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Test 2 Question 4 about hybridization
The structure of tetravalent carbon compounds could not be adequately explained using the electron configuration of carbon
1s(2), 2s (s),2px(1) 2py(1) 2pz(0)
*the number in brackets indicates the number of electrons in that orbital.
For the carbon atom , in order to form 4 bounds with other atoms, it needs 4 unpaired electrons in 4 different orbitals.
Therefore the 2s orbital was mixed with the other three 2p orbitals(2px,2py,2pz) and 4 new orbitals were obtained-called molecular orbitals.
This process is known as hybridization and sp3 comes from the fact that one "s" orbital is mixed with three "p"orbitals.
The new structure of carbon looks like
1s(2), sp3 (1) sp3(1) sp3(1) sp3(1)
Now carbon can form 4 bonds with 4 other atoms.
Whenever a carbon atom is bounded to 4 other atoms it has a sp3 hybridization(it needs 4 orbitals and 1 from s and 3 from p makes it, 1+3=4) like in CH4, or CH3-CH3.
When it is bounded to 3 atoms -like in CH2=CH2, it has sp2 hybridization.(it needs 3 orbitals and 1 s and 2 p makes it, 1+2=3)
When it is bounded to 2 atoms like in C2H2, it has a sp hybridization (it needs 2 orbitals and 1 s and 1 p makes it, 1+1=2.)
The sp3d, and sp3d2 involves the same concept but with atoms from the third period on and it is unlikely to appear in sat questions.
Hope this was useful.
Will you post a new test each day? If so, thank you!
Yes, a new test will be posted every day. There is also a new challenge - the SAT Question of the Day, but its level of difficulty is higher than the average SAT question.
do v get to use a periodic table and calculator on the sat II chemistry test ?
also can u describe the differences between directional covalent and nondirectional covalent bonding ?? i didnt really understand those things much .. thx
how do u expect me to do on the SAT II chem test if I am taking AP Chemistry? to be honest my class is REALLy far behind so i'm reading on my own but am still pretty much understanding the material. and if i have questions i ask my teacher. so do you think i would be well prepared to take the SAT II subject test for chemistry?
A periodical table indicating the atomic numbers and masses of elements will be provided but NO calculator will be allowed during the SAT exam.
Directional and non directional bonding are related usually with ionic and covalent bonds.
When we speak about the directional and nondirectional bonding within a covalent bond, we usually refer to the rigidness and localization of a bond.The most simple answer is this : Sigma bonds are directional - they are well defined, rigid,-while nondirectional bonds are "pi" usually unlocalized and with more "freedom" for electrons.
ohhhhhhhhhh ok thx. that helps a whole bunch
How do u synthetize 1,3 dichloro benzene?
There are different methods for the synthesis of it, and they depend on the starting substances - what you have available.
Anyway this kind of questions you will NEVER encounter at SAT.
are your test questions harder than the actual sat questions too ?
No, only the SAT question of the Day is harder.
The test questions are like regular SAT questions- this does not mean that all of them have the same difficulty level, but they fit in the SAT difficulty range.
oh ok .. cuz i find ure test questions harder than the your questions of the day
Uhmm why does Oxygen have a greater electronegativity? they are the same distance from Fluorine. Is this something I need to memorize?
which question are u talking about
test 6
#8
Also if you know. HOw do you determine how many isomers tehre are for a compound?
electronegativity increases across a period and decreases down a group .. and im pretty sure the decrease down a group is a greater "jump in decrease" than the "increase across a period" .. so I would be the most electronegative .. and for the isomers thingy .. i think u just use trial and error type deal ... keep tryin to see how many u can get and try not get doubles in there ..
Charlie, there is not a certain formula to determine the number of isomers for a substance.You just have to write all the compounds with that molecular formula that come to your mind and make sure not to miss or repeat any of them.
Oxygen is more electronegative than the Chlorine.There is a decrease in electronegativity of about 1.0 down in the halogen group while in the period there is a decrease of about 0.5 from the right side to the left. For example F has an electronegativity around 4 , O has 3.5 and chlorine 3.0;However the actual values for the electronegativity are not well defined because they can be calculated in different ways giving different results(even if quite similar). Therefore you should know only the relative electronegativity of an element I mean just to have an idea to compare them. Fluorine is the most electronegative one and Cesium the least.They increase across a period from left to right and decrease down in group.
how do you synthesize 1,3 dichlorobenzene starting from benzene??/
C6H6+HONO2->(H2SO4)C6H5-NO2 + H2O
C6H5-NO2+ Cl2---->(FeCl3 0 degrees C)
-----> NO2-C6H4-Cl(Cl is in META, 3)[1 nitro, 3-Cl benzene]
NO2-C6H4-Cl+HONO-->NH2-C6H4-Cl+N2+H2O
NH2-C6H4-Cl+CuCl--->(CuCl its used to catalyze too)---> Cl-C6H4-Cl
I have a question from my AP class:
The table below summarizes the reactions of a certain unknown solution when treated with bases:
Sample I: Reagent (NaOH (aq))
Results: (limited amount of reagent: white precipitate) and (excess reagent: precipitate dissolves)
Sample II: Reagent (NH3 (aq))
Results: (limited amount of reagent: white precipitate) and (excess reagent: white precipitate)
Which of the following metallic ions could be present in the unknown solution?
(A) Ca2+ (aq)
(B) Zn2+ (aq)
(C) Ni2+ (aq)
(D) Al3+ (aq)
(E) Ag2+ (aq)
Thanks in advance for your help!
I think its Ag+2
because In presence of NH3(aq) which is in fact NH4OH it forms
[Ag(NH3}2]OH, and in the pesence of NaOH first it forms Ag(OH)2 and then Na[AgOH]OH or sth like that i dont know for sure
The answer is D - Al3+
The first condition is fulfilled only by Zn and Al
Zn2+ + 2NaOH => 2Zn(OH)2+ 2Na+
so a white precipitate is formed
Zn(OH)2 + 2NaOH => Na2[Zn(OH)4]
the white precipitate is dissolved.
Al3+ + 3NaOH => Al(OH)3 + 3Na+
white precipitate formed
Al(OH)3+ NaOH => Na[Al(OH)4]
the precipitate is dissolved
For the second reaction both form the white precipitate(the hydroxide ) with ammonium
but the zinc one is dissolved in excess
Zn(OH)2 + 4NH3=> [Zn(NH3)4]2+ + 2OH-
while the aluminum is not dissolved
hope this helped.
dang .. how are you supposed to konw all of that though ?
Thanks. But why do Na2[Zn(OH)4]and [Zn(NH3)4]2 dissolve?
Also, I have another question. :)
HCl>HC2H3O2>HCN>H2O>NH3
Five acids are listed above in the order of decreasing acid strength. Which of the following reactions must have an equilibrium constant with a value less than 1?
(A) HCl+ CN- <=> HCN +Cl-
(B) HCl + H2O <=> H3O+ + Cl-
(C) HC2H3O2 + OH- <=> C2H3O2- + H2O
(D) H2O + NH2 <=> NH3 + OH-
(E) HCN + C2H3O2- <=> HC2H3O2 + CN-
Again, thanks for your help.
Also, in your explanation above:
"For the second reaction both form the white precipitate(the hydroxide) with ammonium"
Where did the hydroxide come from? I don't see how Al3+ and ammonium forms a hydroxide
which bonds are stronger..covalent or ionic ?
Anonymous said...
Thanks. But why do Na2[Zn(OH)4]and [Zn(NH3)4]2 dissolve?
The precipitate -Zn(OH)2 dissolves and forms Na2[Zn(OH)4]and [Zn(NH3)4]2
which are clear solutions.
NH3 dissolved in water is actually NH4OH; NH3+ H2O = NH4OH
so
Al3+ + 3NH4OH = Al(OH)3 + 3NH4+
The same for zinc
The answer to your question is E;
General method to be used:
Every acid base reaction that is wrote can be depicted as:
HA+B- => HB + A-
Ke = [HB][A-]/[HA][B-] =
= [H3O+][HB][A-]/[HA][B-][H3O+]
and Ka HA = [H3O+][A-]/[HA]
Ka HB = [H3O+][B-]/[HB]
and you find out
Ke = Ka(HA) /Ka(HB)
From the acidity strength list you can find which Ka is greater- the stronger the acid the greater the Ka and you find when Ke is less than 1 (when Ka (HB)is greater than Ka (HA)).
Is it true that ionic bonding is the strongest attractive inter/intra molecular force and that Hydrogen bonding is the strongest type of bond?
i always thought it was like this (from strongest to weakest):
ionic, covalent, metallic, hydrogen bonding, polar, dipole, and finally LD forces .. i always thought of them as all being either forces or bonds .. not some being bonds and some being forces ..
i mite be wrong though ... =/
You should differentiate between intermolecular and intramolecular forces.
Intermolecular forces (non-bonding)
ion-dipole interactions > Hydrogen forces > dipole-dipole > Dispersion London
Intramolecular forces (bonding)
Ionic > covalent > metallic
The intramolecular forces are obviously greater than the intermolecular ones.
I don't have a question about the SAT II itself, but I don't know where else to ask it. I would like to know what are the best Chemistry universities in the USA? I mean ,where is the best place in the USA to study chemistry? Is there on the Internet a site that kepps an evidence of this kind or something like that?
id probably say all those techy schools like MIT, Georgia Tech, Berkeley, Cal Tech, Stanford and obviously Harvard .. mayb John Hopkins though ? .. cuz i know its best for medical .. not sure though ..
In the order of decreasing acid strength is HCl or H2SO4?
Thanks for your help.
H2SO4 is like 100 times stronger than HCl
i just wanted to know what would be good to study for the test because i am in chemistry honors and theres things like organic compounds that we have not learned...so if you could help and tell me what would be good to know for the test
i want to know what is a " bond order".. i appreciate your help
6. Contains sp hybridised carbons.
(A) CH4
(B) CH3COOH
(C) CH3CH2OH
(D) C2H2
(E) CH3OCH3
could you explain this question?
Are there any special strategies for the test? Also what laws are needed, and do we need to know them by name?
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