The electron sea model treats metals as positive ion cores immersed in a delocalised "sea" of valence electrons. This explains metallic properties: electrical conductivity (free electrons carry current), thermal conductivity (electrons transfer kinetic energy), malleability/ductility (layers can slide without breaking bonds because the electron sea adjusts), and metallic lustre (free electrons absorb and re-emit light of all wavelengths). Metallic bond strength increases with number of valence electrons and decreasing atomic radius. Hence, transition metals (many valence electrons, smaller radii) typically have higher melting points than s-block metals. Na (mp 98 C) < Mg (650 C) < Al (660 C) reflects increasing valence electrons (1, 2, 3).