drawing lewis structures and vsepr a tutorial on writing lewis dot structure
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Drawing Lewis Structures and VSEPR A Tutorial on Writing Lewis Dot Structure
Drawing Lewis Structures and VSEPR A Tutorial on Writing Lewis Dot Structure
OCTET RULE:• atoms will gain, lose or share electrons to fill their
valence shell (noble gas)
• use only valence electrons in drawing Lewis dot.
STEPS / RULES TO LEWIS DOT:
• Determine total valence electrons for all atoms. ~Watch for negative/positive/polyatomic ions.
• Position least electronegative atom in the centre.~central atom usually first in formula (unless H/ F).
CH2ClF, SeCl2, O3 (CO2, NH3, PO43-)
• Write other atoms around central with line bond.~line represents 2 e- (must be subtracted from total)
Se – ClCl –
• Place electrons around each atom to fill valence.
• Too few electrons - give each atom a complete octet by adding double or triple bonds.
SeCl2 : 6 +7 + 7 = 20 - 4
Se – ClCl –
Draw the Lewis structure for CO2:
CO2 : 4 + 6 + 6 = 16
C – OO –
- 4
– –
S – OO ––
O– O
Draw the Lewis structure for SO42- :
SO42- : 6 + (4)6 + 2 = 32 - 8
2-
BeCl2 : 2 + 7 + 7 = 16
– ClCl –
Be
- 4
Ionic Bond
-1
Cl
+2
Be
-1
Cl
VSEPRValence Shell Electron Pair Repulsion Theory
• Predicts 3D structures of molecules.
• Shape calculated by comparing bonding and lone
pair electrons around the central atom.
• Minimizes the electrostatic repulsion between electrons in valence sublevels.
AXE method:
A: Central atomXn: # of bonding pairsEn: # lone pairs
Draw the Lewis structure for BF3:BF3 : 3 + (3)7 = 24
- 6
– FF – B
F
–
*Unusual(Does not have octet)
3 – bonding pairs (X3)0 – lone pairs
Trigonal Planar– 120o bond angle
Central Atom with only bonding pairs:
Draw the Lewis structure for CH4:
Draw the Lewis structure for PCl5:
Draw the Lewis structure for SF6:
4 – bonding pairs (X4)0 – lone pairs
Tetrahedral – 109.5o
5 – bonding pairs (X5)0 – lone pairs
Trigonal Bipyramidal – 90o and 120o
6 – bonding pairs (X6)0 – lone pairs
Octahedral – 90o
Central Atom with LONE pairs:Lone pairs have a greater repulsion force and distort the predicted bond angles.
H2S : 1 + 1 + 6 = 8
– HH –
S
- 4
2 – bonding pairs (X2)2 – lone pairs (E2)
Bent – 104.5o bond angle
*Predict Linear
Draw the Lewis structure for PF3:
PF3 : 5 + (3)7 = 26
- 6
– FF – P
F
–
*Predict Trigonal Planar
3 – bonding pairs (X3)1 – lone pairs
Trigonal Pyramidal – 107o
Treat double/triple bonds as single bonds:
CO2 : 4 + 6 + 6 = 16 - 2
Double Bonds
2 – bonding pairs (X2)0 – lone pairs
Linear – 180o bond angle
C – OO –
– –
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