why does the light of bigger wavelength scatters less than the light of smaller wavelength.

Shorter the wavelength of the light, more is its scattering.

The intensity of scattered sunlight is inversely proportional to the fourth power of wavelength of light.

where I- intensity of scattering light 

          λ- wavelength 

Due to this, the colours having more wavelength scatters less i.e. yellow, orange, red scatters less while colours having shorter wavelength, scatters more i.e. violet, indigo, blue, green scatters more. 

Sunlight is the mixture of these colors. The air molecules on the Earth scatters these colours unequally. 

Even though the violet scatters the most, sky appears to be blue. It's because, the sunlight has more green and blue light than violet and indigo.