Transcript Periodic Trends

Periodic Trends
Chapter 6
Section 3
Atomic radius

Electron clouds do not have clearly defined
edges.

Atomic size is defined by how closely an atom
lies to a neighboring atom.
Trends within periods
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In general, there is a decrease in atomic radii
as you move left-to-right across a period.
It’s caused by an increasing positive charge in
the nucleus and the fact that the principal
energy level within a period remains the same.
Increased nuclear charge pulls outermost ecloser.
Trends within groups

Atomic radii generally increase as you move
down a group.
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The nuclear charge increases and e- are added
to successively higher principal energy levels.

Inner e- orbitals shield outer e-.
www.avon-chemistry.com
Ionic Radius
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An ion is an atom or a bonded group of atoms
that ha a positive or negative charge.
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When atoms lose e- and form positively
charged ions, they always become smaller.
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Na
Na+
Ionic Radius (cont.)
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When atoms gain e- and form negatively
charged ions, they always become larger.
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S
S2-
Trends within periods and groups
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Elements on the left side form cations and
elements on the right form anions.
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As you move from left-to-right, the ionic
radius decreases.

As you move down a group, there is a gradual
increase in ionic size.
www.public.asu.edu
Ionization Energy
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Ionization energy is defined as the energy
required to remove an e- from a gaseous atom.
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The loss of an electron results in an ion.
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It’s an indication of how strongly an atom’s
nucleus holds onto its valence e-.
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Ionization Energy
(cont.)
st
After removing the 1 e-, it is possible to
remove additional e-. (First ionization energy)
www.britannica.com
Trends within periods

First ionization energies generally increase as
you move from left-to-right across a period.

Increased nuclear charge has an increased hold
on valence e-.
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Related to atomic radius decrease.
Trends within groups

First ionization energies generally decrease as
you move down a group.
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Valence e- are farther from the nucleus
because atomic radius increases.

The octet rule states that atoms tend to gain,
lose or share e- in order to acquire a full set of
eight valence e-.
Electronegativity
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The electronegativity of an element indicates
the relative ability of its atoms to attract e- in a
chemical bond.
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F is the most electronegative element.
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Electronegativity generally decreases as you
move down a group and increases as you move
left-to-right across a period.
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