trends by xiaohuicaicai


									 TRENDS in the PERIODIC TABLE
A trend is a pattern     Trends of the
or a repetition of       periodic table
                        Atomic Mass,
                       Atomic Radius,
                    Net Nuclear Charge,
                           Ion Size,
                   Metallic or Non-Metallic
                    1st ionization energy
   The periodic table
       is arranged
    in a certain way
to keep elements with
similar properties close
   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.

The Regents
Reference Charts
are your friends,
play with them.
     (or patterns)
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
6. Electronegativity
7. 1st Ionization Energy levels
Demetri Mendeelev
       • 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
Atomic mass goes higher from element
 to element, with few exceptions.
The Group Trend is that atomic
 mass increases.
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
Noble Gases
 are at the far right, group 18
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
the answer.
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

[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.
                  For example…
          To turn a mole of Li atoms
           into a mole of Li+1 ions,
           it would take (look at Table S now)

                   520 kJ/mole
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
is one of those unusual
places where the periodic
table cannot manage to be
perfect for
all properties.
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!
         Ionization Energy
• 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
  Regents Chemistry.)
    Another Trend – Ionic Sizes
Atomic size      • Cations are always smaller than
                   atoms because the cations lose
                   a whole orbital when they form.
• atoms get
  bigger going
  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

Cs+1        This is true for
           cations & anions

  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).
Linus Pauling
always emphasized
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
                             E-N values.
    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.


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