Chapter 8: Periodic Relationships Among the Elements PDF

Chapter 8: Periodic Relationships Among the Elements  Development of Periodic Table Elements in the same group generally have similar chemical properties. Physical properties are not necessarily similar, however. © 2009, Prentice-Hall, Inc. Development...

Chapter 8: Periodic Relationships Among the Elements  Development of Periodic Table Elements in the same group generally have similar chemical properties. Physical properties are not necessarily similar, however. © 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. © 2009, Prentice-Hall, Inc.  Periodic Trends In this chapter, we will rationalize observed trends in – Effective nuclear charge – Sizes of atoms and ions. – Ionization energy. – Electron affinity. – Metallic Character © 2009, Prentice-Hall, Inc. Structure of the atom  Effective Nuclear Charge (Zeff) 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. Zeff Increses from left to right and bottom to top © 2009, Prentice-Hall, Inc.  Atomic radius tends to: - increase from right to left across a row (due to decreasing Zeff). - increase from top to bottom of a column (due to increasing value of n). Sizes of Ions 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.  Sizes of Ions In an isoelectronic series, ions have the same number of electrons. Ionic size decreases with an increasing nuclear charge. © 2009, Prentice-Hall, Inc.  Bond Length - Bond length is defined by the distance between the two nuclei. - The larger the radius, the longer the distance (bond length) © 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. © 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. © 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. © 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. © 2009, Prentice-Hall, Inc.  Ionization Energy - Removing second electron is harder than first electron; requires more energy (I1