ProblemSet1 - Solutions

ProblemSet1 - Solutions - Solutions Problem Set#1 2011 1.1...

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1) For each of the following groups of metals, name at least two physical proper- ties that are commonly associated with each group and distinguish it from the other metals. Provide a qualitative explanation for those characteristics in terms of structure and bonding. a) Alkali and alkali earth metals • Characteristic properties - Highly reactive - Low melting temperature - Low density - Very soft • The alkali and alkali earth atoms have 1 or 2 electrons, respectively, which are weakly bonded to the atom. The low ionization energy of these elements re- sults in them being highly reactive. In the metal, the electrons become easily delocalized. The large atomic radius results in a low density. The weak, non- directional metallic bonds lead to a low melting temperature and low hard- ness. b) Transition metals • Characteristic properties - High melting point - Hard - High conductivity - Several oxidation states - Characteristic colors • The d electron orbitals are partially occupied in the transition metals and con- tribute to the bonding. The d electron states are quite localized and have di- rectional character. As a consequence of the large number of valence elec- trons participating in the bonding, the bonding is very strong resulting in a high melting point and a high mechanical hardness. • The high density of states of the d electrons leads to a high conductivity. • Transition metals can form compounds in various oxidation states, due to the relatively low reactivity of unpaired d electrons. Solutions Problem Set #1, 2011 1.1
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• The characteristic colors of transition metal compounds are caused by transi- tions between the d- electron states. c) Refractory metals • Characteristic properties - Very hard - High melting point - Oxidation resistant • The nearly half-Flled d -electron shell of these metals is near the optimum for maximum bond strength. The results in the very high melting temperature and hardness. • After the noble metals, these metals are the most corrosion resistant metals.
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ProblemSet1 - Solutions - Solutions Problem Set#1 2011 1.1...

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