements A. Electron affinity is increasing from Ge to Sn and this correlates with increasing metallic character. B. Ionization energy is decreasing from Ge to Sn and this correlates with increasing metallic character. C. Atomic radius is decreasing from Ge to Sn and this correlates with increasing metallic character. Periodic Properties D. Number of valence electrons is increasing from Ge to Sn and this correlates with of the increasing metallic character. © 2012 Pearson Education, Inc. Elements Metals versus Nonmetals Differences between metals and nonmetals tend to revolve around these properties. © 2012 Pearson Education, Inc. Periodic Properties of the Elements Metals versus Nonmetals • Metals tend to form cations. • Nonmetals tend to form anions. © 2012 Pearson Education, Inc. Periodic Properties of the Elements Metals Metals tend to be lustrous, malleable, ductile, and good conductors of heat and electricity. © 2012 Pearson Education, Inc. Periodic Properties of the Elements A. Cations are to the right of the red line and anions are to the left B. Higher oxidation states are adjacent to the red line and decrease moving to the right or left, excluding the transition elements in terms of trend in oxidation states. C. Higher oxidation states are adjacent to the red line and increase moving to the right or left, excluding the transition elements in terms of trend in oxidation states. D. There is no observable trend. © 2012 Pearson Education, Inc. Periodic Properties of the Elements A. B. C. D. There is no correlation between ionization energy and metallic character. Increasing ionization energy correlates with decreasing metallic character. Increasing ionization energy correlates with increasing metallic character. Decreasing ionization energy correlates with decreasing metallic character. © 2012 Pearson Education, Inc. Periodic Properties of the Elements Metals • Compounds formed between metals and nonmetals tend to be ionic. • Metal oxides tend to be basic. © 2012 Pearson Education, Inc. Periodic Properties of the Elements 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. © 2012 Pearson Education, Inc. Periodic Properties of the Elements Nonmetals • Nonmetals are dull, brittle substances that are poor conductors of heat and electricity. • They tend to gain electrons in reactions with metals to acquire a noble-gas configuration. © 2012 Pearson Education, Inc. Periodic Properties of the Elements Nonmetals • Substances containing only nonmetals are molecular compounds. • Most nonmetal oxides are acidic. © 2012 Pearson Education, Inc. Periodic Properties of the Elements A. B. C. D. Molecular and A is Sc. Molecular and A is P. Ionic and A is P. Ionic and A is Sc. © 2012 Pearson Education, Inc. Periodic Properties of the Elements 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. © 2012 Pearson Education, Inc. Periodic Properties of the Elements Metalloids • Metalloids have some characteristics of metals and some of nonmetals. • For instance, silicon looks shiny, but is brittle and a fairly poor conductor. © 2012 Pearson Education, Inc. Periodic Properties of the Elements Group Trends © 2012 Pearson Education, Inc. Periodic Properties of the Elements Alkali Metals • Alkali metals are soft, metallic solids. • The name comes from the Arabic word for ashes. © 2012 Pearson Education, Inc. Periodic Properties of the Elements Alkali Metals • They are found only in compounds in nature, not in their elemental forms. • They have low densities and melting points. • They also have low ionization energies. © 2012 Pearson Education, Inc. Periodic Properties of the Elements Alkali Metals Their reactions with water are famously exothermic. © 2012 Pearson Education, Inc. Periodic Properties of the Elements Alkali Metals • Alkali metals (except Li) react with oxygen to form peroxides. • K, Rb, and Cs also form superoxides: K + O2 KO2 • They produce bright colors when placed in a flame. © 2012 Pearson Education, Inc. Periodic Properties of the Elements A. B. C. D. © 2012 Pearson Education, Inc. Red Yellow Lilac Green Periodic Properties of the Elements A. B. C. D. Cs has the lowest ionization energy of the alkali metals. Cs has the greatest density of the alkali metals. Cs is the most conductive of the alkali metals. Cs has the most electrons of the alkali metals. © 2012 Pearson Education, Inc. Periodic Properties of the Elements Sample Exercise 7.10 Reactions of an Alkali Metal Write a balanced equation for the reaction of cesium metal with (a) Cl2(g), (b) H2O(l), (c) H2(g). © 2012 Pearson Education, Inc. Periodic Properties of the Elements Alkaline Earth Metals • Alkaline earth metals have higher densities and melting points than alkali metals. • Their ionization energies are low, but not as low as those of alkali metals. © 2012 Pearson Education, Inc. Periodic Properties of the Elements Alkaline Earth Metals • Beryllium does not react with water, and magnesium reacts only with steam, but the other alkaline earth metals react readily with water. • Reactivity tends to increase as you go down the group. © 2012 Pearson Education, Inc. Periodic Properties of the Elements A. B. C. D. CaCO3 is a very poor source of calcium due to its poor solubility in water. The dissolution reaction of metal carbonates is catalyzed by enzymes in the intestines. Metal carbonates are soluble in the acidic environment of the stomach. Metal carbonate solids can be directly passed into the skeletal Periodic system from the stomach. Properties © 2012 Pearson Education, Inc. of the Elements Group 6A • Oxygen, sulfur, and selenium are nonmetals. • Tellurium is a metalloid. Periodic • The radioactive polonium is a metal. © 2012 Pearson Education, Inc. Properties of the Elements A. B. C. D. 400 nm is highest wavelength of visible light and corresponds to the the lowest energy to break bonds. Assume it is minimal energy required to break O—O bonds and calculate. 400 nm is lowest wavelength of visible light and corresponds to the the lowest energy to break bonds. Assume it is minimal energy required to break O—O bonds and calculate. 750 nm is lowest wavelength of visible light and corresponds to the the lowest energy to break bonds. Assume it is minimal energy required to break O—O bonds and calculate. 750 nm is highest wavelength of visible light and corresponds to the the lowest energy to break bonds. Assume it is minimal energy Periodic required to break O—O bonds and calculate. Properties © 2012 Pearson Education, Inc. of the Elements Sulfur • Sulfur is a weaker oxidizer than oxygen. • The most stable allotrope is S8, a ringed molecule. © 2012 Pearson Education, Inc. Periodic Properties of the Elements Group VIIA: Halogens • The halogens are prototypical nonmetals. • The name comes from the Greek words halos and gennao: “salt formers.” © 2012 Pearson Education, Inc. Periodic Properties of the Elements A. B. C. D. Halogens are larger atoms than S and Se and would form an unstable, crowded X8 structure.. Halogens have the valence configuration ns2np6 and only need to share one pair of electrons to form a stable bond. Halogens with 7 valence electrons prefer to form X7 compounds. Halogens with np6 outer orbitals prefer to form X6 compounds. © 2012 Pearson Education, Inc. Periodic Properties of the Elements Group VIIA: Halogens • They have large, negative electron affinities. – Therefore, they tend to oxidize other elements easily. • They react directly with metals to form metal halides. • Chlorine is added to water supplies to serve as a disinfectant. © 2012 Pearson Education, Inc. Periodic Properties of the Elements Group VIIIA: Noble Gases • The noble gases have astronomical ionization energies. • Their electron affinities are positive. – Therefore, they are relatively unreactive. • They are found as monatomic gases. © 2012 Pearson Education, Inc. Periodic Properties of the Elements A. It is not possible to use the data in Table 7.7 to determine the characteristics of astatine. B. Yes, by extrapolating from the other data, we can estimate that the atomic radius is approximately 1.10 angstroms and I1 must be approximately 1000 kJ/mol. C. Yes, by extrapolating from the other data, we can estimate that the Periodic Properties atomic radius is approximately 1.5 angstroms and I1 must be of the approximately 900 kJ/mol. © 2012 Pearson Education, Inc. Elements