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Chemistry Forums for Students => Undergraduate General Chemistry Forum => Problem of the Week Archive => Topic started by: Borek on March 19, 2012, 11:29:34 AM

This one is completely different. I remember answering this question in the past, but I don't remember where I got it from.
Add 4 more substances to the list:
H_{2}, Li, He, Be, N_{2}, B, O_{2}, C, F_{2}, Na, Ne, Mg...

P Al S Si :X

P_{4}, Al, S_{8}, Si?
Basically UG but in standard states?

Neither is what I expected. Can you explain the logic behind your answer?

This is borderline guess, but the first, third, fifth, etc. elements progress along the periodic table and so do the second, forth, sixth, etc elements.

I see.
OK, it is not the right answer :P

H2, Li, He, Be, N2, B, O2, C, F2, Na, Ne, Mg...
I took the "math sequence" pathI may be way out but  I'll give this a try:
first I put the elements next to its atomic number Then I found what do I need to add or subtract (in atomic number units) to get the next element:for example H is 1, plus 2 gives Li; Li is 3, minus 1 gives He, and so on:
H21 (+2)
Li3 (1)
He2 (+2)
Be4 (+3)
N27 (2)
B5 (+3)
028 (2)
C6 (+3)
F29 (+2)
Na11 (1)
Ne10 (+2)
Mg12 (?)
Then I studied the sequence of signs:
(+  +) ( +  +) ( + +) ( + ?) ( ? ? ?) ( ? ? ?) and I continued the sequence as follows:
(+  +) ( +  +) ( + +) (  + +) (+  +) (+  +).
Lastly the number sequence:
(2 1 2) (3 2 3) (2 3 2) (1 2 ?) ( ? ? ?) (? ? ?) I continued the sequence as:
(2 1 2) (3 2 3) (2 3 2 ) (1 2 1) (2 1 2) (3 2 3)
so putting all together: this will the completed sequence:
( +2 1 +2) (+ 3 2 +3) ( 2 +3 +2) ( 1+ 2+ 1) (+2 1 +2) ( +3 2 +3)
so completing the sequence on the top:
H21 (+2)
Li3 (1)
He2 (+2)
Be4 (+3)
N27 (2)
B5 (+3)
028 (2)
C6 (+3)
F29 (+2)
Na11 (1)
Ne10 (+2)
Mg12 (+1)
Al 13 (+2)
P415 (1)
Si14 (+2)
S816
and I wrote them in standard states as all are on the list:so Al, P_{4}, Si, S_{8} is my answer ;D

I think I got it after trying out many strange approaches for 20min...Cl, K, Ar, Ca?
Highlight text for explanation (possible spoiler): They are following 'gas, solid, gas, etc.' pattern on the periodic table going 1st gas, 1st solid, 2nd gas, 2nd solid so on. Very cool!

you' re right =) I think you got it real cool!

This question is definitely a different one, keen to see the answer.
And that's a lot of typing Ann1234 :o

I think I got it after trying out many strange approaches for 20min...Cl, K, Ar, Ca?
You are on the right track  but still not there.

Cl_{2}, Al, Ar, Si?

Cl_{2}, Al, Ar, Si?
Yep :D

Oops, I see where I made the silly mistakes.