Chem 22 Test 2
1.
Name_________________________
Carbon combines with Hydrogen to make methane, an unbalanced equation describing that
reaction is
C(s) + H2(g)  CH4(g)
Balance this equation and then answer the following questions:
a. How many moles of Hydrogen gas are required to react completely with one mole of
Carbon? Carbon MW=12.01g/mol Hydrogen MW=1.008g/mol.
b. If 3 grams of carbon react with one gram of Hydrogen gas, how many grams of methane are
produced? How many molecules of methane are produced?
c. How much (if any) of the reactants (grams and moles) remain after the reaction goes to
completion?
2. The lewis structure of Carbon can be written as
indicating that carbon has four
electrons in its valence shell that are available for bonding with other atoms. The lewis
structure of Hydrogen is written as
indicating that Hydrogen has one electron in its
valence shell available for bonding with other atoms. Carbon atoms and Hydrogen atoms will
bond covalently with each other in a way that makes all bonded atoms feel like they have a full
valence shell. For Carbon atoms this necessitates that there are eight electrons (an octet) in its
valence shell and for Hydrogen atoms this necessitates that there are two electrons in its
valence shell (hydrogens valence shell consists only of the 1S sublevel). Starting with the Lewis
structures given for carbon atoms and hydrogen atoms, draw the lewis structure of methane.
Chem 22 Test 2
Name_________________________
3. The above lewis structure for methane should indicate that the methane molecule is composed
of a central carbon atom that is surrounded by four objects (the bound hydrogen atoms)
projecting from its center. When a central atom has objects projecting from its center (bonded
atoms or lone electron pairs) those objects will move to positions that maximize their separation
from each other.
a. Why do bonded atoms and lone electron pairs surrounding a central atom move to
positions that maximize their separation from each other? (circle one).
i. Bonds and lone pairs are made of negatively charged electrons which repel each
other and so these groups will move away from each others repulsive forces.
ii. Groups bound to a central atom have volumes that they occupy and so the
groups will move away from each other to allow room for their volumes.
iii. 42
iv. i. and ii. are correct.
b. What geometric arrangement will the objects (in this case only hydrogen atoms)
surrounding the central Carbon atom arrange themselves in?
i. Pyramidal
ii. Trigonal Planar
iii. V-shaped
iv. Tetrahedral
c. What is the shape of the Methane molecule?
i. Pyramidal
ii. Trigonal Planar
iii. V-shaped
iv. Tetrahedral
d. In the methane molecule we have an example of a central atom with four identical
bound atoms (which have identical pull on the central atoms (carbons) valence
electrons) surrounding the central atom from geometrically equivalent positions in
space. There are no lone electron pairs on the central atom. Does this arrangement
result in a molecule that is polar or non-polar? Explain.
Chem 22 Test 2
Name_________________________
e. The molecule Ammonia, NH3, is composed of a central nitrogen atom bound to three
hydrogen atoms. This molecule, like methane, has four different objects surrounding a
central atom, but its lewis structure indicates that only three of these objects are bound
atoms. Draw the Lewis structure of Ammonia and identify the other type of object that
surrounds the central Nitrogen atom.
f.
What then is the shape of the Ammonia molecule?
i. Pyramidal
ii. Trigonal Planar
iii. V-shaped
iv. Tetrahedral
g. Is the ammonia molecule a polar or a non-polar molecule?
4. Methane generated in the above reaction can be reacted with Chlorine gas to form chloroform
(CH3Cl) according to the following unbalanced equation:
CH4 + Cl2 CHCl3 + HCl
Balance the equation and then answer the questions.
a. If nine moles of Cl2 are reacted with four moles of CH4, how many moles of CH3Cl are
produced?
b. How many molecules of CH3Cl is this?
c. From part a, how many moles (if any) of the reactants remain after the reaction goes to
completion?
Chem 22 Test 2
Name_________________________
The Chloroform molecule generated in the above reaction, like methane, is a molecule that
consists of a central atom that has four bonded atoms (and no lone pairs) surrounding it from
equivalent positions in space, but now those bonded atoms do not have identical pull on the
central atoms valence electrons. In fact, the chlorine atoms pull on carbons valence electrons
much more strongly than does the hydrogen atom (your book assigns Chlorine a relative electro
negativity of 3.0 while it only assigns Hydrogen a relative electro negativity of 2.1.
d. Describe the general distribution of electrons around the chloroform molecule. Does
one side of the molecule have more negative charge than the other side? If so, which
side of the molecule is this and which side has more positive charge?
e. Is the chloroform molecule then a polar or a non-polar molecule?
f.
Is the byproduct of the reaction, HCl, a polar or a non-polar molecule? Explain using the
relative electro negativities of H and Cl given in the problem.
5. Suppose that instead of reacting Methane with Chlorine, we instead react it with Oxygen to
produce formaldehyde and water. The equation for this reaction and the lewis structure are
given.
CH4 + O2  CH2O + H2O
a. Formaldehyde also has a central Carbon atom with bonded groups surrounding it. How
many total groups (bonded atoms and lone electron pairs (if any) are projecting from
the central atom in this molecule?
Chem 22 Test 2
Name_________________________
b. What is the resultant shape of the Formaldehyde molecule? Circle one.
i. Trigonal Pyramidal
ii. Trigonal Planar
iii. Tetrahedral
iv. V-shaped
c. Is Formaldehyde a polar or a non-polar molecule? Explain using the relative electro
negativities of the bound atoms Hydrogen (2.1) and Oxygen (3.5).
The activity series presented here lists metals and halogens in order of increasing “activity”. In
this table “activity” is defined differently for metals and halogens. For the metals a high activity
indicates that a metal has relatively weaker attraction for its valence electrons than does a
metal with lower activity, and so it will tend to lose electrons to form positively charged ions
more readily and also will lose electrons to an ion of a metal with a lower activity. Notice that
the metals with the lowest activities are the metals we use to make jewelry since they don’t
tend to decompose into their positively charged ions as readily. For the halogens the definition
of activity is the opposite. A halogen with a high activity has a stronger pull for electrons than
does a halogen with a lower activity, and so a halogen with a higher activity tends to gain
electrons more readily forming negatively charged ions (halide) and will tend to take electrons
from a halide with a lower activity.
Chem 22 Test 2
Name_________________________
6. Imagine now the interaction between a metal in its solid state (it still possesses all of its valence
electrons) and a solution of HCl. In the acid solution the very electronegative chlorine atom has
effectively stolen the valence electron formerly belonging to Hydrogen. In solution this leaves
hydrogen as the positively charged H+ ion. This ion would like to gain electrons, but in order to
do so it must find a metal weaker than it (higher activity) so that it can steal electrons from that
atom. If the Hydrogen in solution has a stronger pull on electrons than the metal, the reaction
proceeds to form hydrogen gas and a metal-halide. The following equation is an example of this
reaction:
HCl (aq) + Mg(s)  H2(g) + MgCl2(aq)
a. Balance this equation
b. How many moles of HCl are required to react with four moles of Mg(s)?
c. Which atoms have lost electrons, which atoms have gained electrons and which atoms have
not lost or gained electrons in this reaction?
d. Draw the lewis structure of H+ and H. Use the lewis structure of H to show how two H
atoms bond together to form the molecule H2 which provides a filled valence (1S sublevel)
for each Hydrogen. Is H2 a polar or non-polar molecule?
e. For the following scenarios determine whether or not the reactants combined will go on to
form products. If any of the reactions do lead to product formation, write the balanced
chemical equation that describes the reaction.
a. HCl(aq) + Fe(s)  ?
b. HCl(aq) + Ag(s)  ?
Chem 22 Test 2
Name_________________________
7. Imagine now a scenario in which a metal-halide solution has a halogen gas bubbled through it.
In this scenario we have set up a competition between two electron hungry halogens for the
electrons formerly held by the metal atom. The halide present in the metal-halide solution
already possesses these electrons and exists as the negatively charged anion. The halogen in
the gas has not yet found a suitable electron source and so has formed covalent bonds with
other atoms of its type to attain octet stability. If the halogen in the gas has a stronger pull for
electrons than the reduced halide in the metal-halide solution, it will take those electrons away
from the weaker halogen and replace it as the negative ion in the metal-halide solution. Upon
losing its electron, the formerly negatively charged halogen will be forced to bond covalently
with another atom of its type forming its diatomic gas.
a. Draw the lewis structures of the Bromine atom and the bromine ion. Verify that the
bromine ion has octet stability (eight electrons in its valence shell) and that the bromine
atom does not.
b. Use Lewis structures to show how two Bromine atoms form a covalent bond making a
diatomic molecule in which both atoms “feel” like they have eight electrons in their
valence shell.
c. Is the diatomic Bromine molecule (Br2) a polar or a non-polar molecule?
d. Based on the above logic, determine which of the following scenarios will lead to a
reaction. If any do, write and balance the equation that describes the reaction.
i. HBr(aq) + Cl2(g)  ?
ii. HBr(aq) + I2(g)  ?
Chem 22 Test 2
Name_________________________
8. The activity series for the halogens (F, Cl, Br, I) seems to suggest that that halogens towards the
top of the periodic table, which have smaller atomic radii, have a stronger pull for electrons than
do the halogens towards the bottom of the periodic table which have larger atomic radii. Why
is it that atoms within this family, atoms that have identical valence configurations, demonstrate
size-based differences in their overall electro negativities? Explain using the concept that
energy is released when a negative charge approaches a positive charge.
9. Does atomic size increase or decrease moving down a column (staying in the same family) in the
periodic table? Explain.
10. Does atomic size increase or decrease moving across a row (staying in the same principle energy
level) in the periodic table? Explain.
Chem 22 Test 2
Name_________________________
11. Which is larger, the Chlorine atom or the chlorine ion? Explain.
12. Which is larger, the Magnesium atom or the Magnesium ion? Explain.
13. Write the electron configurations and the orbital diagrams of the magnesium atom and the
magnesium ion. These are the diagrams that indicate the placement of electrons in their
orbitals. Do not use the abbreviated electron configuration.
14. How many electrons can fit into a single electron orbital?
a. 1
b. 2
c. 6
d. 10
15. Consider the fourth principle energy level…
a. How many S-orbital’s are in this level and, in total, how many electrons can be placed in
them/it?
b. How many P-orbital’s are in this level and, in total, how many electrons can be placed in
them?
c. How many D-orbital’s are in this level and, in total, how many electrons can be placed in
them?
Chem 22 Test 2
Name_________________________
16. When placing electrons within a principle energy level that has multiple orbital’s available, the
electrons will be placed in the lowest energy orbital’s first and once those orbital’s are filled,
electrons will be placed in the next higher energy orbital and so on. Assume a given principle
energy level has D, P and S orbital’s available, place these orbital types in the order in which
they will be filled. In other words list them in order of increasing energy. Circle one.
a. D  P  S
b. P  D  S
c. S  P  D
d. S  B  D