[Physics] electric charges of metals in electrostatics

Question

In electrostatics does metal gain electrons to be an ion or it conduct electrons in form of gaining them to have a negative electric charge

Answer 1

If you are asking about what happens to the electrons in a metal when placed in an electrostatic field, the simple answer is they get attracted to the end of the metal closes to the 'positive' side of the electric field, leaving an excess of 'positive' charge on the other side, the net effect of which is to 'cancel' out the applied electric field within the metal. That is, the mobile charge carriers (electrons) redistribute themselves on the surface of the metal so that there is no electric field within the metal itself (apart perhaps for a very thin layer on the surface).

The atoms in the metal do not generally become 'ionised' by the applied electric field, unless perhaps the metal becomes very very hot (beyond melting point, to become an ionised gas or plasma).

You may be getting confused with solid ionic compounds (metal oxides) which generally form on the surface of metals when exposed to atmospheric water and oxygen.

In that case, you its important to realise that metals do not generally 'gain' electrons to become ions. Rather, they typically 'lose' electrons during 'oxidation' to become positively charged ions (cations). The oxidation of a metal is generally referred to as 'corrosion', which in the case of iron or steel, results in the formation of 'rust'.

When a metal such as iron $\mathrm{Fe}$ comes in contact with salty water 'electrolyte' in the presence of oxygen, the following 'half-reactions' occur:

'Oxidation' of iron at at the metal-electrolyte interface known as the 'anode':

$$\mathrm{Fe(s)\rightarrow Fe^{2+}(aq) + 2\,e^-}$$

'Reduction' of oxygen at the metal-electrolyte interface known as the 'cathode':

$$\mathrm{O_2(g) + 2H_2O + 4\,e^- \rightarrow 4\,OH^-(aq)}$$

The iron(II) ions react with the hydroxide ions to form a precipitate of 'ferrous hydroxide':

$$\mathrm{Fe^{2+}(aq) + 2\,OH^-(aq) \rightarrow Fe(OH)_2(s)}$$

Which, when 'dehydrated' in the presence of oxygen, leaves behind the the familiar red/brown flaky porous ferric oxide or 'rust':

$$\mathrm{4\,Fe(OH)_2 + O_2 \rightarrow 2\,Fe_2O_3 · H_2O + 2\,H_2O}$$

In this case, the ferric oxide 'rust' which forms on the surface of the corroded metal is not generally as electrically conductive as the metal itself, since the iron is in ionic form and no longer has 'free' electrons to participate in conduction of electricity.