Name: __________ANSWER KEY_______________ Date: ____________________________ Period: ______
Unit 7 Quiz Study Guide – Lewis Structures, Polarity & VSEPR
Draw the lewis dot diagram for the following elements:
1) Na
2) Cl
3) He
4) P
5) Se
6) What are the steps for drawing a Lewis Structure?
1. Count up valence electrons – SHOW WORK
2. Determine Central Atom – C, singular/alone, more electronegativity
3. Bond terminal atoms
4. Recount
5. Fill in lone pairs outside first
6. Check if happy (STABLE OCTET. Only H, He, and B don’t need 8. Everyone else
NEEDS 8.)
7) Define polarity: unequal sharing of electrons in a polar bond. Polar molecules have an overall
dipole. They are not symmetrical and they “move” (horse and cart analogy)
8) Define electronegativity: Atoms desire to get electrons. Fluorine is the most electronegative.
For each of the following pairs of molecules, draw the lewis structure. Then, determine which is most
polar and explain your reason for making this choice:
9) carbon disulfide (CS2)
OR
sulfur difluoride (SF2)
Both are nonpolar!
10) nitrogen trichloride (NCl3)
OR
oxygen dichloride (OCl2)
Nitrogen trichloride because it is not symmetrical and “would move”
11) boron trihydride (BH3)
OR
ammonia (NH3)
Ammonia (BH3 is symmetrical – trigonal planar)
12) chlorine (Cl2)
OR
phosphorus trichloride (PCl3)
Phosphorous trichloride is polar. Cl2 is symmetrical.
13) silicon tetrabromide (SiBr4)
OR
HCN
HCN is polar, SiBr4 is symmetrical and therefore nonpolar.
14) Draw all of the reasonable resonance structures and the resonance hybrid for the carbonate
ion, CO3 2–
resonance is all the possible arrangements
15) Which element(s) can have fewer than 8 and still be stable/happy? _H__
__He_
__B__
16) Which element can have more? _P__
17) What does VSEPR stand for? Valence shell electron pair repulsion
18) What is VSEPR Theory used for? Determining 3D shapes of molecules
19) The molecular geometry of the H3O+ ion is _trigonal pyramid_. (Remember: Draw Lewis
structure first)
20) The bond angle around the central atom in SO2 is ___. Skip this question
21) The central atom in PCl5 has __0__ lone pairs and __5_ bonded atoms. So its molecular
geometry is _trigonal bipyramid_ and its bond angle is _90/120__.
22) Complete the table below
Formula
Lewis Structure
Shape (Geometry)
Polar or Nonpolar?
HF
Linear
Polar
CO2
Linear
Nonpolar
H2O
Bent
Polar
CCl4
Tetrahedral
Nonpolar
NH4 +
Tetrahedral
Nonpolar
23) How many electrons are shared in a double bond? __4_ A triple bond? _6__
24) Element X has three bonded atoms, and 0 lone pairs. What is its molecular geometry
according to VSEPR? __trigonal planar____
25) Element Y has 4 bonded atoms and 2 lone pairs. What is its molecular shape according to
VSPER? __square planar___