BORON

Symbol --- B

Abundance --- 0.00086% in earth’s crust

Allotropes --- α-rhombohedral, β-rhombohedral, β-tetragonal

Physical state --- solid

Colour --- black brown

Discovery --- Gay-Lussac and Thenard (1808)

First isolation --- Humphry Davy

Atomic no --- 5

Atomic weight --- 10.81

Period --- 2

Group --- 13 or IIIA

Block --- p

Known isotopes --- ₅B⁸, ₅B⁹, ₅B¹⁰, ₅B¹¹, ₅B¹², ₅B¹³, ₅B¹⁴, ₅B¹⁵, ₅B¹⁶

Stable isotopes --- ₅B¹⁰, ₅B¹¹

Isotopic abundance --- ₅B¹⁰ (19.7%), ₅B¹¹ (80.3%)

Melting Point --- 2348 K (2075 ⁰C)

Boiling Point --- 4198 K (3925 ⁰C)

Density --- 2.45 g/cm³

Density --- 2.08 g/cm³ (liquid)

Electron configuration --- [He] 2s² 2p¹

Electrons per shell --- 2 (1 st shell), 3 (2 nd shell)

Oxidation state --- +3

Valance --- 3

Electronegativity --- 2.04

Electron affinity --- 26.4 KJ/mol

Ionisation energy --- 800 KJ/mol (1 st), 2426 KJ/mol (2 nd), 3659 KJ/mol (3 rd), 25000 KJ/mol (4 th)

Atomic radius --- 90 pm

Covalent radius --- 84 pm

Van der Waals radius --- 192 pm

Ionic radius (B³⁺) --- 27 pm

E⁰(V) --- -0.89 [B³⁺+3e = B(s)]

Crystal structure --- rhombohedral

Heat of fusion --- 50 KJ/mol

Heat of vaporization --- 507 KJ/mol

ΔH⁰_atomisation --- 565 KJ/mol

Molar heat capacity --- 11.08 J/(mol-K)

Specific heat --- 1030 J/ (Kg K)

Thermal expansion --- 5-7 μm/ (m K)

Thermal conductivity --- 27.4 W/ (m K)

Molar volume --- 4.39 x 10^-6

Speed of sound --- 16200 m/s

Magnetic type --- diamagnetic

Lattice angles --- 1.01334, 1.01334, 1.01334

Lattice constants --- 506 pm, 506 pm, 506 pm

Quantum numbers --- ²P_1/2

Neutron cross section --- 760

Neutron mass absorption --- 2.4

Electrical conductivity --- 0.0001 S/m

Electrical resistivity --- 10⁶ Ωm

Mohs hardness --- 9.5

Bulk modulus --- 320 GPa

Vickers hardness --- 49000 MPa