system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why is a metal a metal?
gpt
If you zoom into a metal atom, you will see that it has "shells" in which its electrons can orbit. It's outer shell is called the valence shell, and the number of valence electrons that orbit in this shell depend on the atom.

Metals are made up of numerous metal atoms, such as copper or iron, that share their valence electrons between them in order to fill their valence shell. These valence electrons can move freely between the atoms making sure that each atom has a full shell. If a voltage is applied to the metal, a current will flow as the electrons can move freely around.

The freely moving electrons also allow the metal atoms to be easily moved without breaking the bonds between the atoms. This allows metals to be malleable and ductile.