Borane (BH3) is very unstable and quite reactive.
1- explain the source of instability.
The central boron atom lacks an ……..of electrons, and it is therefore very unstable and reactive.
The correct answer and explanation is:
The central boron atom lacks an octet of electrons, and it is therefore very unstable and reactive.
Explanation:
Borane (BH₃) is an electron-deficient molecule, making it highly unstable and reactive. The instability arises due to the fact that the central boron atom has only three valence electrons and forms three single covalent bonds with hydrogen atoms. This results in only six valence electrons around boron instead of the eight electrons required to complete its octet.
In chemical bonding, most main-group elements tend to follow the octet rule, which states that atoms are most stable when they have eight electrons in their valence shell, similar to noble gases. Since boron in BH₃ lacks a full octet, it is electron-deficient, making it highly reactive as it seeks to accept electrons from other molecules or form additional bonds.
Another reason for borane’s instability is its tendency to dimerize. Because BH₃ is so electron-deficient, it spontaneously forms diborane (B₂H₆), where two BH₃ molecules bond together by sharing hydrogen atoms through three-center two-electron (3c-2e) bonds. These bridging hydrogen bonds help stabilize borane in its dimeric form, but monomeric BH₃ remains extremely reactive in isolation.
Additionally, BH₃ is a strong Lewis acid because boron has an empty p-orbital, allowing it to accept electron pairs from Lewis bases. This property makes it useful in organic synthesis, where it forms borane complexes with ligands like tetrahydrofuran (THF) to enhance stability and control reactivity.
Conclusion:
The instability of borane (BH₃) arises from its electron deficiency and its strong tendency to seek additional electrons. This makes it highly reactive, forming dimeric structures and engaging in strong Lewis acid-base interactions.
Here’s a molecular representation of borane (BH₃), highlighting its electron deficiency and reactivity. The image also indicates its tendency to dimerize into diborane (B₂H₆). Let me know if you need any modifications!
