CEM 141
CEM 141 MSU Exam 2 Study
Questions and Answers Graded A+
Which reaction requires the most energy?
A. N(g) → N+(g) + e -
B. N+(g) → N2+(g) + e -
C. F(g) → F+(g) + e -
D. F+(g) → F2+(g) + e - -Correct Answer ✔-D. F+(g) → F2+(g) + e -
Fluorine has a higher effective nuclear charge than Nitrogen - so it is harder to
remove an electron (takes more energy because the electron is more strongly
attracted by the nucleus). Effective nuclear charge is the same for F and F+
because the number of protons and core electrons are not changed. However,
when the number of electrons is reduced, the repulsion between electrons
decreases which results in a decrease in the radius of the electron cloud because
the point at which attractions and repulsions are balanced is closer to the nucleus
when there is less repulsion. When the radius of the electron cloud decreases, the
strength of the attraction between the nucleus and the valence electrons
increases which increases the amount of energy required to remove an electron
(ionization energy).
Which has a larger atomic radius? Mg or Ar and why. -Correct Answer ✔-Mg,
because its valence electrons are not as strongly attracted towards the nucleus as
those in Ar.
The effective nuclear charge on Mg is smaller - on Ar the electrons are more
strongly attracted and therefore the electron cloud shrinks in towards the nucleus
until the e-e repulsions come into effect.
Consider the isoelectronic (they all have the same number of electrons) species
Na+, Mg2+, Ne, and F-, which of these has the smallest radius? -Correct Answer
✔-Mg2+
CEM 141
, CEM 141
All the species have the same number of electrons - but different number of
protons. Mg2+ has the highest proton to electron ratio and therefore the highest
effective nuclear charge and the strongest attraction between the protons and
electrons - which pulls the electron cloud towards the nucleus until the repulsions
take effect.
When and where were the carbon and oxygen atoms in your body created? -
Correct Answer ✔-Within stars and stellar explosions
Iodine exists as molecules of I2 and silicon dioxide exists as an extended network
of Silicon-oxygen bonds (similar to diamond). They both are solids at room
temperature, but which do you think has the higher melting point and why? -
Correct Answer ✔-Silicon dioxide because to melt it you would have to break
covalent bonds.
Does one molecule of water have a boiling point? -Correct Answer ✔-No
Why does one molecule of water not have a boiling point? -Correct Answer ✔-The
boiling point is the temperature at which the particles change from liquid to gas. If
there is only one particle the words liquid and gas (and solid for that matter) are
meaningless.
Why do covalent bonds form? -Correct Answer ✔-- Because electrons from one
atom are attracted to the nucleus of another atom.
- Because the formation of a bond results in a stable system that would require
the input of energy to change.
Which of the following are correct statements?
I. Covalent bonds are interactions within molecules.
II. Covalent bonds are interactions between separate molecules.
III. LDFs are typically interactions between separate molecules, but can occur
within a single large molecule.
CEM 141
CEM 141 MSU Exam 2 Study
Questions and Answers Graded A+
Which reaction requires the most energy?
A. N(g) → N+(g) + e -
B. N+(g) → N2+(g) + e -
C. F(g) → F+(g) + e -
D. F+(g) → F2+(g) + e - -Correct Answer ✔-D. F+(g) → F2+(g) + e -
Fluorine has a higher effective nuclear charge than Nitrogen - so it is harder to
remove an electron (takes more energy because the electron is more strongly
attracted by the nucleus). Effective nuclear charge is the same for F and F+
because the number of protons and core electrons are not changed. However,
when the number of electrons is reduced, the repulsion between electrons
decreases which results in a decrease in the radius of the electron cloud because
the point at which attractions and repulsions are balanced is closer to the nucleus
when there is less repulsion. When the radius of the electron cloud decreases, the
strength of the attraction between the nucleus and the valence electrons
increases which increases the amount of energy required to remove an electron
(ionization energy).
Which has a larger atomic radius? Mg or Ar and why. -Correct Answer ✔-Mg,
because its valence electrons are not as strongly attracted towards the nucleus as
those in Ar.
The effective nuclear charge on Mg is smaller - on Ar the electrons are more
strongly attracted and therefore the electron cloud shrinks in towards the nucleus
until the e-e repulsions come into effect.
Consider the isoelectronic (they all have the same number of electrons) species
Na+, Mg2+, Ne, and F-, which of these has the smallest radius? -Correct Answer
✔-Mg2+
CEM 141
, CEM 141
All the species have the same number of electrons - but different number of
protons. Mg2+ has the highest proton to electron ratio and therefore the highest
effective nuclear charge and the strongest attraction between the protons and
electrons - which pulls the electron cloud towards the nucleus until the repulsions
take effect.
When and where were the carbon and oxygen atoms in your body created? -
Correct Answer ✔-Within stars and stellar explosions
Iodine exists as molecules of I2 and silicon dioxide exists as an extended network
of Silicon-oxygen bonds (similar to diamond). They both are solids at room
temperature, but which do you think has the higher melting point and why? -
Correct Answer ✔-Silicon dioxide because to melt it you would have to break
covalent bonds.
Does one molecule of water have a boiling point? -Correct Answer ✔-No
Why does one molecule of water not have a boiling point? -Correct Answer ✔-The
boiling point is the temperature at which the particles change from liquid to gas. If
there is only one particle the words liquid and gas (and solid for that matter) are
meaningless.
Why do covalent bonds form? -Correct Answer ✔-- Because electrons from one
atom are attracted to the nucleus of another atom.
- Because the formation of a bond results in a stable system that would require
the input of energy to change.
Which of the following are correct statements?
I. Covalent bonds are interactions within molecules.
II. Covalent bonds are interactions between separate molecules.
III. LDFs are typically interactions between separate molecules, but can occur
within a single large molecule.
CEM 141
