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Transcript of Metals
together by metallic bonds. Metallic bonds
are the electrostatic force of attractions
between the positive ions and the
sea of electrons. Most metals are close packed that is they fit as many atoms as possible into the available volume. Each atom in the structure has twelve touching neighbours. Such a metal is described as 12-co-ordinated Some metals are packed less efficiently having only eight touching neighbours. They are 8-co-ordinated (mainly in group one of the periodic table. It would be misleading to suppose that all the atoms in a piece of metal are arranged in a regular way. Any piece of metal is made up of a large number of crystal grains which are regions of regularity. At the grain boundaries atoms have become misaligned. Physical properties Metals tend to have high melting and boiling points because of the strength of the metallic bond. The strength of the bond varies from metal to metal and depends on the number of the electrons which each atom delocalises into the sea of electrons and on the packing. Alkali metals like Na and K (,Rb,Cs) have low melting point because they only give 1 electron into the sea of electrons.
But metals like Al, Ga have high melting and boilig points because they give three electrons into the sea of electrons. Conduction Themal Metals are good conductors of heat. Heat energy is picked up by the electrons as additional kinetic energy. The energy is transferred throughout the rest of the metal by the moving electrons. Electrical Metals conduct electricity. The delocalised electrons are free to move throughout the structure in 3 dimensions. They can cross grain boundaries. Even though the pattern may be disrupted at the boundary, as long as atoms are touching each other, the metallic bond is still present.
Liquid metals also conduct electricity showing that the metal atoms may be free to move the delocalisation remians in force until the metal boils. Maleability Metals are described as maleable and ductile. This is because of the ability of the atoms to roll over each other into new positions without weakening the metallic bond.