MCAT General Chemistry Questions exam
review
Which of the following increases with increasing atomic number within a family
on the periodic table?
A) electronegativity
B) electron affinity
C) atomic radius
D) ionization energy - C) atomic radius
Only atomic radius increases going down a column. Size of an atom is determined
not only by effective nuclear charge, but also by number of electron shells.
Moving down a column, the number of electron shells increases. Because the
additional shells require additional space, atomic radius increases as number of
electron shells increases.
Which of the following most likely represents the correct order of ion size from
greatest to smallest?
A) O2-, F-, Na+, Mg2+
B) Mg2+, Na+, F-, O2-
C) Na+, Mg2+, O2-, F-
D) Mg2+, Na+, O2-, F- - A) O2-, F-, Na+, Mg2+
,MCAT General Chemistry Questions exam
review
This is an isoelectronic series, which means that the number of electrons on each
ion is the same. In an isoelectronic series, the nuclear charge increases with
increasing atomic number and draws the electrons inward with greater force. The
ion with the fewest protons produces the weakest attractive force on the ions, so
it has the largest size. Oxygen has the smallest atomic number, so it has the fewest
protons, and therefore will have the greatest ion size.
Which of the following best explains why sulfur can make more bonds than
oxygen?
A) sulfur is more electronegative than oxygen
B) oxygen is more electronegative than sulfur
C) sulfur has 3d orbitals not available to oxygen
D) sulfur has fewer valence electrons - C) sulfur has 3d orbitals not available to
oxygen
Only elements in the third and higher periods of the periodic table can form more
than 4 bonds. Second period elements, including oxygen, have four valence
orbitals (one 2s and three 2p) with which to form bonds. By contrast, third period
elements like sulfur can form bonds with not only one 3s and three 3p, but also
five 3d orbitals. Remember that the second quantum number can have any
,MCAT General Chemistry Questions exam
review
integer value from 0 to n-1, so when n = 3, three subshells (s, p, and d) are
available.
Which of the following species has an unpaired electron in its ground-state
electronic configuration?
A) Ne
B) Ca+
C) Na+
D) O2- - B) Ca+
Atoms and ions with electron configurations identical to those of noble gases do
not have any unpaired electrons in their ground state. Ne, Na+, and O2- all have
the same electron configuration, [Ne], and therefore have no unpaired electrons
in their ground state. Ca+, by contrast, has a ground state configuration of [Ar]4s1,
and has one unpaired electron in its 4s subshell.
What is the electron configuration of chromium?
A) [Ar] 3d6
B) [Ar] 4s13d5
C) [Ar] 4s23d3
, MCAT General Chemistry Questions exam
review
D) [Ar] 4s24d4 - B) [Ar] 4s13d5
Even without pre-existing knowledge of the electron configuration of Cr, strongest
answer could have been identified by eliminating improbable choices. Choice C
can be eliminated because it has the wrong number of electrons. Choice D can be
eliminated because Cr ground state electrons exist in the 3d rather than 4d
subshell. Given Hund's rule, which states that the most stable arrangement of
electrons is the one with the most unpaired electrons, choice B might have
seemed more likely to be the best answer.
In reference to the photoelectric effect, which of the following will increase the
kinetic energy of a photoelectron?
A) increasing the work function
B) increasing the frequency of the incident light
C) increasing the number of photons in the incident light
D) increasing the mass of photons in the incident light - B) increasing the
frequency of the incident light
KE = hf - phi, in which h is Planck's constant, f is the frequency of incident light,
and phi is the work function of the metal. In other words, only the frequency of
the incident light and the work function of the metal affect the KE of ejected
review
Which of the following increases with increasing atomic number within a family
on the periodic table?
A) electronegativity
B) electron affinity
C) atomic radius
D) ionization energy - C) atomic radius
Only atomic radius increases going down a column. Size of an atom is determined
not only by effective nuclear charge, but also by number of electron shells.
Moving down a column, the number of electron shells increases. Because the
additional shells require additional space, atomic radius increases as number of
electron shells increases.
Which of the following most likely represents the correct order of ion size from
greatest to smallest?
A) O2-, F-, Na+, Mg2+
B) Mg2+, Na+, F-, O2-
C) Na+, Mg2+, O2-, F-
D) Mg2+, Na+, O2-, F- - A) O2-, F-, Na+, Mg2+
,MCAT General Chemistry Questions exam
review
This is an isoelectronic series, which means that the number of electrons on each
ion is the same. In an isoelectronic series, the nuclear charge increases with
increasing atomic number and draws the electrons inward with greater force. The
ion with the fewest protons produces the weakest attractive force on the ions, so
it has the largest size. Oxygen has the smallest atomic number, so it has the fewest
protons, and therefore will have the greatest ion size.
Which of the following best explains why sulfur can make more bonds than
oxygen?
A) sulfur is more electronegative than oxygen
B) oxygen is more electronegative than sulfur
C) sulfur has 3d orbitals not available to oxygen
D) sulfur has fewer valence electrons - C) sulfur has 3d orbitals not available to
oxygen
Only elements in the third and higher periods of the periodic table can form more
than 4 bonds. Second period elements, including oxygen, have four valence
orbitals (one 2s and three 2p) with which to form bonds. By contrast, third period
elements like sulfur can form bonds with not only one 3s and three 3p, but also
five 3d orbitals. Remember that the second quantum number can have any
,MCAT General Chemistry Questions exam
review
integer value from 0 to n-1, so when n = 3, three subshells (s, p, and d) are
available.
Which of the following species has an unpaired electron in its ground-state
electronic configuration?
A) Ne
B) Ca+
C) Na+
D) O2- - B) Ca+
Atoms and ions with electron configurations identical to those of noble gases do
not have any unpaired electrons in their ground state. Ne, Na+, and O2- all have
the same electron configuration, [Ne], and therefore have no unpaired electrons
in their ground state. Ca+, by contrast, has a ground state configuration of [Ar]4s1,
and has one unpaired electron in its 4s subshell.
What is the electron configuration of chromium?
A) [Ar] 3d6
B) [Ar] 4s13d5
C) [Ar] 4s23d3
, MCAT General Chemistry Questions exam
review
D) [Ar] 4s24d4 - B) [Ar] 4s13d5
Even without pre-existing knowledge of the electron configuration of Cr, strongest
answer could have been identified by eliminating improbable choices. Choice C
can be eliminated because it has the wrong number of electrons. Choice D can be
eliminated because Cr ground state electrons exist in the 3d rather than 4d
subshell. Given Hund's rule, which states that the most stable arrangement of
electrons is the one with the most unpaired electrons, choice B might have
seemed more likely to be the best answer.
In reference to the photoelectric effect, which of the following will increase the
kinetic energy of a photoelectron?
A) increasing the work function
B) increasing the frequency of the incident light
C) increasing the number of photons in the incident light
D) increasing the mass of photons in the incident light - B) increasing the
frequency of the incident light
KE = hf - phi, in which h is Planck's constant, f is the frequency of incident light,
and phi is the work function of the metal. In other words, only the frequency of
the incident light and the work function of the metal affect the KE of ejected
