Presentation on theme: "Chapter 7 Periodic Properties of the Elements. Development of Periodic Table Elements in the same group generally have similar chemical properties. Physical."— Presentation transcript:
Chapter 7 Periodic Properties of the Elements
Development of Periodic Table Elements in the same group generally have similar chemical properties. Physical properties are not necessarily similar, however.
Development of Periodic Table Dmitri Mendeleev and Lothar Meyer independently came to the same conclusion about how elements should be grouped.
Development of 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 Trends In this chapter, we will rationalize observed trends in –Sizes of atoms and ions. –Ionization energy. –Electron affinity.
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.
Effective Nuclear Charge The effective nuclear charge, Z eff, is found this Way: Z eff = Z S where Z is the atomic number and S is a screening constant, Usually close to the number of Inner electrons.
What Is the Size of an Atom? The bonding atomic radius is defined as one-half of the distance between covalently bonded nuclei.
Sizes of Atoms Bonding atomic radius tends to… …decrease from left to right across a row(due to increasing Z eff ). …increase from top to bottom of a column (due to increasing value of n).
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, CH 3 SH, whose structure is shown in the margin. Use Figure 7.7 to predict the lengths of the CS, CH, SH and bonds in this molecule. Using Figure 7.7, predict which will be greater, the PBr bond length in PBr 3 or the AsCl bond length in AsCl 3. Answer: PBr Using Figure 7.7, predict which will be greater, the PBr bond length in PBr 3 or the AsCl bond length in AsCl 3.
PBr Referring to a periodic table, arrange (as much as possible) the following atoms in order of increasing size: 15 P, 16 S, 33 As, 34 Se. (Atomic numbers are given for the elements to help you locate them quickly in the periodic table.) Arrange the following atoms in order of increasing atomic radius: 11 Na, 4 Be, 12 Mg.
Sizes of Ions Ionic size depends upon: –The nuclear charge. –The number of electrons. –The orbitals in which electrons reside.
Sizes of Ions Cations are smaller than their parent atoms. –The outermost electron is removed and repulsions between electrons are reduced.
Sizes of Ions Anions are larger than their parent atoms. –Electrons are added and repulsions between electrons are increased.
Sizes of Ions Ions increase in size as you go down a column. –This is due to increasing value of n.
Sizes of Ions In an isoelectronic series, ions have the same number of electrons. Ionic size decreases with an increasing nuclear charge.
Arrange these atoms and ions in order of decreasing size: Mg 2+, Ca 2+, and Ca. Which of the following atoms and ions is largest: S 2–, S, O 2– ? Arrange the Isoelectronic Series of ions K +, Cl –, Ca 2+, and S 2– in order of decreasing size. Which of the following ions is largest, Rb +, Sr 2+, or Y 3+ ?
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 first electron. –The second ionization energy is that energy required to remove second electron, etc.
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.
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, Z eff is essentially the same, but the valence electrons are farther from the nucleus.
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, Z eff increases.
Trends in First Ionization Energies However, there are two apparent discontinuities in this trend.
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 nucleus. –There is also a small amount of repulsion by the s electrons.
Trends in First Ionization Energies The second occurs between Groups VA and VIA. –The electron removed comes from doubly occupied orbital. –Repulsion from the other electron in the orbital aids in its removal.
Which will have the greater third ionization energy, Ca or S? Referring to a periodic table, arrange the following atoms in order of increasing first ionization energy: Ne, Na, P, Ar, K. Which has the lowest first ionization energy, B, Al, C, or Si? Which has the highest first ionization energy?
Write the electron configuration for (a) Ca 2+ (b) Co 3+, and (c) S 2–. Write the electron configuration for (a) Ga 3+, (b) Cr 3+, and (c) Br –.
Electron Affinity Electron affinity is the energy change accompanying the addition of an electron to a gaseous atom: Cl + e Cl
Trends in Electron Affinity There are again, however, two discontinuities in this trend.
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 nucleus and feels repulsion from the s-electrons.
Trends in Electron Affinity The second occurs between Groups IVA and VA. –Group VA has no empty orbitals. –The extra electron must go into an already occupied orbital, creating repulsion.
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.
Alkaline Earth Metals Beryllium does not react with water and magnesium reacts only with steam, but the others react readily with water. Reactivity tends to increase as you go down the group.
Group 6A Oxygen, sulfur, and selenium are nonmetals. Tellurium is a metalloid. The radioactive polonium is a metal.
Oxygen There are two allotropes of oxygen: –O2–O2 –O 3, ozone There can be three anions: –O 2, oxide –O 2 2, peroxide –O 2 1, superoxide It tends to take electrons from other elements (oxidation).
Sulfur Sulfur is a weaker oxidizer than oxygen. The most stable allotrope is S 8, a ringed molecule.
Group VIIA: Halogens The halogens are prototypical nonmetals. The name comes from the Greek words halos and gennao: salt formers.
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
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.
Group VIIIA: Noble Gases Xe forms three compounds: –XeF 2 –XeF 4 (at right) –XeF 6 Kr forms only one stable compound: –KrF 2 The unstable HArF was synthesized in 2000.
(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. (c) Write the balanced chemical equation for the reaction between copper(II) oxide and sulfuric acid.
Write the balanced chemical equation for the reaction of solid tetraphosphorus hex-oxide with water. Write the balanced chemical equations for the reactions of solid selenium dioxide with (a) water, (b) aqueous sodium hydroxide.
Write a balanced equation that predicts the reaction of cesium metal with (a) Cl 2 (g), (b) H 2 O(l), (c) H 2 (g). Write a balanced equation for the reaction between potassium metal and elemental sulfur.
Sample Integrative Exercise Putting Concepts Together The element bismuth (Bi, atomic number 83) is the heaviest member of group 5A. A salt of the element, bismuth subsalicylate, is the active ingredient in Pepto-Bismol®, an over-the-counter medication for gastric distress. (a) The covalent atomic radii of thallium (Tl) and lead (Pb) are 1.48 Å and 1.47 Å, respectively. Using these values and those in Figure 7.7, predict the covalent atomic radius of the element bismuth (Bi). Explain your answer. (b) What accounts for the general increase in atomic radius going down the group 5A elements? (c) Another major use of bismuth has been as an ingredient in low-melting metal alloys, such as those used in fire sprinkler systems and in typesetting. The element itself is a brittle white crystalline solid. How do these characteristics fit with the fact that bismuth is in the same periodic group with such nonmetallic elements as nitrogen and phosphorus? (d) Bi 2 O 3 is a basic oxide. Write a balanced chemical equation for its reaction with dilute nitric acid. If 6.77 g of Bi 2 O 3 is dissolved in dilute acidic solution to make 0.500 L of solution, what is the molarity of the solution of Bi 3+ ion? (e) 209 Bi is the heaviest stable isotope of any element. How many protons and neutrons are present in this nucleus? (f) The density of Bi at 25 °C is 9.808 g/cm 3. How many Bi atoms are present in a cube of the element that is 5.00 cm on each edge? How many moles of the element are present?