Atomic Number Symbol Atomic Radius (nm) Ionization Energy (kJ/mol) Melting Point (°C) Density (g/cm3) Electronegativity 1 H 0.032 1312 -259.2 0.090 2.20 2 He 0.031 2372 -272.2 0.1785 0.00 3 Li 0.123 520 180.5 0.535 0.98 4 Be 0.090 899 1, 287 1.848 1.57 5 B 0.082 801 2,076 2.46 2.04 6 C 0.077 […]