what is meant by angle strain and tetrahedral angle??
Angle strain is the potential energy stored in the molecule due to displacement of bond angles from their equilibrium values.
The equilibrium bond angle values are,
109.5 degree for sp3 hybridized atoms;
120 degree for sp2 hybridized atoms;
180 degree for sp hybridized atoms.
Let us take an example say cyclopropane.
The bond angles of cyclopropane are 60 degrees as its shape resembles an equilateral triangle.
But each carbon is sp3 hybridized and we expect their bond angles to be 109.5 degree. There is a large difference in the bond angles between the actual bond angles (60) and the ideal bond angles (109.5).
This difference in the bond angles result in large angle strain with increase in the potential energy stored in the molecule.
Tetrahedral is a descriptor of the geometry of a molecule in which a central atom forms four bonds which are directed toward the corners of a regular tetrahedron. Tetrahedral geometry forms a solid with four vertices and four sides, all of which are equilateral triangles. Methane is the best example for tetrahedral molecular geometry.
In CH4 molecule, all the four hydrogen atoms are placed symmetrically at the corners of regular tetrahedron joined to central carbon atom by covalent bonds.
Each H-C-H bond angle is 109.5 degree.