diatomic are always linear whereas polyatomic have multiple shapes they can take
same type of stuff at the diatomic lewis model, make the valence electron fulfil the octet rule. the second period will never have more that 8 valence electrons but they might have less. if there are fewer that 8 electrons then we call the atom electron poor. this equates to a very reactive molecule
as we move down the periodic tabel we can start to break the octet rule . this is usually in the p-block elements. when atoms have more than 8 electrons in the valence shell, both the atom and the molecule gets the label fo hypervalent
we work out the charge son each of the atoms and then the correct structure will be that with the lowest summed charge.
we can work ti out by finding the difference between the number of valence electrons in isolated atom and the number of electrons assigned toa atom in the lewis structure. then divide electrons int oa covalent bond equally
$\text{formal charge= no. electrons in valence of free atom - no. of bonds to atom - no. of unshared electrons}$
valence shell elctron pair repulsion
this is a simple way to predicting the shapes of molecules that assumes that only valence electrons influence molecular shape. this model works best for p-block elements. this is a predictive model
electron pairs repell each other, and so they take positions as far away from each other
repell 2.5ยบ more then electron dense areas
double bond occupy more space