A metal atom is large, so the nucleus cannot attract and hold its outermost electrons. The metal loses those electrons and becomes positively charged kernels. The electrons then flow in the solid structure passing between these positive kernels.
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The more electrons a metal loses, the more its positive charge. A greater positive charge also means that the metal now has fewer electrons which its nucleus furiously tries to protect. It will pull the remaining outer electrons inwardly, shrinking the ionic size. These three factors - charge on the metal ion (kernel), size of the ion, and the number of valence electrons- affect the metallic bond's strength.
Such metal ions (kernels) with a high positive charge and small size will strongly attract the negative flowing electrons, and to break such an electrostatic bond will require high energy. High melting and boiling points of metals reflect the high energy required to break the metal structure.
For example, Na, Mg, and Al can lose one, two, and three valence electrons to form Na+, Mg+2, and Al+3 metal kernels. Since Al lost three electrons, it has the highest positive charge and smallest size. It will have the highest kernel-electron attractive power, in other words, the strongest attractive interaction. Therefore, compared to Na at 882.9 oC, Al will require a boiling temperature of 2470 oC to break the attractive interactions, destroying the crystal structure.
Element | Melting Point | Boiling point | Valence Electrons |
|---|---|---|---|
Sodium | 97.79 oC | 882.9 oC | 1 |
Aluminium | 660 oC | 2470 oC | 3 |
Related Reading- Metallic Bond
