Sublimation energy is the heat required to change one mole of solid to gas.
I don't understand why metals have sublimation energy, the reason being that they are solid substances and even at very high temperatures, they exist as a liquid. How can there be a metal in gaseous form?
Sodium atoms have 11 electrons, one more than the extremely stable configuration of the noble gas neon. Because of this and its low first ionization energy of 495.8 kJ/mol, the sodium atom is much more likely to lose the last electron and acquire a positive charge than to gain one and acquire a negative charge. This process requires so little energy that sodium is readily oxidized by giving up its 11th electron. In contrast, the second ionization energy is very high (4562 kJ/mol), because the 10th electron is closer to the nucleus than the 11th electron. As a result, sodium usually forms ionic compoundsinvolving the Na+ cation.
The most common oxidation state for sodium is +1. It is generally less reactive than potassium and more reactive than lithium.Sodium metal is highly reducing, with the standard reduction potential for the Na+/Na couple being −2.71 volts,though potassium and lithium have even more negative potentials.
According to molecular orbital theory, disodium should be stable in the gas phase, with a bond order of one. The molecular orbital diagram is the same for all the alkali metals since they all have one valence electron in an ss orbital.