Some properties of the alkaline metals

beryllium magnesium calcium

atomic number 4 12 20

atomic weight (stablest isotope) 9.0122 24.312 40.08

colour of element gray silvery white silvery white

melting point (°C) 1,283 650 842–48

boiling point (°C) ~2,500 1,105 1,487

density at 20 °C (grams per cubic centimetre) 1.85 1.74 (5 °C) 1.54

oxidation number 2 2 2

mass number of most common isotopes (terrestrial abundance, percent) 9 (100) 24 (78.70), 25 (10.13), 26 (11.17) 40 (96.97), 42 (0.64), 43 (0.145), 44 (2.06), 46 (0.0033), 48 (0.18)

radioactive isotopes (mass numbers) 7, 10–11 20–23, 27–28 37–39, 41, 45, 47, 49, 50

electrical resistivity at 0 °C (microhm-centimetres) 4.0 4.45 3.91

crystal structure* HCP HCP FCC, HCP, BCC

radius, ionic (+2 ion, angstroms) 0.31 0.65 0.99

diameter, atomic (angstroms) (coordination number of 12) 2.25 3.20 3.93

ionization energy (electron volts)

first 9.32 7.64 6.11

second 18.21 15.03 11.87

third 153.85 80.12 51.21

electrode potential for reduction from the +2 to 0 oxidation state at 25 °C (volts) −1.85 −2.37 −2.87

electronegativity (Pauling) −1.5 −1.2 −1.0

strontium barium radium

atomic number 38 56 88

atomic weight (stablest isotope) 87.62 137.34 (226)

colour of element silvery white silvery white silvery white

melting point (°C) 769 725 700

boiling point (°C) 1,384 1,640 1,140

density at 20 °C (grams per cubic centimetre) 2.54 3.51 (about 5)

oxidation number 2 2 2

mass number of most common isotopes (terrestrial abundance, percent) 84 (0.56), 86 (9.86),87 (7.02), 88 (82.56) 130 (0.101), 132 (0.097), 134 (2.42), 135 (6.59), 136 (7.81), 137 (11.32), 138 (71.66) —

radioactive isotopes (mass numbers) 80–83, 85, 89–93, 95 123, 125–29, 131, 133, 139–43 213–17, 219–30

electrical resistivity at 0 °C (microhm-centimetres) 23 60 —

crystal structure* FCC, HCP, BCC BCC —

radius, ionic (+2 ion, angstroms) 1.13 1.35 1.40

diameter, atomic (angstroms) (coordination number of 12) 4.30 4.48 —

ionization energy (electron volts)

first 5.69 5.21 5.28

second 11.03 10.00 10.14

third — — —

electrode potential for reduction from the +2 to 0 oxidation state at 25 °C (volts) −2.89 −2.90 −2.92

electronegativity (Pauling) −1.0 −0.9 −0.9

*HCP = hexagonal close-packed, FCC = face-centred cubic (cubic close-packed), BCC = body-centred cubic.