Module 3 DBA/Exam Review - ANSWER KEY 
Chemistry V22; ID 5657 - All hyperlinks are from our Course Help Site
Multiple Choice format questions:

1.	Which of the following atoms has 3 valence electrons?  (3.01)
a.	Aluminum   		c. 	Carbon
b.	Nitrogen		d. 	Xenon
Check out this special periodic table that has the valence electrons.  

2.	There are two atoms: A and B.  Atom A has 7 electrons and atom B has 13 electrons. Which of the following is true? (3.01)
a.	Atom A is more reactive than atom B
b.	Atom B will give up electrons to form bonds
c.	Both atoms will gain electrons to become stable
d.	Neither atom is reactive
The word “atom” indicates that they are neutral: number of electrons = number of protons.  Atom “A” with 7 electrons (and thus 7 protons) is nitrogen, a nonmetal.  Element “B” with 13 electrons is aluminum, a metal.  Metals are more reactive than nonmetals.  Metals will donate electrons and nonmetals accept electrons.  We can also look at their electron configurations (see module 2) to determine this as well.
●	Atom A: 7 electrons   1s22s22p3    Since we have a half-filled valence shell,  nitrogen will gain 3 electrons, forming the N3- ion. 
●	Atom B: 13 electrons  1s22s22p63s23p1     This atom has 3 valence electrons, in two different sublevels (3s and 3p), so aluminum will donate, or lose those 3 electrons, forming the Al3+ ion. 

3.	An atom has an electron configuration of: 1s22s22p63s23p64s2.  Which of the following is not true?  (3.01)
a.	The element is located in group 4
b.	The element is reactive
c.	The element has 2 valence electrons
d.	This element is a metal
Note: Please review module 2, for writing electron configurations.  Here is a shortcut using the periodic table.  The valence shell is the highest value of “n”, which is 4.  Therefore, this element has 2 valence electrons (4s2).  Due to this, the element is in group 2 on the periodic table. Elements on the left side of the periodic table are metals and are very reactive.

4.	What is the correct formula for potassium chlorate?  (3.02)
a.	PClO3				c.	KClO3	
b.	PCl				d.	K(ClO3)2

This is an ionic bond since potassium is a metal and it is bonding to chlorate (the -ate tells us this is a polyatomic ion).  Let’s write their charges.  Potassium is a main group metal, so its charge is given in that special periodic table.  For chlorate, we look at the list of polyatomic ions.
	K+		ClO3-	

It looks like we have +1 and -1, which equals 0.  So, we only need one of each ion: KClO3 

5.	What is the correct formula when aluminum bonds with hydroxide? (3.02)
a.	AlOH33			c.  OH3Al
b.	Al(OH)3			d.  Al(OH)2
Looking at a special periodic table of common charges as well as the polyatomic ion list,  we see that aluminum has a common charge of +3.  Hydroxide is a polyatomic ion with a common charge of -1.  We need to have an overall neutral charge.  How many of each ion do we need?  Look at it like an addition problem:
Al+3        OH-
    	   OH-
   OH-
---------------------
+3          -3       =  0     

Therefore, we get AlOH3...but WAIT!!!!  We need 3 hydroxide GROUPS, not one oxygen and 3 hydrogens.  In order to write this correctly, the polyatomic ion must be in parenthesis.  For ionic compounds, we always write the most electronegative ion first (99.99% of the time - that’s the metal!)  Al(OH)3

6.	What is the correct name for Pb3(PO4)2? (3.02)
a.	Lead phosphide		c.	Lead phosphate	
b.	Lead (II) phosphate		d.	Lead (III) phosphate

Since this is a metal and a polyatomic ion, it is an ionic bond.  Pb, lead, is a “special” metal that requires a Roman Numeral in its name (we like to refer to the transition metals, lead and tin as “special” in terms of naming rules).  Let’s figure out the charge of Pb as there is not one common charge for it.   The formula is  Pb3(PO4)2 So we know it takes 3 lead’s (unknown charge) and 2 phosphate groups (each has -3 charge) to be neutral.  Let’s write what we know:

Pb+?        PO4-3
Pb+?        PO4-3
Pb+?        
---------------------
+?             -6          

We need the total charge of Pb to equal +6 in order to balance the total charge from the phosphates (+6 - 6 = 0)

We have 3 Pb’s, therefore each Pb has a charge of +2. (3 times +2 = +6) 

Pb+2        PO4-3
Pb+2        PO4-3
Pb+2        
---------------------
+6             -6  = 0

Recall the Roman Numeral is the CHARGE of the special metal. Therefore, the Roman Numeral will be (II) in its name.  Lead (II) phosphate  

7.	Which of the following is a correct pair of formula and name? (3.02)
a.	CO:  monocarbon monoxide		c. SO2:  sulfur oxide
b.	N2O: dinitrogen oxide			d. BF3: boron trifluoride
All of these are covalent compounds since they are all nonmetals bonding to nonmetals.  We need to use the prefixes for naming covalent compounds.    We know that if there is only one of the first element, we just name it. No prefix needed. If there is more than one, then we use the corresponding prefix.  For the second element, we always use the prefix and change the ending to -ide.
CO - correct name is carbon monoxide
N2O: correct name is dinitrogen monoxide
SO2:  correct name is sulfur dioxide
BF3:  this is the correct name: boron trifluoride

8.	What is the charge of an atom that loses three electrons? (3.03)
a.	0	 			c.  +3 
b.	Not possible			d. - 3

We start with equal protons (positive) and electrons (negative).  If we lose 3 electrons, we will be positive overall.  For example, let’s look at an element with 10 protons and 10 electrons.  If we lose 3 electrons, then we have 7 electrons left:
10 protons = 10 electrons = 0 overall charge; neutral

10 protons = +10
7 electrons = -7 
Add them like in math class:   +10 - 7 = +3  (Since we have 3 extra protons, this makes sense)

9.	Which of the following best describes what happens when an ionic bond forms? (3.03)
a.	A metal accepts electrons from a nonmetal
b.	A nonmetal accepts electrons from a metal
c.	A metal donates electrons to a metal
d.	A nonmetal donates electrons to a nonmetal
Recall that metals will transfer their electrons to nonmetals to form an ionic bond. Metals are givers and nonmetals are takers! Note: there are a very small number of exceptions to this.

10.	What happens when the compound CaCl2 forms? (3.03)
a.	Calcium donates one electron
b.	Chlorine accepts two electrons
c.	Calcium accepts one electron
d.	Calcium donates two electrons
Looking at our special periodic table, we see that calcium has a common charge of +2.  Chlorine has a common charge of -1.  Therefore it will take two chlorines to balance calcium’s charge.
Ca+2        Cl-
               Cl-
---------------------
 +2         -2        = 0     

Therefore, we get:   CaCl2

The subscript in an ionic compound tells us how many of each ion is needed to have an overall neutral compound

11.	When one atom of lithium (Li) combines with one atom of chlorine (Cl), their bonding results in a molecule of LiCl. Which of the following describes the arrangement of valence electrons in a bond between Li and Cl? (3.03)
a.	The valence electrons spend more time around Li
b.	The valence electrons are given up by the Li and gained by the Cl	
c.	The valence electrons are shared equally between Li and Cl
d.	These two atoms will not form a bond.

Recall that metals will transfer their electrons to nonmetals to form an ionic bond. Metals are givers and nonmetals are takers! This is an absolute transfer, no sharing or spending more time around one.  Since this is a metal and a nonmetal, the ionic bond will form.

12.	Which of the following best describes the formula unit for a compound made from Li and S? (3.03)
a.	It is LiS because the total negative charge on S is one.
b.	It is Li2S because the total negative charge on S is two.
c.	It is Li2S because the total positive charge on Li is two.
d.	It is LiS because the total positive charge on S is one.

Lithium has a common charge of +1.  Sulfur has a common charge of -2.  We need to have an overall neutral charge.  How many of each ion do we need?  Look at it like an addition problem:
Li+        S-2
Li+     
---------------------
+2        -2       =  0     

Therefore, we get Li2S

The subscript in an ionic compound tells us how many of each ion is needed to have an overall neutral compound

13.	Which of the following best describes what is represented by the following Lewis Dot Structure? (3.03)

  
a.	Oxygen is accepting an electron to form a -1 charge
b.	Sodium  is donating two electrons to form a +2 charge
c.	Each sodium atom is donating one electron to oxygen, which will then have a  +2 charge
d.	Each sodium atom is donating one electron to oxygen, which will then have a -2 charge

14.	Which of the following pairs of elements could possibly be in the same group? (3.03)
a.	X has a +3 ion; Y has a -3 ion.
b.	X tends to form a +1 ion; Y has one valence electron.
c.	X will tend to gain two electrons; Y has two valence electrons.
d.	X has an atomic number 49; Y forms a +2 ion.

Look at the periodic table of common charges.  ‘A’ cannot be correct as giving and taking electrons does not happen in the same group.  C cannot be correct as if we had 2 valence electrons, we would lose them (look at group 2 metals!)  D cannot be correct as element 49 is indium, located in group 3A (or 13 - depending on the PT you are looking at).   That group forms +3 charge as they have 3 valence electrons.  B must be correct.  An element with one valence electron will lose it to form a +1 ion.

15.	Which of the following best compares ionic and covalent bonding? (3.04)
a.	Covalent bonding transfers electrons whereas ionic bonding shares electrons
b.	Ionic bonding transfers electrons whereas covalent bonding shares electrons
c.	Both ionic and covalent share electrons, but we draw their Lewis Dot Structures differently
d.	Both ionic and covalent transfer electrons, but we draw their Lewis Dot Structures differently

16.	Which of the following best describes the bonding in a molecule of H2S? (3.04)
a.	The sulfur atom shares an electron pair with each H atom.	
b.	Each hydrogen atom receives an electron pair from the sulfur atom.
c.	One hydrogen atom shares one electron with the other  H atom, which shares an electron with sulfur
d.	Each hydrogen atom shares an electron with the sulfur atom.

Since both elements are nonmetals, we know it will form a covalent bond.  Hydrogen has 1 valence electron and sulfur has 6 valence electrons (look at the valence electron periodic table).  Hydrogen wants to have 2 valence electrons to be stable (full outermost shell) and sulfur wants 8 valence electrons to be stable.  Therefore, each hydrogen will share its electron with sulfur.  Click HERE for the VSEPR making of H2S (ties in with 3.05)

17.	How many single bonds are in a molecule of nitrogen gas in its natural state? (3.04)
a.	0			c. 1
b.	2			d. 3

Nitrogen gas is diatomic in its natural state (see page 3). Recall there are 7 diatomic elements.  You will need this for module 4 (writing chemical reactions)   Nitrogen has 5 valence electrons.  Since there are only the two, they will need to share all three valence electrons with each other, creating a triple bond.  Therefore, there are 0 single bonds.

18.	As a covalent bond lengthens, what happens to its strength? (3.04)
a.	The strength increases. 				
b.	The strength decreases.
c.	The strength of a bond is not measurable.	
d.	There is no change to the strength of a bond.

See the diagram from page 3

19.	Select the best explanation for the formula that is formed when nitrogen bonds with hydrogen. (3.04)
a.	N3H because each hydrogen contributes three electrons to the triple bonds.
b.	NH3 because nitrogen contributes one electron to each of the single bonds.
c.	N3H because each hydrogen contributes three electrons to each of the single bonds.
d.	NH3 because each hydrogen contributes three electron pairs to the double bonds.

20.	Identify the molecular shape and number of domains for a molecule of silicon dioxide (SiO2). (3.05)
a.	Linear with two domains				
b.	Trigonal planar with two domains
c.	Linear with three domains			
d.	Trigonal planar with three domains
Note: Refer to lesson 3.05, page 4 for the basics of drawing Lewis Dot Diagrams for molecular (covalent) structures, which is needed to answer this question.  Silicon will most likely be the central atom since it is written first (is the case most of the time). Now, we must arrange the electrons to make “sense”.  Electrons repel each other, so the ones on the oxygens shift a little.  There are no lone electrons on Si, so the oxygens will be directly left and right.  Any nonbonding electrons on the central atom are what can cause the other atoms to shift creating other VSEPR shapes.

   →    

↓

21.	Which of the following is correct for a molecule of HCN? (3.05)

	VSEPR molecular shape	Total Domains (bonded/lone pairs) around central atom	
a	Trigonal Planar	1 total domain; 1 bonded pairs and two lone pairs 	
b	Bent	4 total domains; 3 bonded pairs and 0 lone pair	
c	Tetrahedral	4 total domains; 2 bonded pairs and two lone pairs	
d	Linear	2 total domains; 2 bonded pairs and no lone pairs	

   →    

									↓

CN is a polyatomic ion, so they must be bonded together.	

3.06 IMF’s summarized - PDF form will help you for questions 23 - 26

22.	Which of the following is NOT true about hydrogen bonding?  (3.06)
a.	It is an intermolecular force				
b.	It exists between any element and hydrogen.
c.	It is the 2nd strongest of all the intermolecular forces.	
d.	Water experiences hydrogen bonding.

23.	Electrostatic attraction of permanent dipoles in polar molecules is a definition of which type of intermolecular force?   (3.06)
a.	London Dispersion		c.  Dipole-dipole
b.	Ion-Dipole			d.  Hydrogen Bonding

24.	Which of the following is true of London Dispersion forces?   (3.06)
a.	The get weaker as the number of electrons increases
b.	They are a permanent attractive force between two adjacent molecules forming permanent dipoles.
c.	They occur between all particles and molecules.
d.	They are stronger than hydrogen bonding.

25.	Dipole-dipole interactions form between which types of molecules?  (3.06)
a.	Non-polar molecules		c.  Polar molecules
b.	Ionic compounds		d.  All of the above

26.	On the basis of strength of intermolecular forces, which of the following elements would be expected to have the highest melting point?  (3.06) All of the compounds will experience London Dispersion Forces. The compound with the  largest number of electrons should have the strongest dispersion force. Br2 has the greatest number of electrons, so the force is strongest and makes the melting point the highest.
a.	Br2 				c.  Cl2  
b.	F2  				d.  Kr
27.	For the previous question #27, why does that compound have the highest melting point?  (3.06)
a.	Because it has dipole-dipole forces while the others have london dispersion
b.	Because they all have london dispersion forces, but this compound has more electrons
c.	Because they all have dipole-dipole forces, but this compound has more electrons

28.	Which of the following substances has the highest boiling point?   Stronger intermolecular forces cause higher boiling points.  Ion-dipole is the strongest. None of these experience that force.  Hydrogen bonding is second strongest, of which there are two that experience hydrogen bonding.  The answer is H2O.  H2O has two places to form hydrogen bonds, NH3 only has one
a.	H2O			c.  Kr
b.	CO2			d.  NH3

29.	Which of the following molecules would be most polar? (3.06)
a.	H2			c.  HF
b.	HBr			d.  HCl
Right away, we can eliminate H2 as it is a diatomic molecule - about as nonpolar as you can get.  That leaves three compounds, all of which have hydrogen bonded to a nonmetal.  Looking at the IMF - HF will have hydrogen bonding, thus will be the more polar compound.

Essay format questions:
30.	The electron configuration of an element is: 1s2 2s2 2p6 3s2 3p6 4s2 (3.01)
a.	Identify the group name this element belongs to in the periodic table.Explain your answer.   This element has 2 valence electrons (4 is the highest energy level and it is full with 2 electrons).  The group on the periodic table with 2 valence electrons in 4s is the alkaline earth metals. 
b.	Based on the electron configuration, write one chemical and one physical property of this element.  Alkaline earth metals are very reactive, but less reactive than alkali metals. A physical property is that they are good conductors of electricity and heat.
31.	 What is the correct name for PdO2? Explain how you determined the charges of each element and how you named it.  (3.03)  Pd is the chemical symbol for Palladium, element #46 on the periodic table.  Since it is a transition metal, it will require a Roman numeral in its name.  We must work backwards, so to speak, to determine the charge of Pd. Let’s start with what we know:
Pd: it’s a metal, so it will be a positive charge.  Pd+?
O: this is oxygen, which we know has a -2 charge.  O-2
   
Looking at the formula, we have 1 Pd and 2 O’s:

Pd+?         O-2
                    O-2
__________
+?          -4    = 0

Since the positives have to equal the negatives, we now know that Pd must have a charge of +4.

Pd+4         O-2
                    O-2
__________
+4          -4    =   0

To answer the question, we must give the correct name.  PdO2 is palladium (IV) oxide.

Honors Extension (all MC on the exam):

32.	(3.07H) What does the picture to the right represent? 
a.	Amine 			c.  Alcohol
b.	Polymer		d.  Carbohydrate

If you had trouble with this, please be sure you have all the organic compound structures and names in your notes.  

Organic chemistry summary                 Organic functional groups help video
                       (will help for questions 34-35).

33.	(3.07H) Which group has an oxygen atom bonded between two carbon atoms in the carbon chain and are not very soluble in water.
a.	Amine			c. Ether
b.	Carbohydrate		d. Alcohol

34.	(3.07H) In an experiment, two unknown compounds (one an amine and the other an alcohol) of equal molecular mass were dissolved in water. The result of the experiment is shown in the table. 
Solubility Comparison
Unknown Compound	Solubility 
(g/100mL water)	
A	5.9	
B	4.6	

Which of the following correctly explains the identity of Compound A and its solubility?
a.	It is an alcohol because the lack of hydrogen bonding between the OH− groups make it less soluble.
b.	It is an amine; because the lower electronegativity of N than H makes it more soluble.
c.	It is an amine; it contains a nitrogen atom that will allow nitrogen-hydrogen bonds to form while in water and they are stronger than the oxygen-hydrogen bonds.
d.	It is an alcohol because the hydrogen bonding is more polar than the N - C bonds and makes it more soluble.

See page 4 of the lesson for more information.

35.	(3.07H) All of the following are properties of carbon, except: 
a.	Has 3 valence electrons		c. Can form double bonds
b.	Can form bonds with 4 atoms		d. Can form rings
Carbon is in group 4A, and has 4 valence electrons.  It can form 4 single bonds, or a combination of single, double, triple bonds - depending on the other element(s)