hello everyone, i have a question in chemistry
So , when we have to find if a molecule is polar or non polar
Do you know an easy way to do it?
I know we can draw lewis structure and see the lone and bond pairs but this doesnt take time?
i saw a helpfull video on this topic (i will post the link) but im not very sure if i completely understood it
My simplest rule is to check the symmetry of the electron density cloud around the atoms of the molecule.
This video does not talk about polarity or non-polarity, but about 3D structure of molecules. Personally I think it makes it more complicated, because you have to memorize a lot of tricks in it without understanding why the molecules end up in that 3D shape.
I have my own method to construct or visualize the molecules based on understanding of the atoms relative steric occupancy in space in the molecule or compound. The central atom, number of atoms around it and the position of the lone pairs play important roles in visualizing the molecular shape. It is not easy to write a long description of the methods I use. But if you focus on these three factors, you will most probably solve the mystery. 
In some cases, you don’t have a central atom.
can you explain what do you mean by electron density?
i have in my mind these,i dont know if i have understood it correctly
linear=180 degrees=non polar
v shape/bent=104,5=polar
trigonal pyramidal=107=polar
trigonal planar=120=non polar
tetrahedral=109.5=can be non polar or polar
and that the most of the times but not always C,Be,Al,Si form non polar and that P,S,Se form polar compounds
can you correct me if im wrong?
Regarding electron density, you can read this:
Golden Rules of Chemistry (utexas.edu)
Your list looks ok with some remarks:
This link can probably help, although it is a bit at advanced level:
Molecular Geometry – Introductory Chemistry (pressbooks.pub)
Molecules containing a central atom with lone pairs are always polar.
thank you so so much for your help have a good day!!!