What part of an element determines whether it is a metal or not?

Chemical reactivity and bonding is all to do with the electrons and their configuration about the nucleus. Here is a recent answer I gave to a previous question on the topic. I don't recall if it was voted on (too complicated?).

Why there are more metals than nonmetals?

You need about two years worth of wave mechanics to grasp it so I won’t try and give you details.

Bonding in metals is characterized by bands of bonding molecular orbitals that are only partially filled and which extend throughout the lattice. Overlap of N (N = 6 × 10^23 ?) AOs yields N closely-spaced MOs half of which span bonding energies and half that span nonbonding energies. At the Fermi level (at the bonding and antibonding switchover) there are free e⁻s that can conduct heat and electricity, and scatter visible light to give metallic lustre. The requirement to form bands is that there usually eight or more atoms in the coordination sphere; most metals are close packed with 12:12 coordination. There must also be atomic orbitals that are partially filled or near enough in energy to form an unfilled band that overlaps with the filled band. Examples: Li is bcc: 8:8 coordination; the 2s AOs are sufficiently extended to overlap to form the 2s band (doesn’t happen in H 1s not extended sufficiently); Mg [Ne]3s^2 ; 3p band overlaps with initially filled 3s band hence it is a metal. C ([He] 2s^2 2^p2; no empty AOs suitable for bonding): atom only 4 coordinate (small) so band is filled, non-metal covalent lattice. As we go down the PT the atoms get larger (favouring band formation) but more importantly AOs become available to form bands (Prof Schrodinger and his Wave Equation explains it “all”). The TM elements are all metals because they have partly filled d and f AOs plus s AOs and p AOs that can also join in the band. :)

So metals are formed by elements to left of PT: large size (high coordination numbers), AOs suitable for overlap into bands. Going down PT size increases and more AOs are available for band formation, hence more metals. The upper RHS atoms are too small, the AOs are filled or not suitable in energy to form bands so localized covalent bonding is energetically favoured. (As I recall, Iodine under about a million atmospheres flips to a metallic lattice: easily determined by putting an X-ray beam through it.)

The number of proton -- THUS the number of electrons. The number of electrons in turn determines its number of valence electrons, and thus its chemical properties, and therefore if it is a metal or what.

it's components? what it's made of?

JC probably has it right.. and it's close to my answer x) lol