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CHAPTER 9 BASIC HOMEWORK

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Question 1

Match the molecule with the kind of bond which is made. (All answers must be correct for credit.) 

FI Correct
CsI Correct
H2 Correct

 

Explanation

FI = 4.0 - 2.6 = 1.4 (polar covalent)

CsI = 0.7 - 2.7 = 2.0 (ionic)

H2 = 2.1 - 2.1 = 0 (pure covalent

 

Question 2

What is the difference in electronegativity for the most ionic of the following compounds: CsCl, MgF2, FI, and NH3

Answer: Correct

 

Explanation

CsCl: 0.7 - 3.0 = 2.3


MgF2 : 1.2 - 4.0 = 2.8


FI : 4.0 - 2.5 = 1.5


NH3 :  0.9 - 2.1 = 1.2

 

 

Question 3

What is the difference in electronegativity between the atoms in HI? 


Correct

 

Explanation

 HI : 2.1 - 2.5 =  0.4

 

Question 4

Which of the atoms in HI has a partial positive charge? Namely, when HI is placed in the electric field between two charged plates, which atom would point towards the negative plate? Write either H or I

 

Explanation

 I is more electronegative than H, which means that I is polarized with negative charge. Therefore, H has to be positively charged. If H is positive than it attracted to the negative plate.

 

Question 5

Which of the following ionic compounds has the highest melting point? 

Select one:
 Correct

 

Explanation

The molecule with the smallest radius of elements (means they share have a strong bond) and highest total charge is the ionic compound with the highest melting point.


Be O : (+2) ( - 2) = -4

radius: Be has smaller radius than Sr


This formula is used to determine the strength of the bond. The stronger the force the higher the melting point.  

 

Question 6

Which of the following ionic compounds has the lowest melting point?

Select one:
 Correct

 

Explanation

 The molecule with the biggest radius of elements (means they share have a weaker bond) and smallest total charge is the ionic compound with the lowest melting point.

This formula is used to determine the strength of the bond. The weaker the force the lower the melting point. 

 

Question 7

How many valence electrons does boron have? 

 

Explanation

 

[He] 2s2 2p1

Count the electrons on the highest n energy level only
 

Question 8

How many valence electrons does magnesium have?

 

Explanation

 

[Ne] 3s2

Count the electrons on the highest n energy level only
 

Question 9

How many valence electrons does bromine have?

 

Explanation

 

[Ar] 3d10 4s2 4p5

Count the electron on the highest n energy level only
 

Question 10

How many valence electrons does argon have?

 

Explanation

 

[Ne] 3s2 3p6

Count the electron on the highest n energy level only
 

Question 11

Which letters (a, b, c, d, e, f, g, or h) shows the correct Lewis structure for the following:  O, S, Kr, Ga? Give answer as 4 letters separated by a comma and a space. Example: a, a, a, a.

Answer: 

Correct

 

Explanation

How to create Lewis Structure

  1. Count the number of valence electrons. The number of valence electrons are determined by the group number on top of periodic table.
  2. Place the valence electrons in pairs around the element

 

Question 15

Which of the following statements about Lewis Structures is FALSE?

Help: Octet rule

Select one:
 Correct

 

Explanation

Carbon can make only 4 bonds.

 

Question 16

Write the Lewis structure for H2O and check those statements which are correct.

Help: Determining Lewis structures

Select one or more:
 Correct
 Correct
 Correct

 

Explanation

 

 

O is the central atom
H2O : ( 2 x 1) + 6 = 8
 
 

Question 17

Write the Lewis structure for NH41+ and check those statements which are correct.

Help: Lewis structure ions

Select one or more:
 Correct
 Correct
 Correct

 

Explanation

 

Question 18

Write the Lewis structure for SiBr4 and check those statements which are correct.

Select one or more:
 Correct
 Correct
 Correct

 

Explanation

 

 

Question 19

Which bonding structure (lone pairs of electrons not shown) correctly represents hydroxylamine, NH3O? Also, check those statements which are correct for the completed Lewis structure. 

  


Select one or more:
 Correct
 Correct
 Correct

 

Explanation

Left Structure: oxygen has -1 charge making overall charge -1

Right Structure: all element have 0 charge making overall charge 0  corresponds to the overall charge of the formula NH3O. (best choice)


  • N has 1 lone pair of electron
  •  O has 2 lone pairs of electrons

 

Question 20

Which bonding structure (lone pairs of electrons not shown) correctly represents phosphorous acid, H3PO3? Also, check those statements which are correct for the completed Lewis structure satisfying the octet rule.

Select one or more:
 Correct
 Correct
 Correct

 

Explanation

Complete structure

  • 26 valence electrons
  • P has 1 lone pair

 

Question 21

Formaldehyde, H2CO, is a gas with a characteristic pungent odor. Draw its Lewis structure. Which statements are correct regarding its Lewis structure?

Help: Multiple bonds and octet rule


Select one or more:
 Correct
 Correct
 Correct
 Correct

 

Explanation

 

 
 

  •  There are 12 valence electrons.
  • The C-O bond is a double bond
  • C has no lone pair of electrons.
  •  
 

Question 22

Draw the Lewis structure for hydogen cyanide, HCN. Which statements are correct regarding its Lewis structure?

Select one or more:
 Correct
 Correct
 Correct
 Correct

 

Explanation

  • There are 10 valence electrons
  • C-N has a triple bond
  • C has  0 lone pairs
  • N has 1 lone pair
 

Question 23

Draw the Lewis structures for the carbonate ion, CO32-. Which statements are correct regarding its Lewis structures?

Help: Resonance structures

Select one or more:
 Correct
 Correct
 Correct
 Correct

 

Explanation

 

 

Question 24

What is the steric number for the O atom in water? Draw the Lewis formula for water before answering the question. 

Help: Steric number


 

Explanation

 Steric Number: number of lone pairs + number of bonds (single, double, triple bonds are counted as one) 

 
 
Oxygen Steric Number: 

2 lone pairs + 2 bonds = 4

 

Question 25

What is the steric number for either N in N2? Draw the Lewis formula before answering the question.

 

Explanation

 
 

Nitrogen Steric Number


1 lone pair + 1 bond = 2

 

Question 26

Draw the Lewis structure for the PCl5. Which statements are correct regarding its Lewis structure?

Help: Exceptions to octet rule

Select one or more:
 Correct
 Correct
 Correct

 

Explanation

P Cl :  5 + (5 x 7) = 40 valence electrons

P : 5 bonds + 0 lone pairs = 5 

octet rule is not obeyed because more than 8 electrons are shared by P

 

Question 27

Draw the Lewis structure for I3-. Which statements are correct regarding its Lewis structure? (Note, one of the I is the central atom and the other 2 are bonded to it.)

Select one or more:
 Correct
 Correct

 

Explanation

I3-  : ( 3 x 7 ) + 1 = 22

 

Question 28

Draw the Lewis structure for the iodine dioxide difluoride ion, IO2F2-. Which statements are correct regarding its Lewis structure? (Note, all the atoms are bonded to the central I atom.)

Select one or more:
 Correct
 Correct
 Correct

 

Explanation

 
 

IO2F2-  :  7 + (6 x 2) + (7 x 2) + 1 = 34 valence electrons


I = 5 bonds + 0 lone pair = 5 steric number

 

 

Question 29

Arrange the following diatomic molecules in order of weakest to strongest bond: HF, HCl, HBr, and HI. Write your answer with or without commas and do not include the "and". For example, alphabetically, you would write: HBr, HCl, HF, HI or HBr HCl HF HI.

Aside, do you notice a pattern?

Answer: Correct

 

Explanation

 H - Br : 368 kJ/mol


HCl: 431 kJ/mol


HF: 569 kJ/mol


HI: 297 kJ/mol


lowest to highest

HI HBr HCl HF

 

Question 30

What is the average difference in bond energy in kJ/mol between the double bond in the O2 molecule and a single O-O bond, such as in hydrogen peroxide (H2O2)? Report as a positive quantity.

Correct

 

Explanation

 O2 : 498 kJ/mol

 O-O: 146 kJ/ mol


498 kJ/mol - 146 kJ/mol = 352kJ/ mol

 

Question 31

What energy in kJ is required to break 3.31 mol of NH3 into atoms? As noted below, this information can be used to calculate ΔH for gas-phase reactions.

Help: Energy to break bonds


Correct

 

Explanation

3 x N-H =1167 kJ/ mol


3.31 mol x 1167 kJ/ mol = 3862.77 kJ

 

 

Question 32

What is the approximate ΔH in kJ for the following reaction as written:

2NH3(g) --> 3H2(g) + N2(g) 

Careful, what kind of bond does the nitrogen molecule make?


Correct

 

Explanation

Bond Enthalpies: 
ΔH = H(products) - H(reactants) 
ΔH = [(3*436) + 946] - 2*[3*389] 
ΔH = -80 J/mol 

It should be positive because it is endothermic reaction and bonds are being broken to single elements.

so... ΔH = 80 J/mol

Nitrogen makes a triple bond with itself, therefore, use that value (N≡N ~ 946 kJ/mol)


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