AP Chemistry
Chapter 6 Notes
Periodic Law – properties of the
elements are a periodic function
of their atomic number
The moon’s phases
and magazine
subscriptions are
also periodic…
The earliest and most
successful
arrangement of the
elements was by Dmetri
Mendeleev in the 1870s.
He arranged the
elements known at that
time by their physical
and chemical
properties into groups.
His arrangements of the elements
left some gaps, which he claimed
were elements not yet discovered.
With his table he predicted the
characteristics of these missing
elements, and was correct.
During the 1910s,
Henry Moseley used
x-ray spectra to
determine the atomic
number (number of
protons) for
elements and proved
that each element
had a different
amount of protons.
Moseley rearranged the elements
based on atomic number, as it is
arranged today, and found gaps
which he also claimed were
undiscovered elements. Some of
these elements were found
quickly, while others were not
found until after his death due to
their highly radioactive (unstable)
nature.
There are three key items in
understanding and explaining all
the trends (and exceptions) on the
periodic table.
There are three key items in
understanding and explaining all
the trends (and exceptions) on the
periodic table.
1. Effective Nuclear Charge
There are three key items in
understanding and explaining all
the trends (and exceptions) on the
periodic table.
1. Effective Nuclear Charge
2. Energy Levels
There are three key items in
understanding and explaining all
the trends (and exceptions) on the
periodic table.
1. Effective Nuclear Charge
2. Energy Levels
3. Coulombs Law
1. Effective Nuclear Charge – pull
of the protons in the nucleus on
the valence (outer) energy level
electrons
1. Effective Nuclear Charge – pull
of the protons in the nucleus on
the valence (outer) energy level
electrons
The greater the atomic number, the
greater the number of protons,
and the greater the effective
nuclear charge.
Effective Nuclear Charge has the
greatest effect moving from left to
right across a period (it
increases).
Effective Nuclear Charge has the
greatest effect moving from left to
right across a period (it
increases).
Which element has more effective
nuclear charge, P or S?
Effective Nuclear Charge has the
greatest effect moving from left to
right across a period (it
increases).
Which element has more effective
nuclear charge, P or S?
Which element has more effective
nuclear charge, S or Se? (Why
won’t this work?)
2. Energy levels - the principal
quantum level of the electrons,
sometimes called shells
2. Energy levels - the principal
quantum level of the electrons,
sometimes called shells
As elements increase in atomic
number they also increase in the
number of electrons. These
electrons occupy higher and
higher energy levels.
Higher numbered energy levels are
farther away from the nucleus.
1s
1s
2s
1s
2s
3s
Energy Levels have the greatest
effect moving from top to bottom
within a group (it increases).
Energy Levels have the greatest
effect moving from top to bottom
within a group (it increases).
Which element has more energy
levels, S or Se?
Energy Levels have the greatest
effect moving from top to bottom
within a group (it increases).
Which element has more energy
levels, S or Se?
Which element has more energy
levels, P or S? (Why won’t this
work?)
3. Coulombs Law states that the
force of attraction between things
is directly proportional to the size
of the charge and inversely
proportional to the square of the
distance between them.
What two things are attracted to
each other in an atom?
What two things are attracted to
each other in an atom?
Which one can move?
Which situation would show the
stronger force of attraction?
Explain.
2p+
12p+
1e-
1e-
Which situation would show the
stronger force of attraction?
Explain.
2p+
2p+
1e-
1e-
For the following trends, you must
know the general trends
(memorize), but using the three
key items you must be able to
explain the trend as well
(understand).
1. Atomic Radius
size of the atom
a. increases from top to bottom
within a group
Why does it increase from top to
bottom?
1. Atomic Radius
size of the atom
b. decreases from left to right
within a period
Why does it decrease from left to
right?
2. Ionization Energy
energy required to remove an
electron from a gaseous atom
a. increases bottom to top
Why is it easier to remove
electrons from atoms at the
bottom of the P.T.?
2. Ionization Energy
energy required to remove an
electron from a gaseous atom
b. increases left to right
Why is it easier to remove
electrons from atoms at the left
of the P.T.?
2. Ionization Energy
energy required to remove an
electron from a gaseous atom
c. This is sometimes called
metallic character, as metals
tend to lose electrons easily.
Which element would exhibit the
most metallic character?
3. Electron Affinity
energy released when an
electron is added to a gaseous
atom
a. increases bottom to top
Why is more energy released when
electrons are added to atoms at
the top of the P.T.?
3. Electron Affinity
energy released when an
electron is added to a gaseous
atom
b. increases left to right
Why is more energy released when
electrons are added to atoms at
the right of the P.T.?
3. Electron Affinity
energy released when an
electron is added to a gaseous
atom
c. This is sometimes called
nonmetallic character, as
nonmetals tend to gain
electrons easily.
Which element would exhibit the
most nonmetallic character?
4. Electronegativity
measure of an atom’s pull on
another atom’s electrons
a. increases bottom to top
Why are atoms at the top of the P.T.
able to pull stronger on a
different atom’s electrons?
4. Electronegativity
measure of an atom’s pull on
another atom’s electrons
b. increases left to right
Why are atoms at the right of the
P.T. able to pull stronger on a
different atom’s electrons?
5. ions
charged atoms
a. cations – positive ion formed
from an atom losing an electron
The ionic radius is always smaller
than the original atom.
Why?
5. ions
charged atoms
b. anions – negative ion formed
from an atom gaining an electron
The ionic radius is always larger
than the original atom.
Why?
Let’s summarize the trends.
Remember you must know the
trend (memorize) but you also
need to be able to explain why
the trend exists.
Atomic Radius
Ionization Energy, Electron Affinity, Electronegativity
Energy Levels
Effective Nuclear Charge
Metallic Character
Nonmetallic Character