Do atoms and molecules affect light rays Molecules of air are all around us all the time. If so, during daylight do rays from the sun diffract as it passes through molecules in the air? and if so is this diffraction negligible to be noticed? plus does this affect anything?
Molecules move at high speeds and at random directions so their diffraction effect must be low, however as their are an infinite number of various air molecules in the atmosphere certainly there must be some sort of effect
Also how and why is the skies blue fixed? (molecules don't stay at the same place they move randomly)  and why isn't the air below the stratosphere seem blue? are there any required criteria's for the diffraction by molecules to be noticeable?
 A: 
Molecules of air are all around us all the time. If so, during daylight do rays from the sun diffract as it passes through molecules in the air? and if so is this diffraction negligible to be noticed? plus does this affect anything?

While both diffraction and scattering refer to redirection, I think scattering is the better term here.  The molecules in the air are sufficient to scatter some of the light as it travels through the atmosphere.  Aerosols also perform some absorption and additional scattering.  I'm not sure what you might mean by "does this affect anything?".

why isn't the air below the stratosphere seem blue? 

There's not enough of it between you and an obvious background.  Water is blue as well.  But in a tall glass, you can't see that.  In a white bathtub, you can probably tell when the water is high.  In a lake or ocean, you can tell easily.  
A: Re: diffraction of light by molecules in the air.
The distances between atoms in molecules is approximately $0.1 nm$ which is about $5000$ times smaller than the wavelength of visible light.
For diffraction effects to occur the structure should have similar dimensions to the wavelength of light - in this case the molecules are just too small for diffraction to occur.
Mark Mitchison#s link above covers the sky is blue...
