[antwell]

Some questions on metallic bonds:

1. Why do the valence electrons of metals delocalise to form a sea of electrons? Why doesn't a sodium atom form a covalent bond with another sodium, for example, since this would allow it to fill up its 3s orbital (and thus become stable?)?

2. What determines how many valence electrons are delocalised per atom in metals? Why do some aluminium atoms delocalise 2 electrons, while others delocalise 3?

3. How does the coordination number of the metal affect the magnitude of attraction (or strength?) in the metallic bond? The greater the coordination number, the more electrons delocalised?

4. Am I right to say that the delocalised electrons in metals possess a large variety of energy levels, and hence are able to absorb and emit most of the photons which hit the metal? Why do the electrons possess a large variety of energy levels even though they move within the overlapping valence orbitals?

[Borek]

Remember: library first, wiki/google second, ask on forums third!

[xiankai]

1. subshell stability is not the same as quantum shell stability (aka octet rule). on the contrary, the mutual electron pair repulsion in the 3s subshell makes it unstable. plus since Na forms a pretty small cation, a covalent bond between two Na atoms would bring their positive nuclei together very close, another reason for instability.

2. delocalised electrons in a metallic bond will result in positive metal cations. here you have to find the oxidation states for the metal, which can give you a hint. aluminium atoms delocalise 2 electrons? i would be thinking of a statistical fluctuation, but honestly i don't know.

3. the greater the coordination number, the closer the atoms are packed together. it would be incorrect to say more electrons are delocalised, because each atom still gives up the same number of electrons. perhaps it would be more accurate if the metallic bond is stronger because of closer proximity between positive metal cations and negative electrons.

4. the question here is not how many energy levels electrons have, but what is the highest energy level electrons can reach. a low energy level electron may not be able to absorb a photon if it is too strongly attracted to the nucleus (unless a very high energy photon is used of course). likewise, a high energy level electron would be able to do so easily. as for whether electrons have a large variety of energy levels, that again depends on the metal since electron-nucleus attraction can vary greatly.