Properties of the alkali metals

lithium sodium potassium rubidium cesium francium

atomic number 3 11 19 37 55 87

atomic weight (or stablest isotope) 6.94 22.99 39.1 85.47 132.91 223

colour of element silver silver silver silver silver —

melting point (degrees Celsius) 180.5 97.7 63.28 39.31 28.44 27?

boiling point (degrees Celsius) 1,342 883 759 688 671 677?

density at 20 degrees Celsius (grams per cubic centimetre) 0.534 0.971 0.862 1.532 1.873 —

volume increase on melting (percent) 1.51 2.63 2.81 2.54 2.66 —

valence 1 1 1 1 1 1

mass number of most common isotopes (terrestrial abundance, percent) 7 (92.6), 6 (7.4) 23 (100) 39 (93.1), 41 (6.88), 40 (0.0119) 85 (72.15), 87 (27.85) 133 (100) —

colour imparted to flame red yellow violet dark red blue —

main spectral emission lines (wavelength, angstroms) 6,708; 6,104 5,890; 5,896 7,699; 7,665 4,216; 4,202 4,593; 4,555 —

heat of fusion

(calories per mole) 717 621 558 523 500 —

specific heat (liquid, calories per gram degree Celsius) 1.05 0.33 0.188 0.088 0.0572 —

electrical resistivity at 20–25 degrees Celsius (microhm centimetres) 9.4 4.7 7 12 20 —

magnetic susceptibility

(cgs unit) 14.2 (10⁻⁶) 16.0 (10⁻⁶) 20.8

(10⁻⁶) 17.0 (10⁻⁶) 29.0 (10⁻⁶) —

crystal structure body-centred cubic body-centred cubic body-centred cubic body-centred cubic body-centred cubic —

radius

atomic

(angstroms) 1.52 1.86 2.27 2.48 2.65 —

ionic (+1 ion,

angstroms) 0.9 1.16 1.52 1.66 1.81 1.94

metallic (single

bond,

angstroms) 1.225 1.572 2.025 2.16 2.35 —

first ionization energy (kilocalories per mole) 124.3 118.4 100 96.3 89.8 90.8

oxidation potential for oxidation from the 0 to +1 oxidation state at 25 degrees Celsius (volts) 3.04 2.71 2.92 2.92 2.92 —

electronegativity 0.98 0.93 0.82 0.82 0.79 0.7