CHEM125 – CHAPTER 09 – BASIC HOMEWORK

CHAPTER 09 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.) Help: Bond types FI

Choose…IonicPurely covalentPolar covalent chem125-8r1 - Fluff Butt ReviewsCsI

Choose…IonicPurely covalentPolar covalent chem125-8r1 - Fluff Butt ReviewsH2

Choose…IonicPurely covalentPolar covalent chem125-8r1 - Fluff Butt Reviews

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? Help: Electronegativity difference examples Answer: chem125-8r1 - Fluff Butt Reviews

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? Help: Electronegativity and bond polarity chem125-8r1 - Fluff Butt Reviews

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? Help: Lattice energy Select one: chem125-8r1 - Fluff Butt Reviews

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 CHEM125 - CHAPTER 09 - BASIC HOMEWORK 1 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: chem125-8r1 - Fluff Butt Reviews

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. CHEM125 - CHAPTER 09 - BASIC HOMEWORK 1 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? Help: Valence electrons

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:  chem125-8r1 - Fluff Butt Reviews

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: chem125-8r1 - Fluff Butt Reviews

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: chem125-8r1 - Fluff Butt Reviews chem125-8r1 - Fluff Butt Reviews chem125-8r1 - Fluff Butt Reviews

Explanation

O is the central atomH2O : ( 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: chem125-8r1 - Fluff Butt Reviews chem125-8r1 - Fluff Butt Reviews chem125-8r1 - Fluff Butt Reviews

Explanation

CHEM125 - CHAPTER 09 - BASIC HOMEWORK 3

Question 18

Write the Lewis structure for SiBr4 and check those statements which are correct. Select one or more: chem125-8r1 - Fluff Butt Reviews chem125-8r1 - Fluff Butt Reviews chem125-8r1 - Fluff Butt Reviews

Explanation

CHEM125 - CHAPTER 09 - BASIC HOMEWORK 4

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: chem125-8r1 - Fluff Butt Reviews chem125-8r1 - Fluff Butt Reviews chem125-8r1 - Fluff Butt Reviews

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

CHEM125 - CHAPTER 09 - BASIC HOMEWORK 5

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.

Help: Oxygen

Select one or more: chem125-8r1 - Fluff Butt Reviews chem125-8r1 - Fluff Butt Reviews chem125-8r1 - Fluff Butt Reviews

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: chem125-8r1 - Fluff Butt Reviews chem125-8r1 - Fluff Butt Reviews chem125-8r1 - Fluff Butt Reviews chem125-8r1 - Fluff Butt Reviews

Explanation

CHEM125 - CHAPTER 09 - BASIC HOMEWORK 6

  •  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: chem125-8r1 - Fluff Butt Reviews chem125-8r1 - Fluff Butt Reviews chem125-8r1 - Fluff Butt Reviews chem125-8r1 - Fluff Butt Reviews

Explanation

CHEM125 - CHAPTER 09 - BASIC HOMEWORK 7

  • 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: chem125-8r1 - Fluff Butt Reviews chem125-8r1 - Fluff Butt Reviews chem125-8r1 - Fluff Butt Reviews chem125-8r1 - Fluff Butt Reviews

Explanation

CHEM125 - CHAPTER 09 - BASIC HOMEWORK 8

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

CHEM125 - CHAPTER 09 - BASIC HOMEWORK 9 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: chem125-8r1 - Fluff Butt Reviews chem125-8r1 - Fluff Butt Reviews chem125-8r1 - Fluff Butt Reviews

Explanation

CHEM125 - CHAPTER 09 - BASIC HOMEWORK 10 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: chem125-8r1 - Fluff Butt Reviews chem125-8r1 - Fluff Butt Reviews

Explanation

CHEM125 - CHAPTER 09 - BASIC HOMEWORK 11 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: chem125-8r1 - Fluff Butt Reviews chem125-8r1 - Fluff Butt Reviews chem125-8r1 - Fluff Butt Reviews

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: chem125-8r1 - Fluff Butt Reviews

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. chem125-8r1 - Fluff Butt Reviews

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

chem125-8r1 - Fluff Butt Reviews

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? chem125-8r1 - Fluff Butt Reviews

Explanation

CHEM125 - CHAPTER 09 - BASIC HOMEWORK 12 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)