Electrostatic repulsions between lone of electrons on adjacent atoms cause single bonds between N, O, and F to be weaker than expected. Fluorine Chlorine Bromine Iodine Astatine Property atomic symbol F Cl Br I At atomic number 9 17 35 53 85 atomic mass 19.00 35.45 79.90 126.90 210 (amu) valence electron 2s22p5 3s23p5 4s24p5 5s25p5 6s26p5 configuration* melting 114/184 302/— −220/−188 −102/−34.0 −7.2/58.8 point (°C) density (g/cm3) 1.55 (g/L) 2.90 (g/L) 3.10 4.93 — at 25°C atomic radius 42 79 94 115 127 (pm) first ionization 1681 1251 1140 1008 926 energy (kJ/mol) normal (+1, (+1, −1 −1 (+1, +3, −1 oxidation +3, +5, +3, +5, +1 −1 −1, +5, +7) state(s) +7) +7) ionic radius 133 181 196 220 — (pm)† electron affinity −328 −349 −325 −295 −270 (kJ/mol)
Electrostatic repulsions between lone of electrons on adjacent atoms cause single bonds between N, O, and F to be weaker than expected. Property Fluorine Chlorine Bromine Iodine Astatine atomic symbol F Cl Br I At atomic number 9 17 35 53 85 atomic mass (amu) 19.00 35.45 79.90 126.90 210 valence electron configuration* 2s22p5 3s23p5 4s24p5 5s25p5 6s26p5 melting point (°C) −220/−188 −102/−34.0 −7.2/58.8 114/184 302/— density (g/cm3) at 25°C 1.55 (g/L) 2.90 (g/L) 3.10 4.93 — atomic radius (pm) 42 79 94 115 127 first ionization energy (kJ/mol) 1681 1251 1140 1008 926 normal oxidation state(s) −1 −1 (+1, +3, +5, +7) −1 (+1, +3, +5, +7) −1 (+1, +3, +5, +7) −1, +1 ionic radius (pm)† 133 181 196 220 — electron affinity (kJ/mol) −328 −349 −325 −295 −270