Chem Lab C

XXGeneration
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Re: Chem Lab C

Post by XXGeneration » December 2nd, 2011, 8:54 pm

At a first glance I would say that the 2s2 element has a completed subshell (2s) which provides stability.

Likewise, the 2p1 element has a "loose" electron that is in a new subshell, hence it is slightly less stable.

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Re: Chem Lab C

Post by dracomander » December 16th, 2011, 5:52 pm

Periodicity question! there seems to be 2 different conventions for defining electron affinity: one defines EA as the *energy released* when an e- is added, and the other defines EA as the *change in energy* when an e- is added. This changes the sign of the EA value. does anyone know which convention is more common/will most likely be used in scioly?

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Re: Chem Lab C

Post by icyfire » December 16th, 2011, 7:55 pm

@dracomander: on test I've seen, it's only been electron affinity as a negative value...that's just me though

@everyone: why do transition metals form colored compounds?

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Re: Chem Lab C

Post by XXGeneration » December 16th, 2011, 8:20 pm

transition metals form colored compounds because of the unique nature of the d-orbitals. color is the release of energy when an electron moves from a higher energy orbital to a lower one. this is more easily achieved with a d-orbital than in other compounds.

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Re: Chem Lab C

Post by icyfire » January 13th, 2012, 5:41 pm

Does anyone have any good tests or know where to find a good test that has both periodicity and electrochemistry? I've checked the SciOly test exchange, and none of the tests there are both periodicity and electrochem. Thanks in advance

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Re: Chem Lab C

Post by dracomander » January 14th, 2012, 1:31 pm

As far as I know, periodicity has never been a topic before, so I don't think there are any official ones. if anyone knows of one though, I would love to hear about it too.

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Re: Chem Lab C

Post by Skink » January 22nd, 2012, 1:57 pm

icyfire wrote:Does anyone have any good tests or know where to find a good test that has both periodicity and electrochemistry? I've checked the SciOly test exchange, and none of the tests there are both periodicity and electrochem. Thanks in advance
The thing about this is you can find so many introductory college level lecture notes, past exams, etc. online now that you don't necessarily need an SO test to practice this. You won't find the two topics together, but I'd bet you could find plenty separately with a few Google searches.

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Re: Chem Lab C

Post by haverstall » January 23rd, 2012, 6:54 pm

Skink wrote:
icyfire wrote:Does anyone have any good tests or know where to find a good test that has both periodicity and electrochemistry? I've checked the SciOly test exchange, and none of the tests there are both periodicity and electrochem. Thanks in advance
The thing about this is you can find so many introductory college level lecture notes, past exams, etc. online now that you don't necessarily need an SO test to practice this. You won't find the two topics together, but I'd bet you could find plenty separately with a few Google searches.
Not to mention, if you have a dedicated Chem teacher (who doesn't necessarily need to be involved in SciOly), just ask them for questions regarding these topics. They will probably have a boatload of questions ready to dump on you.
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Re: Chem Lab C

Post by anmlee » February 2nd, 2012, 5:27 pm

This is my first time doing Chem Lab, and I have a general idea from my friend who did it before, but I have a few questions regarding the event:

1. My friend said that when she did the event last year, the event was basically about doing an experiment (?). Apparently, the supervisors gave each group a packet, which told them to do certain procedures (i.e. titration), and she and her partner had to do it without any specific instructions on how to do it. In other words, they had to know and understand how to do experiments. I was wondering if this was true for the Southern California competitions?

2. Also, for periodicity...when they mean physical properties, what do they specifically mean? If anyone could give me a list of topics regarding it--for example, periodicity trends, thermochemistry, etc.

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Re: Chem Lab C

Post by XXGeneration » February 2nd, 2012, 6:17 pm

an example of a periodic table trend is:

electronegativity: increases right to left across the periodic table, and increases top to bottom. therefore, fluorine has one of the largest electronegativities, and francium is one of the smallest. this is more likely than not (correct me if I'm wrong) due to having more protons (atomic number increases) compared to the same number of shielding electrons (look this up if you don't get it; it's basically like electrons that don't participate in the bonding shell).


more can be found by googling "trends on the periodic table"

Edit: as for the south californian competitions, can't help you with that as I am from NJ.

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