Chemical Periodicity
Chapter 5
Periodic Trends in Atomic Size
Periodic Trends in Ionization
Energy
Periodic Trends in Ionic Size
Periodic Trends in
Electronegativity
Periodic Trends in Atomic Size
The boundary of an atom can't
be measured directly
Atomic Radius: half the distance
between nuclei of two like
atoms.
Write the Electron Configuration for
Li, K and F
Look at the position of these elements on the
Periodic Table. Can you detect a “trend” in size
as you go down a group?
What do you think the trend is going
across a period?
Periodic Trends in Atomic Size
Atomic size increases down a group
– What happens to the energy level as we go
down a group? Where are the electrons?
Atomic size decreases from left to right
– Where are the electrons?
– the nucleus has more attraction to the electrons
Periodic Trends in Atomic Size
Which would be
bigger?
a. Sodium or Aluminum
b. Magnesium or Barium
c. Nickel or Bromine
d. Calcium or Yttrium
e. Describe in your own words why
atoms in the same period decrease in size
from left to right.
Periodic Trends in Ionization
Energy
Ionization Energy:
– Energy required to
overcome the attraction of
the nucleus and remove an
electron.
Draw a Bohr model for
Li, Na and N and F
Ionization energy decreases as you move down
a group because electrons are further away so
they are easier to strip off.
Ionization energy increases as you move left to
right, for representative elements because the
attraction by the nucleus is stronger so it is
harder to pull electrons away.
Ionization Energy Graph
Graph the data listed on the Table of
ionization energies.
Graph the Atomic number on the x-axis
(1 thru 22)
Graph the ionization energy on the y-axis
(0 thru 160)
What trend do you see?
Look at the
Table of Ionization Energies
First ionization energy- energy necessary to
remove the 1st electron
Second ionization energy- energy necessary
to remove the 2nd electron.
Third ionization energy- energy necessary to
remove the 3rd electron.
Periodic Trends in Ionization
Energy
Trends in Electron Affinity
The energy change that occurs when an
atom gains an electron.
Let’s look at Li and F AGAIN
Which one wants to gain an electron?
It would have a high electron affinity
Electron Affinity-most atoms release energy
when gaining an electron
(explains the negative sign)
Li
-61.8 kJ/mol
F
-340 kJ/mol
Have to force the atom
to take the electron.
Energy absorbed
Low affinity
Gains electrons easily
Energy is released
High affinity
Trend in Electron Affinity
Periodic Trends in Ionic Size
Let’s look at Li and F again.
If each atom wants to achieve a full outer
energy level (full octet)…. What has to
happen to the electrons?
When they gain or lose electrons, what do
they become?
What happens to the size of the atom?
Periodic Trends in Ionic Size
Anions are atoms that have gained electrons
and have an overall negative charge.
Anions are larger than the atoms from which
they have formed.
Why?
Cations are atoms that have lost an
electron and have an overall positive
charge.
Cations are smaller than the atom from
which they have formed.
Check it out!
Periodic Trends in Ionic Size
Cations decrease in the
size from left to right.
Anions decrease in size
from left to right
As you move down a
group the radius
increases because of
more electrons in
higher energy levels
Warm Up
Which atom is the largest?
Mg or Mg2+
O or O2Cu2+ or Cu4+
Write a rule that will help you get
these right every time!
Let’s go over some homework!
Isoelectronic
Na1+, Ne and F1- are said to be
Isoelectronic.
a. Determine the electron configuration for
each of the atoms
b. Define isoelectronic
Isoelectronic
1. Write a 2- ion that is isoelectronic with Mg2+
2. Write 3 ions that are isoelectronic with Kr
3. Write 2 ions that are isoelectonic with Ni
Trends in Electronegativity
Electronegativity:
– The tendency of an element to attract
electrons when in a chemical bond.
Let’s look at Li, Cs and F
Warm Up: In CB
Which is more electronegative? Use the
trend, then check them using the table.
Al or Cl?
Ca or Ba?
Ga or S
I or Cl?
W or Zn?
Element Reactivity
What would make an element reactive?
Which elements are most reactive?
What would make an element unreactive?
Which elements would be most
unreactive?
Let’s look at your table of
electronegativities.
Electronegativity table:
– Noble gases are left out because they do
not form compounds.
– Metals have low electronegativity numbers
because they want to give electrons away,
not attract them.
– Nonmetals have high electronegativity
numbers because they attract electrons to
make their configurations more stable
Trends in Electronegativity
Relationship Between
Electronegativity and Ionization
Energy
Moving left to right, the representative
elements, electronegativity increases
because ionization energy increases
Moving down a group electronegativity
decreases because ionization energy
decreases
Warm Up- Fill in the following table
(p.159 may help)
Atom
P
Rb
Cl
Be
Al
Metal or
nonmetal?
Stable ion
Size relative
to neutral
atom
Larger or
smaller than
S2-
How did you do?
Atom
Metal or
nonmetal?
Stable ion
Size relative
to neutral
atom
Larger or
smaller than
S2-
P
nm
P3-
larger
larger
Rb
m
Rb1+
smaller
smaller
Cl
nm
Cl1-
larger
smaller
Be
m
Be2+
smaller
smaller
Al
m
Al3+
smaller
smaller
Let’s practice some EC
Al3+
C4-