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# Amount of substances watch

1. Hey guys,
I have my mock exam next week and I'm really stuck with these questions. Well I know they're so easy but I can get them
Can please anyone explain them to me.
Thanks
(1)- Which one of the following does not have a pair of s electrons in its highest filled electron energy sub-level? H–, Mg, P3+, Ar
(2)- Which one of the following atoms has only two unpaired electrons inits ground (lowest energy) state? helium, beryllium, nitrogen, oxygen
(3)- Assuming that chlorine exists as two isotopes, and that hydrogen and carbon exist as one isotope each, how many molecular ion peaks will be shown in the mass spectrum of C4H6Cl4? 1, 2, 3, 4, 5
2. Nice question!

Chemistry with all its abstractness can definitely be quite challenging to comprehend at first. Good luck with your mocks and I'll take each one in turn.

1. Which one of the following does not have a pair of s electrons in its highest filled electron energy sub-level? H–, Mg, P3+, Ar
The method: It's a weird question, but essentially its asking which of these elements/ions don't have both:
1. An S orbital as its highest energy level
2. Paired electrons in its S orbital (i.e. 2 electrons or a Xs^2 where X is just the principle energy level: 1, 2, 3 etc)

Lets look at each in turn:
H-: Hydrogen by itself have one electron, so it would normally be 1s^1. But since its H-. its gained 1 electron, and this electron fills the lowest energy level which is the 1s orbital forming now a 1s^2 orbital (now there are two electrons there. Highest energy level is an s orbital? Check. Pair of electrons in its s orbital? Check.
Mg: The electron configuration of Magnesium is 2.8.2 or for us A level people its 1s^2, 2s^2, 2p^6 and finally 3s^2. Highest energy level is an s orbital? Check (that's our 3s^2). Pair of electrons in its s orbital? Check (that's where the ^2 comes in).
P3+: This is phosphorus 3+. The electron configuration is 1s^2, 2s^2, 2p^6, 3s^2, 3p^3. But wait. This is phosphorus 3+, so it must have lost three electrons (hence why it is positively charged). So lets take off 3 electrons, from the highest energy levels. The electron configuration is now: 1s^2, 2s^2, 3s^2... and that's it. (Bye bye 3p orbital electrons). Highest energy level is an s orbital? Check. Pair of electrons in its s orbital? Also check.
Ar: Technically you could just say, well Argon's the only one left so it must be this. But, lets look at it anyway. Electron configuration: 1s^2, 2s^2, 2p^6, 3s^2, 3p^6. Highest energy level is an s orbital? Nope. Pair of electrons in its s orbital? Yes.
But since its highest energy level is not an s orbital, Ar is the odd one out (since its highest energy level is a p orbital)

2. Which one of the following atoms has only two unpaired electrons inits ground (lowest energy) state? helium, beryllium, nitrogen, oxygen
Again lets look at each in turn (now I will separate out the p orbitals in 2px, 2py and 2pz, since there are three of them). Remember that the orbitals fill up one at a time, before pairing up.
Helium: 1s^2 - no unpaired electrons so a definite no.
Beryllium: 1s^2, 2s^2 - no unpaired electrons, so again, a big no.
Nitrogen: 1s^2, 2s^2, 2px^1, 2py^1, 2pz^1 - unpaired electrons - 3 of them so again no.
Oxygen: 1s^2, 2s^2, 2px^2, 2py^1, 2pz^1 - 2 unpaired electrons ( in the py and pz orbitals) so yes its oxygen.

3. Assuming that chlorine exists as two isotopes, and that hydrogen and carbon exist as one isotope each, how many molecular ion peaks will be shown in the mass spectrum of C4H6Cl4? 1, 2, 3, 4, 5
Ok this is just a good old, long, boring question. if chlorine exists in two isotopes, I'll just label them X and Y.
Each isotope has a slightly different mass, and so they will show up differently on the mass spectrum.
The combinations are:
C4H6XXXX
C4H6XXXY
C4H6XXYY
C4H6XYYY
C4H6YYYY

and so, the answer is 5!

Disclaimer: I'm just an A level student myself, and I would probably struggle also (well I struggle with everything!), so take my answer with a pinch of salt!

I hope I've helped at least a tiny bit!
3. (Original post by Spectral)
Nice question!

Chemistry with all its abstractness can definitely be quite challenging to comprehend at first. Good luck with your mocks and I'll take each one in turn.

1. Which one of the following does not have a pair of s electrons in its highest filled electron energy sub-level? H–, Mg, P3+, Ar
The method: It's a weird question, but essentially its asking which of these elements/ions don't have both:
1. An S orbital as its highest energy level
2. Paired electrons in its S orbital (i.e. 2 electrons or a Xs^2 where X is just the principle energy level: 1, 2, 3 etc)

Lets look at each in turn:
H-: Hydrogen by itself have one electron, so it would normally be 1s^1. But since its H-. its gained 1 electron, and this electron fills the lowest energy level which is the 1s orbital forming now a 1s^2 orbital (now there are two electrons there. Highest energy level is an s orbital? Check. Pair of electrons in its s orbital? Check.
Mg: The electron configuration of Magnesium is 2.8.2 or for us A level people its 1s^2, 2s^2, 2p^6 and finally 3s^2. Highest energy level is an s orbital? Check (that's our 3s^2). Pair of electrons in its s orbital? Check (that's where the ^2 comes in).
P3+: This is phosphorus 3+. The electron configuration is 1s^2, 2s^2, 2p^6, 3s^2, 3p^3. But wait. This is phosphorus 3+, so it must have lost three electrons (hence why it is positively charged). So lets take off 3 electrons, from the highest energy levels. The electron configuration is now: 1s^2, 2s^2, 3s^2... and that's it. (Bye bye 3p orbital electrons). Highest energy level is an s orbital? Check. Pair of electrons in its s orbital? Also check.
Ar: Technically you could just say, well Argon's the only one left so it must be this. But, lets look at it anyway. Electron configuration: 1s^2, 2s^2, 2p^6, 3s^2, 3p^6. Highest energy level is an s orbital? Nope. Pair of electrons in its s orbital? Yes.
But since its highest energy level is not an s orbital, Ar is the odd one out (since its highest energy level is a p orbital)

2. Which one of the following atoms has only two unpaired electrons inits ground (lowest energy) state? helium, beryllium, nitrogen, oxygen
Again lets look at each in turn (now I will separate out the p orbitals in 2px, 2py and 2pz, since there are three of them). Remember that the orbitals fill up one at a time, before pairing up.
Helium: 1s^2 - no unpaired electrons so a definite no.
Beryllium: 1s^2, 2s^2 - no unpaired electrons, so again, a big no.
Nitrogen: 1s^2, 2s^2, 2px^1, 2py^1, 2pz^1 - unpaired electrons - 3 of them so again no.
Oxygen: 1s^2, 2s^2, 2px^2, 2py^1, 2pz^1 - 2 unpaired electrons ( in the py and pz orbitals) so yes its oxygen.

3. Assuming that chlorine exists as two isotopes, and that hydrogen and carbon exist as one isotope each, how many molecular ion peaks will be shown in the mass spectrum of C4H6Cl4? 1, 2, 3, 4, 5
Ok this is just a good old, long, boring question. if chlorine exists in two isotopes, I'll just label them X and Y.
Each isotope has a slightly different mass, and so they will show up differently on the mass spectrum.
The combinations are:
C4H6XXXX
C4H6XXXY
C4H6XXYY
C4H6XYYY
C4H6YYYY

and so, the answer is 5!

Disclaimer: I'm just an A level student myself, and I would probably struggle also (well I struggle with everything!), so take my answer with a pinch of salt!

I hope I've helped at least a tiny bit!
Thanks so much this really helped .. Now I got it, this morning I was so confused with it but u made it easier for me thanks again

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