Lecture Presentation Chapter 7 Periodic Properties of the Elements 2012 Pearson Education Inc John D Bookstaver St Charles Community College Cottleville MO 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 2012 Pearson Education Inc 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 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 Periodic Properties of the Elements 2012 Pearson Education 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 number of inner electrons Periodic Properties of the Elements 2012 Pearson Education Inc 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 Periodic Properties of the Elements 2012 Pearson Education Inc Sizes of Ions Ionic size depends upon The nuclear charge The number of electrons The orbitals in which electrons reside 2012 Pearson Education Inc Periodic Properties of the Elements Sizes of Ions Cations are smaller than their parent atoms The outermost electron is removed and repulsions between electrons are reduced 2012 Pearson Education Inc Periodic Properties of the Elements Sizes of Ions Anions are larger than their parent atoms Electrons are added and repulsions between electrons are increased 2012 Pearson Education Inc 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 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 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 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 2012 Pearson Education 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 2012 Pearson Education Inc Periodic Properties of the Elements Trends in First Ionization Energies 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 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 2012 Pearson Education Inc Periodic Properties of the Elements Trends in Electron Affinity 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 Periodic Properties of the Elements 2012 Pearson Education Inc 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 Periodic Properties of the Elements 2012 Pearson Education Inc Properties of Metal Nonmetals and Metalloids 2012 Pearson Education Inc Periodic Properties of the 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 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 Nonmetals Nonmetals are dull brittle substances that