adizzle87

10+ Year Member
Jan 26, 2008
844
2
Status
Dental Student
I have a hard time figuring out the structures of molecules...mainly because I have no idea how many lone pairs there are in molecules..

H2O is bent, NH3 is pyramidal, and CH4 is tetrahedral because those

But with transition metals and noble gasses how do you figure out how many lone pairs there are? For example PCl5...how does one figure out how many lone pairs for that? And for noble gas complexes, anyone know how to figure those out?
 

sciencegod

Super Member
10+ Year Member
Nov 20, 2008
198
0
Status
Pre-Dental
you gotta do the lewis dot structures.
 

5HTburb

10+ Year Member
Dec 24, 2008
30
0
Minneapolis, MN
Status
Dental Student
Some transitions and metalloid (sp?) elements have the possibility of expanding their d-orbitals. Go back through notes and study materials (chemical characteristics of these elements, as well as atomic and molecular orbitals). Really wrapping your head around this subject topic will really help as you continue to study. Good Luck
 
About the Ads

doc3232

10+ Year Member
7+ Year Member
Feb 15, 2008
3,809
10
Status
Dental Student
You really need to UNDERSTAND this stuff. Now just understand it.
Count the electrons, Cl has 7, P has 5.
5 x 7 + 5 = 40.
Because halogens always take 1 electron from the central atom and use their own 7 to make a total of 8, then we know there are no electrons left. Hence, no electron pairs.
 

Danny289

Member
10+ Year Member
Dec 2, 2006
1,523
4
Status
Pre-Dental
I have a hard time figuring out the structures of molecules...mainly because I have no idea how many lone pairs there are in molecules..

H2O is bent, NH3 is pyramidal, and CH4 is tetrahedral because those

But with transition metals and noble gasses how do you figure out how many lone pairs there are? For example PCl5...how does one figure out how many lone pairs for that? And for noble gas complexes, anyone know how to figure those out?
for qiuck respond to these kind of question find the "centeral" atom for example in your question will be "O", "N" and "C"( usually the less number of atom). in next step just put the last layer electron around your central atom.
for example for "O" you are going to have 6 electrons (2 pair electrons and two single electron ) and two hydogen will be bond to to two single electron you are going to have to single bond to hydrogyn and two pair electron that makes binding shape.
for NH3 you will have 5 electron around N ( one pair and 3 singles) those three single will bond to three hydrogyn, you will have 3 single bonds with one pair and(107.5 degree and ....
for PCl5 "P" is centeral atom with 5 electrons as "N" now you have five Cl bonding to five electrons( in this case you are not going to have any electron left not single not pair)
be carefull about double bonds for instance CO2: C is going to be your centeral atom then you will have two double bonds between C and O and linear(180 degree sp hyb.) for these kind of question focus on centeral atom.
hope it helped :)
 

adizzle87

10+ Year Member
Jan 26, 2008
844
2
Status
Dental Student
Thanks guys, really appreciate it. Just drew out the figure and everything made sense, even for that lousy noble gas Radon haha
 
About the Ads