Exam 3 Preceptor Review

Exam 3 Preceptor Review - LewisDotStructures&...

Info iconThis preview shows pages 1–22. Sign up to view the full content.

View Full Document Right Arrow Icon
 2/6/11 Lewis Dot Structures & Formal Charges Amanda & Caroline
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
 2/6/11 Formal Charge:  formal charge  (FC) is the charge  assigned to an atom in a molecule, assuming that  electrons in a chemical bond are shared equally  between atoms, regardless of relative  electronegativity. The structure preferred is usually the one that has  overall the lowest formal charge Formal Charge Review 
Background image of page 2
 2/6/11 Formal Charge= (Valence Electrons)-[Number of  Covalent bonds]-[number of electrons in lone  pairs]
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
 2/6/11 Formal Charge Example O-O=O 6-5=+1 6-6=0 6-7=-1 Valence electrons from group number on periodic table Total formal charge -1 + 1 + 0 = 0
Background image of page 4
 2/6/11 Decide the total # of electrons needed for the structure After the # of electrons are identified, decide which should be the central atom. The most electropositive is made the central atom. Use formal charge to decide which structure is best Hint: Not always but it is common to find these following central atoms with more than eight electrons: P,S,I, & Xe ( any atom beyond Ne) How to Draw a Lewis Dot 
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
 2/6/11 Examples NH3 BrF3 N2 H2CO
Background image of page 6
 2/6/11
Background image of page 7

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
 2/6/11 Answers
Background image of page 8
 2/6/11 NH3 = 5-3-2 =0 BrF3 Br= 7-3-4 =0 F =7-1-6=0 N2 = 5-3-2=0 H2CO C= 4-4-0=0 O=6-2-4=0 Answer for the Formal Charges 
Background image of page 9

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
 2/6/11 BCl3 HCN CCl3COOH More examples 
Background image of page 10
 2/6/11
Background image of page 11

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
 2/6/11 3(7) + 3 = 24 e- total Place remaining electrons, in pairs, around  appropriate atoms; start with outer atoms. 24 - 6 = 18 e- left; therefore 9 lone pairs to add: -Make sure all atoms that need octets have octets:  The Cl’s have octets, so they’re okay; B is special element that can have an incomplete  octe t, so B only needs 6. We’re done here.
Background image of page 12
 2/6/11 N = 5 – 3 - 2 = 0 C = 4 – 4 = 0 H = 1 – 1 = 0
Background image of page 13

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
 2/6/11 C= 4-4= 0 Cl=7-6-1=0 O=6-4-2=0 O= 6-4-2=0
Background image of page 14
 2/6/11 Resonance   When more than one Lewis structure can be drawn,  the molecule or ion is said to have resonance Hint: When drawing resonance structures, use this  format: [ ] [ ] [ ]
Background image of page 15

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
 2/6/11 Examples O3 CO3 2- NO3 -
Background image of page 16
 2/6/11 Nitrate and carbonate are pretty similar.  How  about  CH3COO-   and compare that to  CH3COOH that has no resonance. C2O4 2- has a pile of resonance.
Background image of page 17

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
 2/6/11 O 3 NO 3 -
Background image of page 18
 2/6/11 O3 (left to right) O1=6-1-6=-1 O2= 6-3-2=1 O3=6-2-4=0 CO3 2- O1=6-1-6=-1 O2= 6-1-6=-1 O3=6-2-4=0 -1+-1+0+0= -2 C= 4-4-0=0 Answers
Background image of page 19

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
 2/6/11 NO3 – O1=6-2-4=0 O2= 6-1-6=-1 O3=6-1-6=-1 0+(-1)+(-1)+1=-1 N=5-4-0=1
Background image of page 20
Background image of page 21

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 22
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 79

Exam 3 Preceptor Review - LewisDotStructures&...

This preview shows document pages 1 - 22. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online