[Ashutosh]

I dont understand MOT.I know 1S orbital (first orbit) contain maximum 2 electrons.But I think sigma 1S & sigma*1s orbital are in the first orbit. Is it right ???according to this,electrons are filled in these orbital first.so,max.number of electron in 1 orbit is 4.is this not contractory with the second statement
 thanking you.

[AWK]

Two electrons are either on 1s or 1s*

[Donaldson Tan]

1s* exist?

i thought antibonding orbitals only exist for molecular orbitals, not atomic orbitals. antibonding orbitals arises when 2 atomic orbitals of -ve sign overlap with each other? how can there be such thing as 1s*?

[Ashutosh]

Two electrons are either on 1s or 1s*

   according to MOT ,electrons are filled sequensially in 1S and then in 1S*.I think it is not possible to have electrons either on 1S or on 1S*.
             
                 another question
  when each two electrons filled in the 1s and 1S* then total number of electrons in the first orbit =4.how is it possible

[Mitch]

Your confusing sigma orbitals with s orbitals.

MOLECULAR ORBITAL THEORY IS ONLY USED WITH BONDING: As such you will always have more then one atom present when you envoke MO theory.

A rule in MO Theory is that you need to have as many moleular orbitals as you have atomic orbitals. So, in the case of H2, where both hydrogens will donate their 1s orbital, for a total of two 1s orbitals. Correspondingly, two sigma orbitals need to be made as well the sigm bonding and the sigma antibonding.

Hope that helps.

Mitch

[Ashutosh]

Thanks Mitch for helping.I get my difficulty cleared