Chemistry The Central Science 11 th edition Theodore

Chemistry, The Central Science, 11 th edition Theodore L. Brown; H. Eugene Le. May, Jr. ; and Bruce E. Bursten Chapter 7 Periodic Properties of the Elements John D. Bookstaver St. Charles Community College Cottleville, MO Periodic Properties of the Elements © 2009, Prentice-Hall, Inc.

Aim: What is effective nuclear charge? Do Now: What does n represent for atoms? Periodic Properties of the Elements © 2009, Prentice-Hall, Inc.

Development of Periodic Table • Elements in the same group generally have similar chemical properties. • Physical properties are not necessarily similar, however. Periodic Properties of the Elements © 2009, Prentice-Hall, Inc.

Development of Periodic Table Dmitri Mendeleev and Lothar Meyer independently came to the same conclusion about how elements should be grouped. Periodic Properties of the Elements © 2009, Prentice-Hall, Inc.

Development of Periodic Table Mendeleev, for instance, predicted the discovery of germanium (which he called ekasilicon) as an element with an atomic weight between that of zinc and arsenic, but with chemical properties similar to those of silicon. Periodic Properties of the Elements © 2009, Prentice-Hall, Inc.

Periodic Trends • In this chapter, we will rationalize observed trends in – Sizes of atoms and ions. – Ionization energy. – Electron affinity. Periodic Properties of the Elements © 2009, Prentice-Hall, Inc.

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. Periodic Properties of the Elements © 2009, Prentice-Hall, Inc.

Effective Nuclear Charge 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 Periodic number of inner Properties of the electrons. Elements © 2009, Prentice-Hall, Inc.

Coulomb’s Law Coulomb's law states that: The magnitude of the electrostatic force of attraction between two point charges is directly proportional to the product of the magnitudes of charges and inversely proportional to the square of the distance between them. The force is along the Periodic Properties straight line joining them. of the Elements © 2009, Prentice-Hall, Inc.

What Is the Size of an Atom? The bonding atomic radius is defined as one-half of the distance between covalently bonded nuclei. Periodic Properties of the Elements © 2009, Prentice-Hall, Inc.

Example Use effective nuclear charge and Coulomb’s Law to order the relative sizes of sodium, magnesium, and aluminum. Explain your reasoning. Periodic Properties of the Elements © 2009, Prentice-Hall, Inc.

Sizes of Atoms 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 increasing value of n). Periodic Properties of the Elements © 2009, Prentice-Hall, Inc.

Sample Exercise 7. 2 Pg. 265 Referring to the periodic table, arrange (as much as possible) the atoms, B, C, Al, and Si in order of increasing size. Periodic Properties of the Elements © 2009, Prentice-Hall, Inc.

Aim: What are the periodic trends in ionic radius, and ionization energy? Do Now: How do metals and non metals tend to make ions? Periodic Properties of the Elements © 2009, Prentice-Hall, Inc.

Sizes of Ions • Ionic size depends upon: – The nuclear charge. – The number of electrons. – The orbitals in which electrons reside. Periodic Properties of the Elements © 2009, Prentice-Hall, Inc.

Sizes of Ions • Cations are smaller than their parent atoms. – The outermost electron is removed and repulsions between electrons are reduced. Periodic Properties of the Elements © 2009, Prentice-Hall, Inc.

Sizes of Ions • Anions are larger than their parent atoms. – Electrons are added and repulsions between electrons are increased. Periodic Properties of the Elements © 2009, Prentice-Hall, Inc.

Sizes of Ions • Ions increase in size as you go down a column. – This is due to increasing value of n. Periodic Properties of the Elements © 2009, Prentice-Hall, Inc.

Sizes of Ions • In an isoelectronic series, ions have the same number of electrons. • Ionic size decreases with an increasing nuclear charge. Periodic Properties of the Elements © 2009, Prentice-Hall, Inc.

Sample Exercise 7. 3 Pg. 265 Arrange Mg 2+, Ca 2+, and Ca in order of decreasing radius. Periodic Properties of the Elements © 2009, Prentice-Hall, Inc.

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. Periodic Properties of the Elements © 2009, Prentice-Hall, Inc.

Think Critically What would you expect to see from one ionization energy to the next in terms of energy required? Why? I 1 I 2 I 3 Ix Periodic Properties of the Elements © 2009, Prentice-Hall, Inc.

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. Periodic Properties of the Elements © 2009, Prentice-Hall, Inc.

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. Periodic Properties of the Elements © 2009, Prentice-Hall, Inc.

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. Periodic Properties of the Elements © 2009, Prentice-Hall, Inc.

Trends in First Ionization Energies However, there are two apparent discontinuities in this trend. Periodic Properties of the Elements © 2009, Prentice-Hall, Inc.

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. Periodic Properties of the Elements © 2009, Prentice-Hall, Inc.

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. Periodic Properties of the Elements © 2009, Prentice-Hall, Inc.

Sample Exercise 7. 4 Pg. 267 Arrange the ions K+, Cl-, Ca 2+, and S 2 - in order of decreasing size. Periodic Properties of the Elements © 2009, Prentice-Hall, Inc.

Electron Configurations of Ions • When writing the electron configuration of an ion, electrons are always removed from the occupied orbitals having the highest principal quantum number, n. If more than one occupied subshell for an n occurs, we take from the highest value of l. • Ex: Fe: [Ar] 4 s 23 d 6 --> Fe 2+ : [Ar]3 d 6 + 2 e. Periodic Properties of the Elements © 2009, Prentice-Hall, Inc.

Practice Using the electron configuration of Sn, write the electron configurations for Sn+2 and Sn+4 Periodic Properties of the Elements © 2009, Prentice-Hall, Inc.

Aim: What is electron affinity, and how is it different than ionization energy? Do Now: Which elements tend to have the lowest ionization energy? Why is ionization Periodic Properties energy positive? of the Elements © 2009, Prentice-Hall, Inc.

Electron Affinity Electron affinity is the energy change accompanying the addition of an electron to a gaseous atom: Cl + e− Cl− Periodic Properties of the Elements © 2009, Prentice-Hall, Inc.

Trends in Electron Affinity In general, electron affinity becomes more exothermic as you go from left to right across a row. Periodic Properties of the Elements © 2009, Prentice-Hall, Inc.

Trends in Electron Affinity There again, however, two discontinuities in this trend. Periodic Properties of the Elements © 2009, Prentice-Hall, Inc.

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. Periodic Properties of the Elements © 2009, Prentice-Hall, Inc.

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 Periodic repulsion. Properties of the Elements © 2009, Prentice-Hall, Inc.

In General • The greater the attraction between an atom and an added electron, the more negative the atom’s electron affinity. • Ionization energies are positive, as energy must be absorbed to take away an electron. • However, electron affinity is a negative value Periodic Properties of the Elements © 2009, Prentice-Hall, Inc.

Properties of Metal, Nonmetals, and Metalloids Periodic Properties of the Elements © 2009, Prentice-Hall, Inc.

Metals versus Nonmetals Differences between metals and nonmetals tend to revolve around these properties. Periodic Properties of the Elements © 2009, Prentice-Hall, Inc.

Metals versus Nonmetals • Metals tend to form cations. • Nonmetals tend to form anions. Periodic Properties of the Elements © 2009, Prentice-Hall, Inc.

Metals They tend to be lustrous, malleable, ductile, and good conductors of heat and electricity. Periodic Properties of the Elements © 2009, Prentice-Hall, Inc.

Metals • Compounds formed between metals and nonmetals tend to be ionic. • Metal oxides tend to be basic. – When dissolved in water they form hydroxides (bases) – Na 2 O (s) + H 2 O(l) – 2 Na. OH(aq) Periodic Properties of the Elements © 2009, Prentice-Hall, Inc.

Sample Exercise 7. 8 Pg. 276 a) Would you expect Scandium oxide to be a solid, liquid, or gas at room temperature? b) Write a balanced chemical equation for the reaction of scandium oxide with nitric acid. Periodic Properties of the Elements © 2009, Prentice-Hall, Inc.

Nonmetals • These 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. Periodic Properties of the Elements © 2009, Prentice-Hall, Inc.

Nonmetals • Substances containing only nonmetals are molecular compounds. • Most nonmetal oxides are acidic. – When dissolved in water they form acids – CO 2(s) + H 2 O (l) – H 2 CO 3(aq) Periodic Properties of the Elements © 2009, Prentice-Hall, Inc.

Sample Exercise 7. 9 Pg. 277 Write a balanced equation for the reaction of solid selenium dioxide, Se. O 2(s), with a) Water b) Aqueous sodium hydroxide Periodic Properties of the Elements © 2009, Prentice-Hall, Inc.

Metalloids • These have some characteristics of metals and some of nonmetals. • For instance, silicon looks shiny, but is brittle and fairly poor conductor. Periodic Properties of the Elements © 2009, Prentice-Hall, Inc.

Aim: What are the trends of Group 1 and 2 Metals, and selected Nonmetals Do Now: What happens when Alkali Metals react with H 2 O (l)? Is a gas formed? If so, what gas is formed? Periodic Properties of the Elements © 2009, Prentice-Hall, Inc.

Group Trends Periodic Properties of the Elements © 2009, Prentice-Hall, Inc.

Alkali Metals • Alkali metals are soft, metallic solids. • The name comes from the Arabic word for ashes. Periodic Properties of the Elements © 2009, Prentice-Hall, Inc.

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. Periodic Properties of the Elements © 2009, Prentice-Hall, Inc.

Alkali Metals Their reactions with water are famously exothermic. Periodic Properties of the Elements © 2009, Prentice-Hall, Inc.

Alkali Metals • Alkali metals (except Li) react with oxygen to form peroxides. • K, Rb, and Cs also form superoxides: K + O 2 KO 2 • They produce bright colors when placed in a flame. Periodic Properties of the Elements © 2009, Prentice-Hall, Inc.

Sample Exercise 7. 10 Pg 280 Write a balanced equation for the reaction of cesium metal with a) Cl 2 b) H 2 O (l) c) H 2 (g) Periodic Properties of the Elements © 2009, Prentice-Hall, Inc.

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. Periodic Properties of the Elements © 2009, Prentice-Hall, Inc.

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. Periodic Properties of the Elements © 2009, Prentice-Hall, Inc.

Group 6 A • Oxygen, sulfur, and selenium are nonmetals. • Tellurium is a metalloid. • The radioactive polonium is a metal. Periodic Properties of the Elements © 2009, Prentice-Hall, Inc.

Oxygen • There are two allotropes of oxygen: – O 2 – O 3, ozone • There can be three anions: – O 2−, oxide – O 22−, peroxide – O 21−, superoxide • It tends to take electrons from other elements (oxidation). Periodic Properties of the Elements © 2009, Prentice-Hall, Inc.

Sulfur • Sulfur is a weaker oxidizer than oxygen. • The most stable allotrope is S 8, a ringed molecule. Periodic Properties of the Elements © 2009, Prentice-Hall, Inc.

Group VIIA: Halogens • The halogens are prototypical nonmetals. • The name comes from the Greek words halos and gennao: “salt formers”. Periodic Properties of the Elements © 2009, Prentice-Hall, Inc.

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 Periodic Properties of the Elements © 2009, Prentice-Hall, Inc.

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. Periodic Properties of the Elements © 2009, Prentice-Hall, Inc.

Group VIIIA: Noble Gases • Xe forms three compounds: – Xe. F 2 – Xe. F 4 (at right) – Xe. F 6 • Kr forms only one stable compound: – Kr. F 2 • The unstable HAr. F was synthesized in 2000. Only stable at low temp. Periodic Properties of the Elements © 2009, Prentice-Hall, Inc.

Practice Exercise Questions: • Answer the following in your notebook in full sentences 7. 67 a)Why is calcium generally more reactive than magnesium 7. 71 a) As described in Section 7. 7, the alkali metals react with hydrogen to form hydrides and react with halogens to form halides. Compare the roles of hydrogen and halogens in these reactions? How are the forms of hydrogen and halogens in the products alike? Periodic Properties of the Elements © 2009, Prentice-Hall, Inc.