Lewis structure of NaBH4 is shown below. NaBH4 is a salt, consisting of the tetrahedral [BH4]− anion.
- Lewis structures, are diagrams that show the bonding between atoms of a molecule, as well as the lone pairs of electrons that may exist in the molecules
How to draw lewis structure
- rules for selecting central atom
- least electronegative or largest size or highest atomic number
- hydrogen and fluorine can never be central atom
- octet of corner atom must be complete ( H - duplet)
- central atom tries to remain in maximum covalency
O = 2 , S = 6, N = 5 ( bond = 4), P = 5, C = 4
- Q (total electron) = valence e⁻ of all atoms + ( -ve charge) - (+ve charge)
- Bond pair e⁻ = 2 × no of bonds , Lone pair e⁻ = Q - B.P e⁻
NaBH4 ⇒ Q = 1 + (3) + (1×4) = 8,
No of bond = 4 so ,B.P e = 8 , L.P e = 8 - 8 = 0
- Since Na is a metal, it will have a (+) charge and BH4 will have -charge. Thus Na wont share electron, it will form an ionic bond.
Formal charge
- The formal charge on an atom in a molecule reflects the electron count associated with the atom compared to the isolated neutral atom i.e. charge present on Na and B atom.
- Formal Charge = [number of valence electrons in neutral atom] – [non-bonded electrons + number of bonds].
- formal charge on Na = 1 -0+0=1
formal charge on B = 3 - 4( bonds) = -1
- BH4, Boron-hydride ion BH4– is formed by the sp3 hybridisation of boron orbitals. Therefore it is a tetrahedral structure.
Thus we can conclude that NaBH4 is tetrahedral in shape.
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