Question

How do the electronic structures of the atoms of a metallic element change when they react?

Answer 1

We know that a metallic bond is a bond that holds many metal atoms together in a metallic structure. The electrons from the outermost shell of the atom (valence electrons) get detached from the atom and start flowing in the sea of electrons together with the other electrons from the other metal atoms in the structure.

Complete answer:
As stated above, metals consist of sea electrons. These electrons are the valence electrons of all the metal atoms that are loosely bound to the metal atom and thus can be easily removed from the valence shell of the atom. These electrons move in a sea of free electrons and do not get attached to any specific atom. The attraction between this sea of electrons and the metal atoms are known as metallic bonding.
The hardness of the metal is because of the metallic bonding. Metals can conduct heat and can expand or contract on the application of heat. Free electrons can absorb the light falling on them and thus making the metal surface opaque looking. The electrons present at the surface of metals bounce the light falling on them with the same frequency.
And oxidation involves the LOSS of the valence electrons, cf.
$Ca\to C{{a}^{2+}}+2{{e}^{-}}~$ or $Fe\to F{{e}^{2+}}+2{{e}^{-}}$ or $Fe\to F{{e}^{3+}}+3{{e}^{-}}$
And for every oxidation reaction, there is a corresponding reduction reaction, usually of dioxygen to give the metal oxide, i.e. for iron to give rusts.

Note:
Remember that some of the properties of metal due to metallic bonding are: Metals are good conductors of electricity. This is because when an electric current is applied across the ends of metal, this sea of electrons starts flowing in a specific uniform direction, and hence the current can flow through metal.