Why NH3 is arranged as a tetrahedron

[primarygun]

why NH3 is arranged as a tetrahedron rather than arranged like the earth(N) is surrounded by 3 satellite(H)?



O=C=O

If is +ve, then it is repelled at its position but it will be attracted if it is at the position of .
Why CO2 is still considered as a non-polar molecule?
is exactly above the C

 

[quetzalcoatl9]

why NH3 is arranged as a tetrahedron rather than arranged like the earth(N) is surrounded by 3 satellite(H)?

Molecular orbitals require that electrons be found in certain places. The "mini solar system" model of the atom (the Bohr model) does not explain covalent bonding.

Are you familiary with VSEPR theory? this may help you:

http://chemlabs.uoregon.edu/GeneralResources/models/vsepr.html

O=C=O

If is +ve, then it is repelled at its position but it will be attracted if it is at the position of .
Why CO2 is still considered as a non-polar molecule?
is exactly above the C

It is not considered to be non-polar, it is non-polar.

a polar molecule is one in which you find an asymmetric charge distribution that gives rise to dipoles on the molecule. there is no such region of electron density on $CO_2$

 

[primarygun]

Thank you.
so the method to find out whether a molecule is non-polar or polar is to draw axis of symmetry on it.
Does this method always work? If not, please tell me what the limitation is.