A metal is characterized by its lustre, the ease with which it may be deformed rather than shattered by hammering, and its high electrical and thermal conductivities. Metals also tend to have higher densities than other types of solid. The starting point for theories of the structures of metals is to regard them as consisting of cations of the metal atoms embedded in a sea formed by the discarded valence electrons.
The mobility of these electrons accounts for the mechanical, optical, and electrical properties of metals.
Properties of solids
The spherical cations can pack closely together yet still give rise to locally neutral electrical assemblies. This is because of the ability of the electrons to spread between the cations and neutralize their charges regardless of how closely they are packed. The closeness of the packing of the atoms accounts for the high densities of metals.
In the context of theories of the chemical bond, a metal is one extremely large homonuclear molecule. For an alternative point of view, see crystal.
If a sample of sodium metal is thought of as consisting of n sodium atoms where each atom has a 3 s orbital for use in the construction of molecular orbitals and each atom supplies one electron to a common pool, then from these n atomic orbitals n molecular orbitals can be constructed. Each orbital has a characteristic energy, and the range of energies spanned by the n orbitals is finite, however great the value of n.
If n is very large, it follows that the energy separation between neighbouring molecular orbitals is very small and approaches zero as n approaches infinity. The molecular orbitals then form a band of energies. Another similar band can be formed by the overlap of the 3 p orbitals of the atoms, but there is a substantial band gap —i.
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Sign up to take part. A Nature Research Journal. A QUESTION of fundamental importance in the theory of the solid state is the nature of the arrangement of the ultimate particles in amorphous or vitreous bodies, of which glass is the most familiar example. Is it to be supposed that the molecules are packed together at more or less uniform distances apart, as in crystals, the orientation of individual molecules or of groups of molecules being, however, arbitrary?
Or, on the other hand, is the spacing of the molecules itself irregular, the solid exhibiting in a more or less permanent form local fluctuations of density similar to those that arise transitorily in liquids owing to the movement of the molecules? The physical properties of amorphous solids, notably their softening and viscous flow below the temperature of complete fusion, would tend to support the latter view, but the possibility of a closer approximation to the crystalline state should not entirely be, ruled out, especially in view of the very interesting recent work of Lord Rayleigh on the feeble double refraction exhibited by fused silica Proc.
A good deal might be expected to depend on the nature of the material, its mode of preparation, and heat treatment. For the same reason these solids have relatively high coefficients of expansion. They melt at low temperatures and have low heat of fusion.
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The bonding within the molecules is covalent and strong whereas the forces which operate between different molecules of the crystal lattice are the weak van der Waals forces. As result of these weak forces, the molecular solids are soft and vaporize very readily.
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These solids do not conduct electricity. They are, therefore, unable to move from one moleculeto another on the application of electric field. Examples of these solids are iodine, sulphur, phosphorus non polar and water, sugar polar etc. Skip to main content.