Boron (B) is an element with an atomic number of 5, which means it has five electrons in its neutral state. Two of these electrons are in the inner shell, and the remaining three electrons are in the valence shell. Boron typically forms compounds by sharing electrons in covalent bonds, allowing it to achieve a stable electron configuration.
Boron's electron configuration is 1s² 2s² 2p¹, with one unpaired electron in the 2p orbital. While boron has three valence electrons, it can still form compounds like boron trihydride (B2H6), also known as diborane. This is due to a phenomenon called "electron-deficient bonding" or "electron pair deficiency."
In diborane, two boron atoms are connected by a bridge of two hydrogen atoms. Each boron atom donates one electron to form a total of four bonding electrons. These electrons participate in the formation of four covalent bonds, resulting in a structure with two B-H-B bridges.
The electron-deficient bonding in diborane occurs because each boron atom only has six electrons around it instead of the usual eight electrons (octet rule). This situation is stabilized by the presence of bridging hydrogen atoms that contribute their electron pairs to form additional bonds.
In summary, even though boron has only three valence electrons, it can form compounds like diborane (B2H6) by utilizing electron-deficient bonding, where boron atoms share electrons and bridge hydrogen atoms contribute additional electron pairs to stabilize the structure.