TRENDS in the PERIODIC TABLE
A trend is a pattern Trends of the
or a repetition of periodic table
Net Nuclear Charge,
Metallic or Non-Metallic
1st ionization energy
The periodic table
in a certain way
to keep elements with
similar properties close
GROUPS vs. PERIODS
Groups go up and down.
Periods go left and right.
Groups share many similarities.
Periods show periodically
(regularly) changing properties.
The Periodic Table
has a lot of
information on it,
available for you to
use, if you know
where to look and
what it all means.
are your friends,
play with them.
SEVERAL BASIC TRENDS
THAT WE NEED TO
These Trends are…
1. Atomic Mass (in amu)
2. Atomic Radius (size in picometers)
3. Net Nuclear Charge
(how many protons are in the nucleus of an atom?)
4. Ion Size (cations and anions)
5. Metal Properties and Non Metallic Properties
7. 1st Ionization Energy levels
• Developed the first
real periodic table
which ours is based
• He was able to
predict the missing
elements and their
properties once the
table was put
Mendeelev was a genius!
Many of his predictions came true, such as the existence of
“eka-aluminum” which we know as gallium.
A missing element in his table made him believe that an
element with certain properties belonged there.
By looking specifically for this missing
chemists were able to discover gallium.
His predictions were quite close to the actual values of the
various properties he quoted, such as mass, density, ionic
formula, and others.
Our FIRST Trend
Atomic mass goes higher from element
to element, with few exceptions.
The Group Trend is that atomic
The Period Trend is that atomic
mass increases too.
Because of specific properties...
our Periodic Table has a non-regular shape.
The elements are arranged by properties rather than a
way just make the table be uniform in shape.
The Alkali Metals
are in Group 1 but Hydrogen is not in this group.
Alkaline Earth Metals
are in Group 2
This slide left intentionally
blank, and you know why.
are in Groups 3 - 12
are at the bottom and fit in as shown
are at the right hand side of the table
are at the far right, group 18
OUR SECOND TREND
Atomic Radius or Atom Size
If you follow along Table S
for atomic radius, you find:
The Group Trend for atomic
radius is that it increases
down a group.
The Period Trend for atomic
radius is that it decreases
left to right.
Period Trend for Atomic Radius
Li Be B C N O F Ne
2-1 2-2 2-3 2-4 2-5 2-6 2-7 2-8
•• • • • • • •
Atoms get smaller as you go across a period.
They gain electrons in the same energy levels, not getting bigger.
The additional positive charge from the additional protons pulls the
electron orbital slightly tighter for each atom going across the period.
SHOWS Atomic Sizes for Groups and Periods
This is too easy to even discuss much. Hold onto your hat, and be psyched
that this is “REQUIRED” learning.
Each atom is neutral because it has the SAME number of protons & electrons.
Electrons fly around outside the nucleus in orbitals. Protons hang tight
(no joke) with the neutrons in the nucleus. Since the neutrons are neutral
(hence their name!), the only charge particles in the nucleus are the protons,
which are ALL POSITIVE. So, the NET NUCLEAR CHARGE is how many
protons are there in the nucleus, and since each is positively charged, that is
Example: Mercury is number 80, with 80 electrons and 80 protons, a neutral
atom. It also has 121 neutral neutrons in the nucleus with the 80 protons.
So, NET nuclear charge = +80.
Someone, somehow, determined that “the most metallic metal” was
Francium, bottom left hand corner of the Periodic Table.
They also came to the conclusion that Helium was to become
known as the “most non-metallic” element.
You have to remember that, and you have to be able to compare up
to 4 elements at a time and see which is closer to either Fr or He,
and decide which is the most metallic, or most non-metallic.
The NEXT TREND is
1st IONIZATION ENERGY
[what the heck was that again?]
First Ionization Energy,
It is the amount of energy needed to remove
a valence electron from an entire mole of atoms
and make them all into +1 ions.
To turn a mole of Li atoms
into a mole of Li+1 ions,
it would take (look at Table S now)
FIRST IONIZATION ENERGY
the units are kilo-Joules per mole or kJ/mole
There is a whole list of them
on your TABLE S,
Please get Table S out now.
Look at Table S, find Sodium
• Na has a first ionization energy of 496 kJ/mol
• That means to take an outer electron from an
entire mole of sodium atoms, making each one
of those Avogadro’s Number of atoms into a
Na+ ion, it would take 496 kJ for the mole.
FIRST IONIZATION Going across the 3rd
ENERGY FOR SOME period, the trend for
SELECTED ATOMS 1st Ionization Energy
Na 496 kJ/mol is to INCREASE.
Mg 736 kJ/mol
what about Mg
Al 578 kJ/mol to Al then???
Si 787 kJ/mol
P 1012 kJ/mol
The Mg - Al EXCEPTION
is one of those unusual
places where the periodic
table cannot manage to be
Still, “the trend” is that first It’s a trend to wear a
tuxedo to the high
ionization energy increases school prom. But it’s an
when going across any exception to wear a
color like these guys!
• just so you know, there are first, second
and third ionization energy levels.
• each is measured with the unit kJ/mol
• the “first” is the energy required to
remove the first electron
• the “second” is to remove an additional
electron from the mole of ions (+1
cations into +2 cations, this is not in
Another Trend – Ionic Sizes
Atomic size • Cations are always smaller than
atoms because the cations lose
a whole orbital when they form.
• atoms get
down a • Anions are bigger than the atoms
group they started as, because by
adding electrons into the outer
• atoms get orbital, they must stretch a bit
smaller larger to accommodate those
going across extra negative charges that push
a period against each other.
Cs +1 is larger than K+1
Br-1 is bigger than Cl
when going down a group
the ions get bigger
Cs+1 This is true for
cations & anions
GOING ACROSS A PERIOD
CATION S get smaller
ANIONS get smaller too.
TABLE S in your reference charts
has all the data about 1st ionization energy levels,
and about atomic sizes and about the last trend that
we’ll cover - electro-negativity.
If you forget the trend, pick a few atoms and
put the numbers onto your periodic table
and show yourself the trend.
Be sure to use a few though in case you pick a
quirky exception (like the Mg to Al bump
in 1st ionization energy.
DO NOT MEMORIZE, think.
Say it to yourself a few times in your head.
It’s a really cool word and you are going to know it real
soon too. Impress your friends with new sayings like:
“Your electro-negativity is really getting on my nerves.”
“My goodness! I can feel your electro-negativity all
the way over here!”
the measure of the attraction an
atom has to gain an electron
in a chemical reaction.
It’s measured on the
Linus Pauling electro-negativity scale.
Fluorine and E-N
• Fluorine tops out the
scale at 4.0
• Pauling set this standard,
because he could.
• It’s a totally arbitrary
scale, based upon
Fluorine and at 4.0 just
because. All other atoms
are compared to that
• All the other electro-
negativity values are
relative to Fluorine’s
Dr. Linus Pauling
That’s him at age 2.
Because of his dynamic personality and his many
accomplishments in widely diverse fields, it is hard to define
Linus Pauling adequately. A remarkable man who insistently
addressed certain crucial human problems while pursuing an
amazing array of scientific interests, Dr. Pauling was almost
as well known to the American public as he was to the
world's scientific community. He is the only person ever to
receive two unshared Nobel Prizes, one for
Chemistry (1954) and for Peace (1962).
the importance of
having a full and
To have met this man must have been
happy personal life. quite an honor, he would have made
a fine guest for dinner.
In addition to the general recognition as one of the two
greatest scientists of the 20th century, he was usually
acknowledged by his colleagues as the most influential
chemist since Lavoisier, the 18th-century founder of the
modern science of chemistry.
His introductory textbook General Chemistry, revised three
times since its first printing in 1947.
Electro-negativity is the amount of pull that
an atom has for another electron in a bonding
situation. Fluorine has the greatest desire of
all atoms for that electron gain. Fluorine is
given the rating of 4.0 on the E-N scale, the
highest Electronegativity of all elements.
Electro-negativity is on Table S. You don’t have to memorize
the trend, you can look it up anytime you want to.
• Going down • Going across a
a group the period the trend
trend is towards is towards higher
It is all about HOW CLOSE IS THE ATOM TO FLUORINE
which determines the relative electro-negativity.
Trends are just trends,
they do not ALWAYS hold true.
Use your Table S to determine trends,
do not guess or foolishly try to memorize
so much material when the answers
are right in your hand.
READ CHAPTER 14 ASAP