1.) Which is the correct electron dot representation of an atom of chlorine in the ground state?
(A)
Cl :
(B)
(C)
(D)
.
..
..
: Cl .
: Cl :
: Cl :
.
.
..
ANSWER = C b/c chlorine is in Group 17 of the periodic table – and elements in Group 17 have 7
valence electrons. So, Cl should have 7 dots around it
2.) What is the probable formula for sodium sulfide? (Sulfur has atomic number 16.)
(A)
NaS
(B)
Na2S
(C)
Na3S
(D)
NaS2
ANSWER = B b/c Na is in Group 1 and has an oxidation # of +1 and sulfur is in Group 16 and has an
oxidation number of -2.
Na+1 S-2
Na+1 S-2
Na2S
3.) Which element could X represent in this electron dot structure?
:X:::X:
(A)
chlorine
(B)
hydrogen
(C)
nitrogen
(D)
oxygen
ANSWER = C b/c there is a total of 10 dots in the Lewis structure. Total of 10 dots means that each X
has 5 valence electrons. Group 15 elements have 5 valence electrons. Nitrogen is in Group 15.
4.) To determine the density of an irregularly-shaped object, a student immersed the object in 30.0
milliliters of H2O in a graduated cylinder, causing the level of the H2O to rise to 36.1 milliliters. If the
object had a mass of 25.3 grams, what is the density of the object?
(A)
4.1 g/mL
(B)
0.84 g/mL
(C)
2.6 g/mL
(D)
0.24 g/mL
ANSWER = A b/c density = mass divided by volume. Mass is 25.3 grams (The unit “grams” tells you
that it is mass.). Volume is 36.1 mL – 30.0 mL = 6.1 mL. Density equals 25.3 g / 6.1 mL = 4.1 g/mL
5.) Which set of coefficients correctly balances the equation?
__ Al2O3 --> __ Al + __ O2
(A)
1, 2, 1
(B)
2, 2, 3
(C)
2, 3, 4
(D)
2, 4, 3
ANSWER = D b/c a balanced equation contains the same number of atoms of each element on both
sides of the arrow. By putting a “2” in front of Al2O3 there are 4 Al atoms and 6 O atoms (multiply
subscript by coefficient). In order to have 4 Al atoms on the right hand side of the arrow, there needs
to be a “4” in front of the Al. In order to have 6 O atoms on the right hand side of the arrow, there
needs to be a “3” in front of the O2 (multiply subscript by coefficient).
6.) Which molecule contains a polar covalent bond?
(A)
:N:::N:
(B)
H:H
(C)
:O::O:
..
..
(D)
..
:O:H
..
H
ANSWER = D b/c a polar covalent bond occurs between two DIFFERENT nonmetals
7.) When the following equation is completely balanced using smallest whole numbers, what would be
the coefficient of O2?
C2H4 + __ O2 --> CO2 + H2O
(A)
2
(B)
3
(C)
4
(D)
6
ANSWER = B (See answer to #5.) In order to “balance” the carbons, there needs to be a “2” in front
of the CO2 on the right hand side. In order to “balance” the hydrogens, there needs to be a “2” in
front of the H2O on the right hand side. This means that there is a total of 6 oxygens on the right
hand side – 4 from the “2 CO2” and 2 from the “2 H2O”. To get 6 oxygens on the left hand side, there
needs to be a “3” in front of the O2.
8.) The mass of a solid is 7.20 grams and its volume is 3.6 cubic centimeters. What is the density of
the solid, expressed to the correct number of significant figures?
(A)
2.0 g/cm3
(B)
2.00 g/cm3
(C)
0.50 g/cm3
(D)
0.500 g/cm3
ANSWER = A (See answer to #4.) Mass is 7.20 grams – which has 3 significant figures. Volume is
3.6 cubic centimeters (cm3) – which has 2 significant figures. 7.20 divided by 3.6 equals 2. The
answer to the problem must have the same number of significant figures as the number in the problem
with the FEWEST significant figures.
9.) An unknown element is brittle and is found to be a poor conductor of electricity. What other
property would you predict the element to have?
(A)
shiny
(B)
ductile
(C)
dull
(D)
malleable
ANSWER = C b/c if an element is brittle and a poor conductor of electricity, it is probably a NONmetal.
Another property of nonmetals is that they are dull (not shiny).
10.) This is an example of what kind of reaction?
4 Al (s) + 3 O2 (g) --> 2 Al2O3 (s)
(A)
synthesis
(B)
decomposition
(C)
combination
(D)
ionic
ANSWER = A Use p. iii in the yellow booklet for help. Synthesis reactions have only one substance on
the right hand side of the arrow.
11.) An atom that has an electron configuration of 1s2 2s2 2p6 3s2 3p6 4s1 is classified as which of the
following?
(A)
an alkali metal
(C)
a noble gas
(B)
an alkaline earth metal
(D)
a transition element
ANSWER = A b/c the electron configuration ends with 4s1 and that means that it is in Group 1 – which
is the alkali metals. OR, if you add up all of the exponents in the electron configuration, you get 19.
The element with atomic # 19 is potassium (K) – which is in Group 1.
12.) In which compound are electrons shared with the oxygen atom?
(A)
Na2O
(B)
CO2
(C)
Al2O3
(D)
CuO
ANSWER = B b/c when electrons are shared between two elements, it is a covalent bon(D) Covalent
bonds occur between two or more nonmetals.
13.) In an atom that has an electron configuration of 1s2 2s2 2p5 , what is the total number of electrons
in its sublevel of highest energy?
(A)
2
(B)
5
(C)
7
(D)
9
ANSWER = B b/c 2 is the highest occupied energy level (HOEL) – b/c 2 is the largest non-exponent
(coefficient) #. If you add up the exponents of the terms that have a “2” in front of them, you get 5.
OR, if you add up all of the exponents, you get 7. The element with atomic number 7 is nitrogen (N).
It is in Group 15, so it has 5 valence electrons.
14.) What is the correct name for the compound with the formula FeSO4?
(A)
iron (II) sulfate
(C)
iron (II) sulfide
(B)
iron (I) sulfate
(D)
iron (I) sulfide
ANSWER = A b/c the formula has more than 2 elements, it is a tertiary compoun(D) The 1st element
is a metal that is not in Group 1 or Group 2 or Al, Zn, or Ag, so there needs to be a Roman numeral.
(DUH! All the answer choices have Roman numerals!  ) The metal (Fe) is iron. (Again with the
“DUH!”) The 2nd part of the formula is SO4 – and that is “sulfate” polyatomic ion. That eliminates
answer choices c and (D) To determine the Roman numeral, sulfate (SO4) has a -2 oxidation #. In
order to “cancel out” the 2 negatives, there needs to be 2 positives, so the Roman numeral is 2.
15.) As the elements of group 2 are considered in succession from top to bottom, there is a general
increase in
(A)
electronegativity
(C)
ionization energy
(B)
metallic character (D)
nonmetallic character
ANSWER = B b/c the most metallic elements are at the bottom left of the Periodic Table.
(Electronegativity is highest at the top of Group 17 (fluorine). Ionization energy is highest at the top
right of the Periodic Table (helium). Nonmetallic character is highest at the top of Group 17 (fluorine).)
16.) An atom of an element contains 17 protons, 18 neutrons, and 17 electrons. What is this element?
(A)
an alkaline earth metal
(C)
a halogen
(B)
an alkali metal
(D)
a noble gas
ANSWER = C b/c the element w/ 17 protons MUST be chlorine (Cl) – Chlorine is in Group 17, and
Group 17 is called the halogens.
17.) The percent by mass of sulfur in H2SO4 (formula mass = 98) is closest to which of the following?
(A)
2.0 %
(B)
16 %
(C)
33 %
(D)
65 %
ANSWER = C Find “molar mass” of H2SO4.
H: 2 x 1.0079 = 2.0158
S: 1 x 32.066 = 32.066
TOTAL = 98.0794 (unit is grams per mole if you’re interested)
% sulfur = 32.066 x 100 = 32.6934 % or approximately 33 %
98.0794
O: 4 x 15.9994 = 63.9976
18.) Consider the unbalanced expression:
__ C6H12O6 (s) + __ O2 (g) --> __ CO2 (g) + __ H2O (g)
Which set of coefficients balances the equation?
(A)
1, 9, 6, 6
(B)
2, 9, 12, 12 (C)
1, 6, 6, 6
(D)
1, 6, 6, 12
ANSWER = C (See answers to #5 and #7.) The “(s)” and “(g)” do not affect how the equation is
balanced.
19.) What is the total number of sodium atoms in 46.0 grams of sodium?
(A)
3.01 x 1023
(B)
6.02 x 1023
(C)
1.20 x 1024 (D)
2.40 x 1024
ANSWER = C b/c there are 6.022 x 1023 atoms in 1 mole. 1 mole of an element is = to the molar
mass of the element. The molar mass of sodium is approximately 23 grams per mole. So, 46.0 grams
divided by 23 grams per mole = 2 moles. 2 moles x 6.022 x 1023 is approximately equal to 1.20 x 1024
atoms.
20.) Two atoms with an electronegativity difference of 1.2 form a bond that is
(A)
covalent, because electrons are shared
(B)
ionic, because electrons are shared
(C)
ionic, because electrons are transferred
(D)
covalent, because electrons are transferred
ANSWER = A b/c a bond is covalent if the difference in electronegativity between the two elements is
less than 1.7. By definition, a covalent bond involves the sharing of electrons.
21.) Which represents a polar molecule?
(A)
Cl2
(B)
N2
(C)
CCl4
(D)
NH3
ANSWER = D You know answers A and B are not polar because they are only two atoms of the same
element, which means that the bond between them is nonpolar covalent. If the bond is nonpolar
covalent, then the molecule is nonpolar. Answer C is not correct b/c there are no unshared electron
pairs on the central atom and all of the surrounding atoms are chlorine. Answer D is correct b/c there
is an unshared pair of electrons on the central atom (nitrogen).
22.) What is the correct formula for potassium oxide?
(A)
PO2
(B)
P2O
(C)
KO2
(D)
ANSWER = D
K2O
K+1 O-2
K+1 O-2
23.) Which of the following elements has the highest electronegativity?
(A)
N
(B)
O
(C)
F
(D)
K2O
Ne
ANSWER = C b/c electronegativity is highest at the top of Group 17 (fluorine). Electronegativity is
how much an atom wants to gain an electron. Group 17 has 7 valence electrons and only need to gain
1 electron to get 8.
24.) Which is the correct formula for lead (II) phosphate?
(A)
PbPO4
(B)
Pb4PO4
(C)
Pb3(PO4)2
(D)
Pb2(PO4)3
ANSWER = C
Pb+2 PO4-3
Pb+2 PO4-3
Pb3(PO4)2
(Pb’s oxidation # is +2 b/c the Roman numeral tells the oxidation # of the first element.)
25.) The bonding in NaCl is most similar to the bonding in which of the following?
(A)
BF3
(B)
CO2
(C)
MgO
(D)
H2O
ANSWER = C b/c NaCl has a metal and a nonmetal in the formula – which means it has ionic bonding.
MgO also has a metal and a nonmetal in the formula.
26.) Which formula correctly represents iron (II) sulfide?
(A)
FeS
(B)
FeSO3
(C)
Fe2S3
(D)
ANSWER = A
Fe+2 1 S-2 1
Fe+2 S-2
Fe+2 S-2
Fe2(SO4)3
FeS
27.) The atomic number of an atom is always equal to the
(A)
number of protons
(C)
number of protons and neutrons
(B)
number of neutrons
(D)
mass number
ANSWER = A b/c the definition of atomic # is the number of protons
28.) A S-2 ion differs from an S atom in that the S-2 ion has
(A)
more electrons
(B)
more protons
(C)
fewer electrons
(D)
fewer protons
ANSWER = A b/c a -2 oxidation # means that the atom has gained 2 electrons
29.) Elements in the same group on the Periodic Table have the same
(A)
electronegativity
(C)
atomic radius
(B)
ionization energy
(D)
number of valence electrons
ANSWER = D b/c they do. I sure hope you know this by now. 
30.) When a chlorine atom becomes a chloride ion, what happens to the size of the atom?
(A)
increases by gaining an electron
(C)
decreases by gaining an electron
(B)
increases by losing an electron
(D)
decreases by losing an electron
ANSWER = A b/c chlorine (Cl) has 7 valence electrons (it’s in Group 17). It wants to gain 1 electron
to have 8. When an atom gains electrons, it gets bigger.
31.) Which three elements have the most similar chemical properties?
(A)
N, O, F
(B)
Hg, Br, Rn
(C)
Li, Na, K
(D)
Al, Si, P
ANSWER = C b/c elements in the same group have similar properties (PERIODIC LAW!!!  )
32.) Which formula represents a trigonal pyramidal molecule?
(A)
Br2
(B)
NH3
(C)
H2O
(D)
CH4
ANSWER = B b/c trigonal pyramid shaped molecules are in the class AB3E. That means that there
must be one central atom and 3 surrounding atoms. NH3 is the only answer choice with 3 surrounding
atoms.
33.) What is the empirical formula of the compound whose molecular formula is P4O10?
(A)
PO
(B)
PO2
(C)
P2O5
(D)
P8O20
ANSWER = C b/c an “empirical formula” is the most reduced formula. Look at the subscripts in the
formula. If ALL of the subscripts can be reduced (they are all divisible by the same #), then simplify
them to get the empirical formula. If all of the subscripts are not divisible by the same #, then what is
written is the empirical formula.
34.) The alkali metal having the smallest atomic radius is found in which period?
(A)
1
(B)
2
(C)
6
(D)
7
ANSWER = A b/c the LARGEST atomic radius is at the bottom of Group 1, so the smallest atoms are at
the top of the group. (The reason is b/c there are more occupied energy levels as you move down the
group.)
35.) What is the usual atomic ratio in which Group 13 elements react with those from Group 17?
(A)
3:7
(B)
7:3
(C)
1:3
(D)
3:1
ANSWER = C Let’s say element X is in Group 13. So it has an oxidation # of +3. Let’s say element Y
is in Group 17, so it has an oxidation # of -1.
X+3 Y-1
X+3 Y-1
XY3
So, the atomic ratio is 1 atom of X for every 3 atoms of Y.
36.) What is the probable formula for the oxide of element X in Group 1 of the periodic table?
(A)
XO
(B)
XO2
(C)
X2O
(D)
X2O2
ANSWER = C Element X has an oxidation # of +1. Oxygen has an oxidation # of -2.
X+1 O-2
X+1 O-2
X2O
37.) A molecule of carbon dioxide (CO2) contains which of the following?
(A)
ionic bonds only
(C)
covalent bonds only
(B)
both ionic and covalent bonds
(D)
neither ionic nor covalent bonds
ANSWER = C b/c covalent bonds occur between nonmetals
38.) How many electrons can the fourth energy level hold?
(A)
16
(B)
8
(C)
32
(D)
18
ANSWER = C b/c you remember that the formula to figure out the maximum # of electrons in an
energy level = 2 n2 (where n = # of the energy level), so 2 . (4)2
2 . 16 = 32
OR, 4th energy level has 4 sublevels (s, p, d, and f). “s” can hold 2 electrons. “p” can hold 6 electrons.
“d” can hold 10 electrons. “f” can hold 14 electrons. 2 + 6 + 10 + 14 = 32
39.) Using VSEPR theory, what shape does ammonia (NH3) resemble?
(A)
linear
(C)
tetrahedral
(B)
trigonal pyramid
(D)
trigonal planar
ANSWER = B b/c trigonal pyramid has an unshared electron pair on the central atom
N: 1 x 5 e- = 5
..
H: 3 x 1 e- = 3
H : N : H
8 dots
..
H
40.) When electrons are unequally shared, a bond is said to be which of the following?
(A)
nonpolar covalent
(C)
ionic
(B)
polar covalent
(D)
metallic
ANSWER = B b/c the definition of a polar covalent bond is that electrons are shared UNequally. (It
occurs between 2 different nonmetals.)
41.) What is the name of the compound whose formula is P2O4?
(A)
phosphorus tetroxide
(C)
diphosphorus tetroxide
(B)
diphosphorus oxide
(D)
phosphorus oxide
ANSWER = C b/c “di-“ is the prefix for 2 and “tetra-“ is the prefix for 4
42.) A compound has the molecular formula C2H4. What could be its empirical formula?
(A)
CH2
(B)
C2H
(C)
C4H2
(D)
C4H4
ANSWER = A (See answer to #33.)
43.) What mass contains 3.0 x 1023 atoms?
(A)
6.0 g of carbon
(C)
(B)
35 g of bromine
(D)
23 g of sodium
3.0 g of iodine
ANSWER = A b/c there are 6.022 x 1023 atoms in 1 mole. And 1 mole is equal to the molar mass of
an element. 3.0 x 1023 atoms is approx. = to 0.5 moles (or ½ of a mole). So, the answer should be
0.5 times the molar mass (or half of the molar mass) of the element.
44.) Calcium forms an ion with a charge of
(A)
2+ by gaining two electrons
(B)
2+ by losing two electrons
(C)
(D)
2- by gaining two electrons
2- by losing two electrons
ANSWER = B b/c Ca is in Group 2, so it has 2 valence e-. It would rather lose 2 e- than try to gain 6
e-. When an atom loses electrons, it becomes a POSITIVE ion.
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