Click here to buy a book, photographic periodic table poster, card deck, or 3D print based on the images you see here! Common Properties Abundance in Earth's Crust. 27 Co. Available cobalt properties More properties Cobalt is a brittle, hard, silver-grey transition metal with magnetic properties similar to those of iron (it is ferromagnetic). It has a high melting point and is hard-wearing even at high temperatures. Cobalt - Cobaltum [Co] Group: 9 Period: 4 Atomic number: 27 Atomic mass: Configuration: [Ar] 3d 7 4s 2 Atomic radius: pm Covalent radius: pm Electron affinity: eV Ionization energy: eV Electronic term: 4 F 9/2 Mass fraction in the earth crust: Mass fraction in the earth space: Electronegativity.