Molecular Polarity

Dipole moments or polarity happen in molecules when there is an unequal sharing of electrons. 

Molecular Polarity

Concept: Understanding Molecular Polarity 

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Video Transcript

We're going to say molecules that have unequal sharing of electrons contain a molecular polarity. Why do they have unequal sharing? They have unequal sharing because one element will be more electronegative than the other elements. That element that is more electronegative will hoard or take in all the electron in for itself making it more partially negative. The other elements as a result will become more partially positive. What we're going to say here is to do this, we're going to have basic rules we have to follow. We’re going to say in these molecules, the reason that they're polar is because of their shape and also because of bond polarity.
Recall, just the shape and the bond polarity will affect the whole polarity of the molecule. This has to do with some of the concepts we learned about electronegativity and also some of the concepts we learned about dipole arrows. These are going to come into play when we're trying to figure out the polarity a molecule. 

Both a molecule's shape and bond polarity can affect its overall polarity. 

Concept: The First Rule for Molecular Polarity

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Video Transcript

We break it down into two simple rules. These are the rules to determine if a compound will be nonpolar. If it follows all the rules, it's going to be nonpolar. If it breaks any of them, it’s going to automatically be polar.
We're going to say for molecular compounds where the central element has no lone pairs, no lone pairs at all, we're going to follow two rules. We’re going to say first the central element must be connected to the same elements. That's rule number one. If it breaks that, it’s automatically polar. Then second rules, the central element must be less electronegative than the surrounding elements. If it breaks this rule, it's automatically polar. You have to follow both rules in order to be nonpolar.
Let me give you a quick example before I let you guys do this one as practice. We could have CCl4. We’d say the central element has the same elements all around so it follows rule 1A. Then we’re going to say the central element carbon is less electronegative than the chlorines around it. Therefore, this follows both rules, so therefore it’s nonpolar.
But let’s say I did carbon in the center and I do this instead. Now we're going to say that the central element doesn't have all the same groups around it so it breaks rule 1A and automatically, since it breaks any of the rules, it's going to be polar. This is the approach you have to take.

When the central element has no lone pairs and has the same surrounding elements then usually the molecule is nonpolar. 

Problem: Determine if carbon dioxide, CO2, is polar or nonpolar.

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Example: Determine if silicon tetrachloride, SiCl4, is polar or nonpolar. 

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Concept: The Second Rule for Molecular Polarity

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Video Transcript

Welcome back, guys! We're now going to continue our discussion on polarity when our central element has lone pairs. It sucks when our central element has lone pairs because we have more rules we have to follow. Let's take a look. We're going to say when our central element does have lone pairs, the central element must be connected to the same elements. We're also going to say that the central element must be less electronegative than the surrounding elements. Those two rules stay the same whether we have lone pairs or we don't.
Here's the new part. We're going to say use dipole arrows to point to the more electronegative element. These dipole arrows must cancel out. Remember, we talked about dipole arrows a few videos back. For them to cancel out, they have to go in opposite directions. If they go inward, they don't cancel out. They actually make the molecule more polar, make the bonds more polar.
We're also going to say that we also have dipole arrows for lone pairs. We're going to say dipole arrows extend away from lone pairs. These long pier dipole arrows must also cancel out. We need to make a distinction here. We have two types of dipole arrows. We have dipole arrows between elements and we have dipole arrows between lone pairs. They cannot cancel each other out. Lone pair dipole arrows must cancel out lone pair dipole arrows. Element dipole arrows must cancel out element dipole arrows.
Before I let you do this one, let's look at an example together. Let's say we have to draw NH3. NH3 is nitrogen in the center and we have the hydrogens connected to it. See our central element has lone pairs, so we use the rules. The central element must be connected to the same elements, which it is. But it breaks rule 2B. The central element is more electronegative. Since it breaks rule 2B, this is automatically polar. You would say that this compound here is automatically polar.
Let's take a look at another example. Here we're going to say, let’s see. We have Sn, or actually we’ll have OF2. OF2 would look like this. First rule, we’re going to say central element must be connected to the same elements all the way around, which it is. Center element must be less electronegative than the surrounding elements, which it is. We have to use dipole arrows for pat C and D. We're going to say use dipole arrows to point to the more electronegative element. The way we do this is we look at the oxygen. Here's our oxygen. We’re looking between this oxygen here and this fluorine here. We're going to draw a dipole arrow between the two. Whoever is more electronegative between the two, we point the dipole arrow towards them. Fluorine is more electronegative so we point a dipole arrow towards it.
Now we’re going to look again at the oxygen and the other fluorine. Again, the dipole arrow will point towards the more electronegative element, that fluorine. We’re going to say that these two dipole arrows, element dipole arrows, are pointing in opposite directions. They're going to cancel each other out. Part C is followed as well.
Now we have to go to Part D. For Part D, lone pairs also have their own dipoles. We're going to have a dipole arrow extending away from this lone pair and away from this lone pair. We're going to say that both those dipole arrows are pointing in opposite directions away from each other. Because they're pointing away from each other, they're going to cancel each other out. Part D is also followed. Using Part A, B, C and D, you see that we follow every single rule. Therefore, we’ll say that this is nonpolar. That’s the steps that you have to take when answering these types of questions.
I want you guys to take the same approach when you draw xenon tetrafluoride. Draw it out first. See if it has lone pairs. Use the rules from A to D to see what the correct answer would be. Once you do that, click on the explanation button and see what we do to figure out if it’s polar or nonpolar.

When the central element has lone pairs then we must use element dipole arrows and lone pair dipole arrows to determine polarity. 

Problem: Determine if xenon tetrafluoride is polar or nonpolar.

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Example: Determine if phosphorus trihydride, PH3, is polar or nonpolar. 

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Problem: Determine if the following compound is polar or nonpolar. SiBr42-

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Problem: Determine if the following compound is polar or nonpolar. H2S

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Problem: Determine if the following compound is polar or nonpolar. PCl2F3

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Problem: Determine if the following compound is polar or nonpolar. IF2-

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Molecular Polarity Additional Practice Problems

How can one nonpolar molecule induce a dipole in a nearby nonpolar molecule?

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Distinguish between polarizability and polarity. How does each influence intermolecular forces?

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How do you determine if a molecule is polar or nonpolar?

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There are 3 different possible isomers of a dibromoethene molecule, C 2H2Br2. One of them has no net dipole moment, but the other two do. Draw Lewis structures for each of these isomers. Include H atoms.

Nonpolar C2H2Br2 (one isomer)

Polar C2H2Br(two isomers)

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Which of the following molecules is nonpolar?

a. NH3
b. OF2
c. CH3Cl
d. H2O
e. BeCl

 

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Which of the following compounds are polar:

a. CBr4, XeF2, SCl4, BrF3, CH3OH

b. XeF2, SCl4, BrF3, CH3OH only

c. BrF3, CH3OH only 

d. SCl4, BrF3, CH3OH only


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Identify the molecules with polar bonds and the polar molecules.

a. CCl4 
b. CH3Cl
c. H2O
d. CO2
e. O2

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Which of the following molecules is not necessarily polar?

a. SeF4

b. SO2

c. CH2Cl2

d. PH3

e. Cl2XeF2

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Is ICl4- polar or nonpolar?

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a) PF3Cl2 is a nonpolar molecule. Based on this information, determine the F−P−F bond angle, the Cl−P−Cl bond angle, and the F−P−Cl bond angle. 



b) Which statement best describes the polarity of CF2Cl2?

a. The molecule is always polar.

b. The molecule is always nonpolar.

c. Depending on the arrangement of outer atoms, this molecule could be polar or nonpolar.

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Choose from the compound below that contains at least one polar covalent bond, but is non-polar.

a. HCN

b. CF4

c. SeBr4

d. ICl3

e. Both B and C are non-polar and contain a polar covalent bond

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Predict whether each of the following molecules is polar or non-polar:

IF, CS2, SO3, PCl3, SF6, IF5

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Predict whether each of the following molecules is polar or nonpolar.

XeF4, NH3, CH3Br, CCl4, SF4, GaH3

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Water is known as a polar molecule because (check all apply)

a. The oxygen and hydrogen atoms have the same electronegativity.

b. The hydrogen atom attracts electrons much more strongly than the oxygen atom.

c. Water has two hydrogen atoms covalently bonded to a single oxygen atom.

d. The oxygen atom has a greater attraction for electrons than the hydrogen atom does.

e. Water dipole moment is equal to zero.

f. The electrons of the covalent bond are not shared equally between the hydrogen and oxygen atoms.

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Determine whether each molecule is polar or nonpolar. Drag the appropriate items to their respective bins.

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Identify whether each molecule given below is polar or nonpolar.

SiH3Br, SBr2, BrF3, BF3

 

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Determine whether each molecule given below is polar or nonpolar.

CF4, PBr5, XeF2, SF  

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Determine whether each molecule given below is polar or nonpolar:

NF3, XeF2, H2S, and CF4.

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Explain whether Cl2XeF2 is necessarily polar?

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Consider the molecule IF3.

i) What is the electron domain geometry and the molecular geometry of IF 3?

ii) Is IF3 polar or nonpolar?

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Is SCl4 polar or non polar?

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Draw the Lewis structure for the CH 2Br2.

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Is CS2 polar or nonpolar?

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Are SO3,XeF2,IF2- polar or nonpolar? How it is polar or nonpolar? Add formal charges and bond dipoles to all lewis dot structures. 

According to Vallence bond theory , what is the hybridization of all atoms in SO 3? Describe the orbitals that overlap to form all bonds in SO3.

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Is HBr a polar or non polar molecule?

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Is ClF3 polar or non polar?

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Is O3 polar or non-polar?

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Predict which molecules are polar. Select all that apply.

a) AsF3

b) IOF5

c) CF4

d) CH2Cl2

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Classify these molecules as polar or nonpolar.

CH3Cl

CCl4

HF

BCl3

H2O

H2

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BrCl5 (bromine pentachloride) is sometimes called a polar molecule, sometimes called nonpolar. Which one is it REALLY and WHY?

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Is XeF4 polar or nonpolar? Explain your answer.

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Is BeCl2 polar or nonpolar?

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Is XeF2 polar or nonpolar?

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Is H2O polar or nonpolar?

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Why is CCl4 non-polar and SF4 polar?

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Is the CH4 a polar or non-polar bond? What about the molecule as a whole? Is that molecule CH4 a polar or non-polar?

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Draw the lewis dot structure for CH 2Cl2. Is this molecule polar?

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Rank the following molecules from the least polar to the most polar:

CH2Br2, CF2Cl2, CH2F2, CH2Cl2, CBr4, CF2Br2.

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Which of these molecules are polar? Check all that apply

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Which statement is true about the polarity of HCN, which has a structure of H-C≡N:?

(Hint: The electronegativities of H, C, and N are 2.1, 2.5, and 3.0, respectively.)

a. The carbon-nitrogen bond in HCN is a polar-covalent bond

b. Both bonds in HCN are nonpolar covalent bonds

c. The total molecular dipole moment in HCN points towards the H atom

d. Statements a and c are correct

e. Statements b and c are correct

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Consider the following molecules

I. BCl3        II. CHBr3 (C is the central atom)      III. Cl2        IV. XeBr2          V. CO

These molecules have a zero net dipole moment (nonplolar)

  1. III, V
  2. III, IV, V
  3. I, III, IV
  4. I, III, IV, VI
  5. None of them 
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Consider four molecules
I) CHCl3
II) CH4
III) CH3Cl
IV) CCl4

Which of these exhibit permanent dipole-dipole interactions?

1. I only

2. III only

3. I and III only

4. None of these

5. I, III, and IV only

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Which of the following will be dissolved in water?

NH3, CF4, CO2

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Specify the polarity of the bonds and the overall polarity of the molecule.

# of Polar Bonds _____________

Polar molecule (yes/no) _______________

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Specify the polarity of the bonds and the overall polarity of the molecule.

# of Polar Bonds _____________

Polar molecule (yes/no) _______________

 

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Select the molecule that is the most polar
a. PCI5
b. BrCl5
c. XeF4
d. CCl4
e. XeF2

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Explain why CO2 is nonpolar, but OCS is polar?

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In which of the following liquids is iodine (I 2) expected to be most soluble?

A) CH2Cl2

B) H2O

C) Methanol

D) Ethanol

E) CCl4

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Which of the following compounds should be soluble in CCI 4?

A. NaCl
B. C8H18
C. H2O
D. NH3
E. None of these compounds is soluble in CCI4

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Coca-Cola took a public relations hit a few months ago when it was discovered that their “scientists” stated that obesity was due to insufficient exercise and not sugary soft drinks (New York Times, August 9, 2015).

Why is sugar so soluble in water?

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Classify the molecule AsCl3.

1. polar molecule with polar bonds

2. polar molecule with nonpolar bonds

3. nonpolar molecule with nonpolar bonds

4. nonpolar molecule with polar bonds

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Consider four molecules

I) CHCl3
II) CH4
III) CH3Cl
IV) CCl4

Which of these exhibit permanent dipole-dipole interactions?

1. I, III, and IV only

2. III only

3. None of these

4. I only

5. I and III only

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How many of the following molecules are polar?

CF            PCl  3            H 2S            ICl 5

a. 0

b. 1

c. 2

d. 3

e. 4

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Which of the following molecules is non-polar?

A) XeF4

B) H2O

C) PH3

D) O3

E) H2O2

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Which of these gases can be most efficiently collected by the displacement of water?

a) ammonia

b) carbon dioxide

c) oxygen

d) hydrogen chloride

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Choose the compound below that contains at least one polar covalent bond, but is nonpolar.

A) SCl2

B) CF2Cl2

C) BCl3

D) GeH2Br2

E) All of the above are nonpolar and contain a polar covalent bond.

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Predict which of the following molecules is non-polar.

a) HBr

b) CF4

c) H2S

d) NI3

e) CHCl3

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Which statement best describes the polarity of CF 2I2

a) the molecule is nonpolar because the dipoles of the C—I bonds cancel each other

b) the molecule is nonpolar because the dipoles of the C—F bonds cancel each other

c) depending on the arrangement of the surrounding atoms, the molecule could be polar or nonpolar

d) the molecule is always polar

e) the molecule is always nonpolar

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Which molecule below is nonpolar? 

a) SF4

b) OF2

c) PH3

d) CBrCl3

e) XeCl4

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How would you describe the molecular polarity of SeCl 6?

  1. Nonpolar, because Se-Cl is a nonpolar bond and there is no lone pair on Se
  2. Nonpolar, because Se-Cl is a polar bond but the geometry is symmetric
  3. Polar, because Se-Cl is a polar bond although the geometry is symmetric
  4. Polar, because Se-Cl is a polar bond and there is a lone pair on Se
  5. Polar, because Se-Cl is a nonpolar bond but there is a lone pair on Se
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The molecules below are described as either polar or non-polar. Which one is incorrectly described?

(a) OCN - Polar

(b) CH2Cl2 - Non-polar

(c) CO2 - Non-polar

(d) NH3 - Polar

(e) SO2 - Polar

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Of the molecules drawn below, which is non-polar? If they are all polar, then do not circle a structure. 

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Which one of the following molecules is polar?

a) PBr5

b) CCl4

c) BrF5

d) XeF

e) XeF4

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Which of the following isomers of PF 2Cl3 are polar?

a) only I

b) only II

c) only III

d) II and III

e) I, II, and III

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Complete this sentence:  The PCl 5 molecule has

            A)      nonpolar bonds, and is a nonpolar molecule.

            B)      nonpolar bonds, but is a polar molecule.

            C)      polar bonds, and is a polar molecule.

            D)      coordinate covalent bonds

            E)      polar bonds, but is a nonpolar molecule.

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For the molecules below, provide the Lewis dot structure, draw the three dimensional dash-wedge structure, and comment on the polarity of the molecule.

a. Nitrous acid, HNO2

b. Polypropylene, CH3CHCH2

c. Percholorethylene, CCl2CCl2

d. Sulfonyl fluoride, SO2F2

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Which one of the following is a nonpolar molecule with polar covalent bonds?

a. NH3

b. H2Se

c. SOBr2 (S is central atom)

d. BeCl2

e. HCl

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Which of the following statements about polar molecules is  false?

a. A molecule with polar bonds can be nonpolar.

b. A molecule with polar bonds can be polar.

c. A molecule with only nonpolar bonds can be polar.

d. A molecule with 120° bond angles can be polar.

e. A molecule with 180° bond angles can be polar.

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Which of the following shows these molecules in order from the most polar to least polar?

a. CH4 > CF2Cl2 > CCl4 CCl2H2

b. CH4 > CF2H2 > CF2Cl2 > CCl4 > CCl2H2

c. CF2Cl2 > CF2H2 > CCl2H2 > CH4 = CCl4

d. CF2H2 > CCl2H2 > CF2Cl2 > CH4 = CCl4

e. CF2Cl2 > CF2H2 > CCl4 > CCl2H2 > CH4

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Which statement best describes the polarity of CF 2l2?

a. the molecule is nonpolar because the dipoles of the C-l bonds cancel each other.

b. the molecule is nonpolar because the dipoles of the C-F bonds cancel each other

c. depending on the arrangement of the surrounding atoms, the molecule could be polar or nonpolar

d. the molecule is always polar

e. the molecule is always nonpolar

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Which molecule below is nonpolar?

a. SF4

b. OF2

c. PH3

d. CBrCl3

e. XeCl4

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Which of the following statements about SF5 is true?

1. The ion has polar bonds and the ion is polar.

2. The ion has polar bonds but the ion is nonpolar. 

3. The ion has nonpolar bonds and the ion is nonpolar. 

4. The ion has nonpolar bonds but the ion is polar. 

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Which of the following statements about SO 32- is true?

1. The bonds are polar and the ion is polar.

2. The bonds are polar and the ion is nonpolar.

3. The bonds are nonpolar and the ion is polar.

4. The bonds are nonpolar and the ion is nonpolar.

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Which of the following species is nonpolar?

1. SCl2

2. ClO3-

3. IF2-

4. IF5

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Which of these is nonpolar?

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Which of the following statements concerning polar molecules is false?

a. There must be at least one polar bond or one unshared pair of electrons on the central atom.

b. If there are more than one polar bond, they must not be symmetrically arranged so that their polarities cancel.

c. If there are more than one unshared pair of electrons on the central atom, they must not be symmetrically arranged so that their polarities cancel.

d. There must be an odd number of polar bonds so that their polarities not cancel.

e. A molecule with symmetrically arranged polar bonds can be polar if the central atom is bonded to atoms of different elements.

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