Metallic bonding: positive ions in a sea of electrons

A sodium atom has one lonely outer electron: $1\text{s}^2\,2\text{s}^2\,2\text{p}^6\,3\text{s}^1$.

In solid sodium, every atom lets go of that 3s electron. It isn't handed to a partner; it is released into the whole lump of metal.

What's left behind:

• a regular lattice of positive $\text{Na}^{+}$ ions;
• a "sea" of delocalised electrons, one per atom, free to move through the whole structure.

• Delocalised: not tied to one atom or one bond. Each electron belongs to the whole lattice.
• Positive ions, not atoms: the metal particles have lost their outer electrons.
• Only the outer (valence) electrons are delocalised. Inner shells stay put.
• There are no negative ions in a metal. The only negative particles are the electrons.