Chapter 7 - Periodic Properties of the Elements

Chapter 7 - Periodic Properties of the Elements - 1 Chapter...

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Unformatted text preview: 1 Chapter 7 Chapter 7 Periodic Properties of the Elements Periodic Properties of the Elements Development of Periodic Table Development of Periodic Table Elements in the same group generally have similar chemical properties. Properties are not identical, however. 2 Development of Periodic Table Development of Periodic Table Dmitri Mendeleev and Lothar Meyer (~1869) independently came to the same conclusion about how elements should be grouped in the periodic table . Henry Moseley (1913) developed the concept of atomic numbers (the number of protons in the nucleus of an atom) Development of Periodic Table 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. 3 Periodic Trends Periodic Trends In this chapter, we will rationalize observed trends in Sizes of atoms and ions Ionization energy Electron affinity Effective Nuclear Charge 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. 4 Effective Nuclear Charge Effective Nuclear Charge EffectiveNuclearCharge.mov The effective nuclear charge, Z eff , is: Z eff = Z S where Z is the atomic number and S is a screening constant, usually close to the number of inner electrons. Z eff is a representation of the average electrical field experienced by a single electron. Sizes of Atoms Sizes of Atoms The bonding atomic radius is defined as one-half of the distance between covalently bonded nuclei. 5 Sizes of Atoms 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 Sizes of Ions Sizes of Ions Ionic size depends upon: Nuclear charge....
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Chapter 7 - Periodic Properties of the Elements - 1 Chapter...

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