Transcript AP Chemistry Chapter 7

Periodic Trends
Atomic Radius
Definition: Half of the distance
between nuclei in covalently bonded
diatomic molecule
Radius decreases across a period
 Increased effective nuclear charge
due to decreased shielding
Radius increases down a group
 Each row on the periodic table adds
a “shell” or energy level to the atom
Table of
Atomic
Radii
Period Trend:
Atomic Radius
Ionization Energy
Definition: the energy required to remove an
electron from an atom
 Increases for successive electrons taken from
the same atom
Tends to increase across a period
 Electrons in the same quantum level do not
shield as effectively as electrons in inner levels
 Irregularities at half filled and filled
sublevels due to extra repulsion of electrons
paired in orbitals, making them easier to
remove
 Tends to decrease down a group
 Outer electrons are farther from the
nucleus and easier to remove
Ionization Energy: the energy required to
remove an electron from an atom
 Increases for successive electrons taken from the
same atom
 Tends to increase across a period
Electrons in the same quantum level do not
shield as effectively as electrons in inner
levels
Irregularities at half filled and filled
sublevels due to extra repulsion of electrons
paired in orbitals, making them easier to
remove
 Tends to decrease down a group
Outer electrons are farther from the nucleus
Table of 1st Ionization
Energies
Periodic Trend:
Ionization Energy
Electron Affinity
Definition - the energy change associated
with the addition of an electron
 Affinity tends to increase across a period
 Affinity tends to decrease as you go
down in a period
Electrons farther from the nucleus
experience less nuclear attraction
Some irregularities due to repulsive
forces in the relatively small p
orbitals
Periodic Trend:
Electron Affinity
Electronegativity
Definition: A measure of the ability of an
atom in a chemical compound to attract
electrons
o Electronegativity tends to increase
across a period
o As radius decreases, electrons get
closer to the bonding atom’s nucleus
o Electronegativity tends to decrease
down a group or remain the same
o As radius increases, electrons are
farther from the bonding atom’s
nucleus
Periodic Table of Electronegativities
Periodic Trend:
Electronegativity
Summary of
Periodic Trends
Ionic Radii
Cations
 Positively charged ions formed when
an atom of a metal loses one or
more electrons
 Smaller than the corresponding
atom
 Negatively charged ions formed
when nonmetallic atoms gain one
Anions
or more electrons
 Larger than the corresponding
atom
Table
of Ion
Sizes