Some properties of the boron group elements

boron aluminum

atomic number 5 13

atomic weight 10.811 26.9815

colour of element brown silver white

melting point (°C) 2,100–2,200 659.7

boiling point (°C) sublimes 2,550 2,467

density

● solid (grams per cubic centimetre at 20 °C)

2.34 2.699

● liquid (grams per millilitre)

2.34 2.382

valence 3 3

mass number of most common isotopes (terrestrial abundance, percent) 10 (18.8), 11 (81.2) 27 (100)

radioactive isotopes (mass numbers) 8, 9, 12, 13 24–26, 28–30

colour imparted to flame green colourless

colour of ions in solution

● +3

— colourless

● +1

— —

heat of fusion (kilocalories per gram atom) 5.3 2.55

specific heat at 20°C (calories per gram per °C) 0.307 0.214

electrical resistivity at 20–25°C (microhm-centimetres) \\>10¹² 2.65

hardness (Mohs' scale) 9.5 2–2.9

crystal structure at 20°C alpha-rhombohedral, beta-rhombohedral, tetragonal face-centred cubic

radius

● atomic (angstroms)

0.80 1.18

● ionic (+3 ion, angstroms)

(0.20) 0.50

ionization energy (electron volts)

first 8.296 5.984

second 23.98 18.82

third 37.92 28.44

fourth 259.30 119.96

oxidation potential for oxidation from the 0 to +3 oxidation state at 25°C (volts) — 1.67

electronegativity (Pauling) 2.0 1.5

gallium indium thallium

atomic number 31 49 81

atomic weight 69.72 114.82 204.37

colour of element gray blue silver white blue white

melting point (°C) 29.75 156.4 303

boiling point (°C) 2,403 2,000 1,457

density

● solid (grams per cubic centimetre at 20°C)

5.903* 7.31 11.85

● liquid (grams per millilitre)

6.095 11.29

valence 3 3, 1 3, 1

mass number of most common isotopes (terrestrial abundance, percent) 69 (61.2), 71 (38.8) 113 (4.23), 115 (95.77) 203 (29.52), 205 (70.48)

radioactive isotopes (mass numbers) 63–68, 70, 72–76 106–112, 114, 116–124 191–202, 204, 206–210

colour imparted to flame violet blue green

colour of ions in solution

+3 colourless colourless colourless

+1 — — colourless

heat of fusion (kilocalories per gram atom) 1.34 0.78 1.02

specific heat at 20°C (calories per gram per°C) 0.079 0.057 0.031

electrical resistivity at 20–25 °C (microhm-centimetres) 14 8 15

hardness (Mohs' scale) 1.5–2.5 1.2 1.4 (approx.)

crystal structure at 20 °C orthorhombic face-centred tetragonal hexagonal close-packed

radius

● atomic (angstroms)

1.25 1.50 1.71

● ionic (+3 ion, angstroms)

0.62 0.81 0.95

ionization energy (electron volts)

first 6.00 5.79 6.106

second 18.9 18.86 20.42

third 30.70 28.0 29.8

fourth 64.2 57.8 50

oxidation potential for oxidation from the 0 to +3 oxidation state at 25 °C (volts) 0.52 0.34 −1.25

electronegativity (Pauling) 1.6 1.7 1.8

*Density at 25 °C