A major challenge in implementing the 'hydrogen economy'
is find...

Question

A major challenge in implementing the 'hydrogen economy' 
is finding a safe, lightweight, and compact way of storing 
hydrogen for use as a fuel. The hydrides of light metals 
are attractive for hydrogen storage because they can store a 
high weight percentage of hydrogen in a small volume. For 
example, NaAlH4 can release 5.6% of its mass as H2 upon 
decomposing to NaH1s2, Al1s2, and H21g2. NaAlH4 possesses 
both covalent bonds, which hold polyatomic anions 
together, and ionic bonds. (d) What is the formal charge on hydrogen 
in the polyatomic ion?

Accepted Answer

Hello. Everyone in this video we want to take a look at sodium borrow hydrated and we're trying to see the formal charge on hydrogen in the poly atomic ion. That's from this sodium borrow hydra. So let's go ahead and rewrite this molecule. We have our NABH four. So we knew we know that this N. A. Here, that's a metal that's going to be our catalon. And that just leaves us with this. The remainder of the molecule, the B. H. four. That's going to be our an eye on then. So N. A. Is going to be in Group one A. And there's going to be a plus one predictable charge. And because we have a neutral compound there must be an ion to balance this. So there was me that the B H four has a negative one charge. It would do the criss cross method. The plus one and negative one will cancel out giving us a neutral compound. And that's exactly what we want. So let's focus now on just our an ion because that's our poly atomic ion. So our boron is in group 38. So there's going to give us three advanced electron per adam. Are hydrogen is in group one A. So there's going to be one valence electron per adam. There's a total of four here. So that's equal to four during the math. That's equal to seven electrons. Now of course we also have to take into consideration our negative one charge are negative one charges means that there's one extra electron. So we'll add one to our son. So seven plus one is equal to eight. And we have a total of eight valence electrons in this poly atomic ion. Now going ahead to draw our lower structure. So we of course have our bond being in the center and then it's connected to four high regions. We know that hydrogen can only make single bonds because of the duet rule. And if you look at the central item it's fulfilled this octet with each of these bonds. And because of this let's just calculate the formal charge on the hydrogen. So the formal charge formula is going to equal to the group number minus apprentices bonds plus our non bonding the electrons. So following this then to our formal charge formula and following this, the hydrogen is in Group 18. So we have that one number of bonds. That's just one as well. Then non bonding electrons just means lone pairs. We don't have any of those. So plus zero. Putting all this into my calculator, I'll get a total of zero. So the formal charge then. So our formal charge on hydrogen In our poly Atomic Ion is going to be zero. And this is going to be our final answer for this problem. Thank you all so much for watching

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