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University of South Carolina-Columbia
CHEM 333 Chem 121A: Periodic Trends,
Bonding, and Geometry Questions and
Answers 2026 Latest Update
effective nuclear charge (Zeff) Ans: The net pull the nucleus has on valence
electrons. Calculated as Zeff = protons - inner (core) electrons.
trend for Zeff across a period Ans: Zeff increases across a period (left to
right) because more protons are added.
atomic size across a period Ans: Atomic size decreases. More protons pull
electrons in closer.
atomic size down a group Ans: Atomic size increases. More electron shells
are added.
cations compared in size to their atoms Ans: Cations are smaller than the
neutral atom—they lose electrons.
anions compared in size to their atoms Ans: Anions are larger than the
neutral atom—they gain electrons.
ionization energy Ans: Energy needed to remove an electron from an atom.
trend for ionization energy across a period Ans: It increases across a period
(harder to remove electrons).
trend for ionization energy down a group Ans: It decreases down a group
(easier to remove electrons).
electron affinity Ans: Energy change when an atom gains an electron.
do all atoms release energy when gaining electrons? Ans: Most do, but not
all—some have positive electron affinity.
© 2026 All rights reserved
University of South Carolina-Columbia
CHEM 333 Chem 121A: Periodic Trends,
Bonding, and Geometry Questions and
Answers 2026 Latest Update
effective nuclear charge (Zeff) Ans: The net pull the nucleus has on valence
electrons. Calculated as Zeff = protons - inner (core) electrons.
trend for Zeff across a period Ans: Zeff increases across a period (left to
right) because more protons are added.
atomic size across a period Ans: Atomic size decreases. More protons pull
electrons in closer.
atomic size down a group Ans: Atomic size increases. More electron shells
are added.
cations compared in size to their atoms Ans: Cations are smaller than the
neutral atom—they lose electrons.
anions compared in size to their atoms Ans: Anions are larger than the
neutral atom—they gain electrons.
ionization energy Ans: Energy needed to remove an electron from an atom.
trend for ionization energy across a period Ans: It increases across a period
(harder to remove electrons).
trend for ionization energy down a group Ans: It decreases down a group
(easier to remove electrons).
electron affinity Ans: Energy change when an atom gains an electron.
do all atoms release energy when gaining electrons? Ans: Most do, but not
all—some have positive electron affinity.
© 2026 All rights reserved
