If the HCH angle within the methane molecule is 109.5�, what is the H&H bond angle within ammonia? All right, so here we're to draw chapter 4. Carbon will go in the center. Carbon has four valence electrons. Hydrogens are in Group 1A, so they only have one valence electron. OK, so then here's our structure and they're just saying here that our bond angle between hydrogen, carbon, hydrogen is 109.5�.
Now if we're to draw ammonia, nitrogen's in Group 5A, so it has five valence electrons. Three of them would be used to connect to the three hydrogens that we have. Now here we have a lone pair on the nitrogen. And remember, when we have that lone pair on the nitrogen, it causes our bond angle to decrease to become smaller.
So we would expect the bond angle to be a number smaller than one O 9.5. It'd be less than one O 9.5. So if we take a look here, the only degree that we see as an option that's less than 109.5 is option C. The bond angle in the ammonia molecule between H&H is approximately one O 7.3�.