How do you calculate the shape , the hybridisation, the bond angle for a negatively or positively charged compound say (AlCl4)-

Asked by aruni_maiyer | 9th Oct, 2010, 05:12: PM

Expert Answer:

By using formulae:
X= (m+v-c+a)/2
Where,
m = No. of monovalent atoms surrounding the central atom
v = No. of valence electrons in central atom
c and a = cationic or anionic charge (if any)

Instructions:

Collect Data on the Electrons Present in the Molecule

Step 1: Determine which atom is the central atom of the molecule. The central atom is always the most negatively charged atom in the molecule that is neither a halogen nor hydrogen.
Step 2:Determine how many monovalent atoms surround this central atom. A monovalent atom is one that combines with only a single atom to form a molecule.
Step 3: Determine how many valence electrons this central atom has. The valence electrons are the electrons on the outer most shell of the atom.
Step 4: Determine the exact cationic and anionic charges of the entire molecule. Cationic and anionic charges describe the overall positive or negative charge of an atom, with cationic representing the positive charges and anionic representing the negative charges.

Calculate the Hybridization Orbitals
X=2=sp.........linear
X=3=sp2.........triagonal planar
X=4=sp3.........tetrahedral
X=5=sp3d.........triagonal bipyramidal
X=6=sp3d2.........octahedral
X=7=sp3d3
For example,
AlCl4-
Al is central atoms and has 3 (v=3) valence electron and  4 atoms (m=4) of chlorine surrounding the central atom.
hence,
v=3
m=4
cation charge is not present so, c=0 and
a=1
now, x=1/2(3+4-0+1)=4
and for x=4, hybridised shape is sp3, for  sp3 shape is tetrahedral and for tetrahedral the angle is 109o28'

Answered by  | 9th Oct, 2010, 08:00: PM

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