elena_333 wrote:Foundational MCQs Q2: Why can't N have 4 bonds and be neutral (as in B)? If it has 5 valence e-, couldn't it form 5 bonds? And similarly, why doesn't it have a charge when bonded only 3 times (as in C)?
Of course, I'm keeping this explanation at GAMSAT level because this matter can get complex quickly and no longer relate to this exam. So, these are the key points: 1) a covalent bond includes 2 electrons, in a normal covalent bond each atom contributes 1 electron to the bond; 2) many common atoms follow the octet rule, the atom is more stable when we can draw a Lewis structure surrounded by 8 electrons; 3) so, as you noted, N has 5 valence electrons so it needs 3 more for the octet and that directly relates to the 3 bonds (recall C has 4 valence and bonds 4 times to be neutral, O has 6 valence and bonds 2 times to be neutral like H2O).
elena_333 wrote:Foundational MCQs Q15: I thought it would be formal charge = 5 - (1+4) = 0, as N has 5 valence e- and is bonded 4 times so has 1 non-bonding e-. Why is it +1?
I believe this is explained above. Please consider looking at the videos on gamsat-prep.com like the 2 for the Periodic Table, and then . . .
Chemical Bonds
Hydrogen Bonds
Ionic and Covalent Bonds
***Lewis Dot Structures
Multiple Bonds