A NEW TYPE OF NITROGEN - Periodic Table of Videos

0:00 In June this year, a paper was published

0:05 which is really important about

0:07 nitrogen.

0:08 People get very excited about

0:11 so-called allotropes of elements.

0:14 Elements that can exist in different

0:17 forms.

0:18 Graphite and diamond for carbon.

0:21 O2 and ozone for oxygen.

0:25 Phosphorus can be red phosphorus, white phosphorus,

0:29 black phosphorus.

0:31 But nitrogen has just N2 and a form

0:36 called black nitrogen, which we gave a

0:39 video about quite recently,

0:42 but which only exists at some enormously

0:46 high pressure and isn't black anyway.

0:50 But now this paper describes a new form

0:56 of nitrogen which is called N6

1:00 nitrogen atoms.

1:02 They have called it C2H

1:05 N6 where C2 is nothing to do about

1:09 carbon but describes the shape of this

1:14 molecule and you can see it here.

1:17 It has three nitrogens in a row here, three here, and

1:22 it's joined by a bond more or less at a

1:25 right angle.

1:26 So, it's a funny zigzag

1:28 molecule.

1:29 So, I won't go through the

1:31 boring explanation, but the C2H

1:36 means it's got this zigzag shape refers

1:40 to the symmetry of the molecule.

1:42 So, why have I got excited about it?

1:44 There are three reasons.

1:46 Firstly, new form of

1:48 nitrogen.

1:50 Secondly, it uses a technique called

1:54 matrix isolation that I used to use for

1:58 my doctorate and for some years

2:01 afterwards, a low temperature technique.

2:04 And thirdly, because I thought of an

2:07 analogy about this molecule which the

2:10 authors hadn't.

2:12 The difficulty of making

2:14 allotropes of nitrogen is that N2 the

2:19 common form of nitrogen has a very

2:22 strong bond between the two nitrogen

2:25 atoms.

2:26 In fact, it's the strongest bond

2:29 between two atoms that are the same

2:33 anywhere in the periodic table.

2:35 And this means that if you make a molecule with

2:39 nitrogen atoms with different sorts of

2:42 bonds between them, then it can

2:45 decompose very easily into N2 molecules

2:50 with a huge release of energy.

2:52 it would be explosive

2:55 and therefore it will be very unstable.

2:58 Although N2 is a stable form, you can

3:02 make ions.

3:04 These are negatively charged

3:07 groups of nitrogen most famously

3:11 so-called aid which consists of three

3:16 nitrogen atoms in a row with a negative

3:19 charge.

3:20 So it's N3 minus and this can

3:23 form salts.

3:24 On our video about the

3:26 element nitrogen, you can see a

3:28 demonstration with sodium aid which

3:32 decomposes with a big flame when Neil

3:36 heats it.

3:38 And the experiment to make N6 uses

3:42 silver aside which is a much more

3:45 explosive compound.

3:47 We don't have any

3:48 here in the chemistry department at

3:51 Nottingham so I can't show you any.

3:53 The idea of the experiment

3:56 to make this was to treat silver aid

4:00 with either chlorine or bromine gas to

4:04 convert the silver to silver broomemide

4:06 or silver chloride and to get two aid

4:10 radicals to stick together to make N6.

4:15 and the extra electrons from N3 minus

4:19 transfer to the chlorine or the bromine

4:23 to make chloride or bromide.

4:26 The difficulty is how to stabilize

4:31 the N6 if you make it.

4:35 And the way this was done was to use

4:38 solid argon at 10°

4:42 Kelvin.

4:43 That's -263 Celsius.

4:49 And the molecules of N6 then get trapped

4:55 in the solid argon rather like the

4:58 cherries in the cake that you can see in

5:01 the photograph.

5:02 So once it's trapped in

5:04 the argon at very low temperature, it

5:07 can't decompose.

5:08 Is it just like it's like kind of like

5:10 frozen in it like Han Solo and

5:12 carbonite?

5:14 Like what?

5:16 I'll I'll explain later.

5:19 It's a Star Wars reference.

5:21 Okay.

5:22 Well, as long as the viewers will

5:24 understand it.

5:24 But once the N6 is stuck

5:27 in the argon, how on earth can you tell it's there?

5:33 And the answer is that because it has

5:36 atoms of nitrogen which vibrate even at 10 Kelvin, they

5:43 will absorb infrared light and give a

5:46 characteristic pattern.

5:48 and argon because it has only one atom in the

5:52 molecule cannot vibrate and so it doesn't absorb

5:57 the infrared light.

5:58 What you can do

6:00 is that if you look at the spectra that

6:03 have been published in their paper,

6:07 there are quite a few different bands in

6:10 the spectra.

6:11 To decide which of the

6:12 bands belong together, you can shine

6:15 light onto the argon.

6:18 The light is absorbed by the N6

6:22 and so the energy is enough to destroy

6:25 the molecule.

6:27 And there's only a small

6:28 amount.

6:28 So the whole apparatus doesn't

6:30 blow up.

6:31 But the infrared bands

6:32 disappear and you can see them going

6:35 down at the same rate.

6:37 So you know they

6:38 belong to the same molecule.

6:40 But you still need a bit more information.

6:42 And the authors did quite a clever

6:45 experiment in which they used a

6:48 different isotope of nitrogen.

6:51 Nitrogen has two types of atoms.

6:54 the more common one, nitrogen 14,

6:57 and a rarer form called nitrogen 15 that

7:01 has an extra neutron.

7:03 It's chemically identical to nitrogen 14, but it's

7:06 heavier.

7:07 And so when it vibrates, it

7:10 vibrates at a lower frequency

7:13 because it's heavier.

7:15 So they used aid,

7:18 which had one nitrogen 15 and two

7:22 nitrogen 14.

7:23 So this bond will vibrate

7:25 at a different frequency from that one.

7:29 And you can imagine they can join

7:32 together like this or they could join

7:36 together like that and so on.

7:38 So you get more infrared bands and you get more

7:42 information and then using computer

7:45 modeling you can confirm what you've

7:47 really got.

7:48 I was very excited by this.

7:51 When I did matrix isolation, I used

7:54 isotopes as well.

7:56 In my case, 13 carbon,

7:58 but the principle was similar.

8:01 This experiment gave me great pleasure

8:04 because made me nostalgic, but also I

8:08 could see how the authors were thinking.

8:12 The team led by Professor Peter Shriner

8:15 wondered whether the argon was really

8:17 necessary to stabilize it.

8:20 And so they did the experiment again without the

8:22 argon and froze a thin film of N6.

8:29 Disappointingly, it's not colored.

8:31 So there's no nice photo of N6.

8:35 But you've never seen it.

8:37 How does that feel?

8:39 Well, that's the fate of a chemist.

8:40 you know you most of the time you don't

8:42 don't see your stuff I mean let's say

8:44 you can isolate a white powder and said

8:46 this is aspirin it might as well be

8:49 10,000 other things so we always have to

8:52 rely on secondary evidence that you know

8:54 from spectroscopy to know what we have

8:57 so for me it's a normal feeling and uh

8:59 in quotes I have seen it you know

9:01 looking through the little window and

9:03 saying there is a film and you know it

9:05 doesn't look like anything but at least

9:07 I have seen it

9:09 the infrared spectrum showed that even

9:11 without the argon, it was stable even at

9:14 the temperature of liquid nitrogen which

9:16 is 77 Kelvin.

9:19 So the idea is that

9:21 potentially you could use this material

9:26 as a storage of energy if you like an

9:31 explosive.

9:32 Aides are sometimes used in

9:35 airbags for cars.

9:37 Now, I don't think N6

9:39 would be used for that, but you could

9:41 imagine applications where it might be

9:43 useful.

9:47 Bombs,

9:46 I don't think it would be useful for

9:49 bombs.

9:50 It's too unstable.

9:52 You don't want a bomb that is going to

9:54 go off before you're ready for it to

9:57 detonate.

9:58 Any energetic molecule, highly energetic

10:00 molecule, you can think of applications,

10:02 you know, in the extreme case as rocket

10:05 fuel.

10:06 So we are now uh actually writing

10:08 with a um basically with rocket

10:11 scientists proposal to our government to

10:14 develop this um you know scale it up and

10:16 see what kind of thrust you can

10:17 generate.

10:18 And the cool thing about it is

10:20 you would only generate air, you know,

10:22 when it ignites.

10:24 And it would do all of

10:25 this without a flame uh and without

10:28 condensation.

10:29 So it would alleviate a

10:30 lot of the problems that rockets have

10:32 nowadays.

10:35 A second one is uh to use it as an

10:38 energy storage material if it can be

10:40 handled safely.

10:41 So we're thinking about

10:43 um ways of um embedding it into uh you

10:48 know for instance metal organic

10:50 frameworks um to stabilize it and then

10:53 perhaps have you know energy released on

10:55 command from something that again

10:57 produces only air.

11:00 That brings me to

11:03 the thought that I had that professor

11:06 Shriner hadn't had.

11:08 There is an idea in

11:09 inorganic chemistry called pseudo halogens.

11:14 A halogen the elements in group 17

11:19 florine, chlorine, bromine and so on.

11:22 And pseudo halogens are groups of atoms

11:27 which behave in a very similar way to a

11:30 h hallogen.

11:32 They will form salts.

11:35 So you can imagine that aid can form N3

11:40 minus.

11:41 They can form acids

11:44 like HCl or HF and you can get HN3.

11:50 And therefore it struck me that N6

11:54 is the pseudoanalogue of chlorine

11:58 because you have two of these pseudo

12:01 halogen groups joined together.

12:05 So I wrote to professor Shriner who said

12:09 that he hadn't thought of it and he

12:12 didn't think other people had thought of

12:14 it and he was very pleased because

12:16 otherwise they might have done the

12:18 experiment first.

12:19 It also suggests how

12:23 the research might go next

12:26 because nitrogen forms quite an unstable

12:31 compound which is N3 nitrogen

12:35 tricloride.

12:36 So you can imagine having

12:38 nitrogen triazide N3 three times

12:45 which would be nitrogen 10

12:48 and that would be really quite a nice

12:51 allotrope and I think professor Shriner is now

12:55 trying to make that.

12:57 It will probably be possible to make N10

13:01 uh which uh is even crazier.

13:04 My hope is that as they get bigger that also get

13:06 more stable uh because they may become

13:09 solids and solids tend to be know more

13:11 robust in terms of you know energy

13:13 release.

13:15 Um and let's see where we can

13:16 go.

13:17 But that's that's what we're

13:18 targeting right now.

13:20 Professor, I've seen that distinctive

13:21 shape of N6.

13:22 What shape would N10 be?

13:26 It would be an N in the middle with

13:28 three N3 arms or like a like a star with three arms.

13:33 Yeah.

13:33 So, actually pretty nice.

13:35 He sent me some really nice pictures of

13:39 his equipment.

13:41 He also show sent us a

13:43 nice photo of himself.

13:45 So, I think he should be congratulated

13:48 on doing a really interesting experiment

13:51 to make people think.

13:53 His apparatus is really nicely engineered.

13:58 Looks quite similar to the equipment I

14:00 used.

14:01 And in fact, Brady will show you a

14:04 few shots of the equipment that I used

14:07 to use and is now stored just for old

14:11 time's sake.

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