Some properties of the boron group elements

Some properties of the boron group elements

Table
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
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Universalium. 2010.

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