Transcript Periodicity

Periodicity
E.Q.: What information can be obtained from the
periodic table and how is it used?
Hypothesize (Face Partners)
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How do valence electrons change as you go:
a) Across a period - (increases, decreases, stays the
same)
b) Down a group - (increases, decreases, stays the
same)
How does ionization energy change as you go:
a) Across a period - (increases, decreases, stays the
same)
b) Down a group - (increases, decreases, stays the
same)
How does atomic radius change as you go:
a) Across a period - (increases, decreases, stays the
same)
b) Down a group - (increases, decreases, stays the
same)
Periodicity
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Atomic radius
Ionization energy
Electronegativity
Metallic character
Atomic radius
• One half the distance between the nuclei of
identical atoms that are bonded together.
• Atoms shrink as you advance across a
period because added protons in the nucleus
pull the added electrons more tightly in the
absence of effective shielding.
• Atoms in the same column increase in size
as you go down the family since electrons
are being added on successively higher
energy levels and are well shielded by the
previous completed electron energy levels.
ATOMIC RADIUS
As you move from left to right across a period, more protons (atomic number
increases) are present in the nuclei of atoms and they can pull-in the
electrons closer to the nucleus thus shrinking the radius of the atom.
ATOMIC RADIUS
As you move from top to bottom down a column, atomic number increases
but also the number of energy levels increases and it becomes much harder
for the protons to pull-in the electrons in the outer energy levels (effective
shielding). Thus atomic radius increases.
ATOMIC RADIUS INCREASES
ATOMIC RADIUS DECREASES
Atomic radius
• Radius (or size):
– Decreases from left to right (across periods)
– Increases from top to bottom (within a family)
ATOMIC RADIUS
In other words……..atomic radius
increases in the direction of the
arrow!
IONIZATION ENERGY
• Ion: An atom of an element that has lost or
gained an electron/s and now has gained a
positive or negative charge (no longer
neutral).
• It takes energy to remove an electron.
Ionization Energy
• Amount of energy required to remove an electron
from an atom.
• The outer-most electron becomes increasingly more difficult
to remove as you advance across a period since shielding is
very poor and the added protons continue to exert a
stronger attraction.
• The outer-most electron is easier to remove as you move
down a column since each time you are one energy level
farther from the nucleus, benefiting from that much more
shielding.
IONIZATION ENERGY DECREASES
IONIZATION ENERGY INCREASES
Electronegativity
• The ability of a bonded atom to attract the electrons
in that bond.
• As you move across a period from left to right,
atoms are able to attract electrons since shielding
is ineffective and protons in nuclei can attract
electrons from other atoms of different elements.
Electronegativity increases.
• As you move down a group, number of energy
levels increases and it becomes more difficult for
the nuclei to hold on to the outermost electrons.
Electronegativity decreases.
ELECTRONEGATIVITY DECREASES
ELECTRONEGATIVITY INCREASES
Metallic character
Metallic properties are related to the freedom
of the outer electrons to move in a
macroscopic sample and thus these
properties are most pronounced at the left
side of the table where shielding is at a
maximum.
• This means that metallic properties will also
increase as you move down a family since
shielding improves.
Metallic character
Fr (Francium) is the most reactive metal.
F (Fluorine) is the most reactive non-metal.
The noble gases are very un-reactive.
Summary of Periodic Trends
Atomic radius metallic
character increase
Electronegativity and
Ionization energy increase
Summary of Periodic Trends
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Conclusions
Valence electrons:
a) Across a period - (increases)
b) Down a group - (stays the same)
• Ionization energy:
a) Across a period - (increases)
b) Down a group - (decreases)
• Atomic radius:
a) Across a period - (decreases)
b) Down a group - (increases)