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| − | The traditional picture of the '''metallic bond''' was developed soon after the discovery of the electron. In this picture the valence [[electron]]s were viewed as an electron-gas permeating the [[crystal lattice]] structre of the metal atoms. The cohesive forces holding the metal together could be qualitatively seen as resulting from the [[electrostatic]] interaction of the positively charged metal atom cores with the negatively charged electron-gas.
| + | #REDIRECT [[Chemical bond]] |
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| − | With the development of [[quantum mechanics]] this picture has changed significantly. Quantum mechanically [[Covalent bond|covalent bonding]] can be described by constructing [[Molecular orbital theory|molecular orbitals]] from a linear combination of atomic orbitals ([[LCAO theory]]). For some molecules, such as benzene, which contain [[resonance]] in an extended [[conjugation|conjugated]] system, some of the molecular orbitals are delocalized and the electrons not fixed between particular atoms. Applying these concepts to metals leads to the Band theory of solids. In this theory the metallic bond is similar to the delocalized molecular orbitals of benzene, but on a much larger scale and with the bonding spread throughout the metal.
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| − | Let us consider a [[sodium]] atom. It has one valence electron in an s [[orbital]]. When we add another atom the overlap of the two s orbitals results in two molecular orbitals of differing energies. Adding a third atom results in three molecular orbitals and so on. In a small lump of sodium there are many thousands of atoms and consequently many thousands of molecular orbitals whose energies lie close together, This results in an energy band populated by the available electrons that is called the s-band. Similarly, with other atoms, you can also get a p-band from the overlap of atomic p orbitals.
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| − | In [[semiconductors]] there is a significant energy difference between different bands called a band gap. This is what gives semiconductors their usefull properties exploited in electronic circuits.
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| − | Back to [[Chemical bond]]
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| − | {{BranchesofChemistry}}
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| − | [[Category:Physical sciences]]
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| − | [[Category:Chemistry]]
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