If all the elements are arranged in the order of their atomic weights, a periodic repetition of properties is obtained. This is expressed by the law of periodicity.— Dmitry Ivanovich Mendeleev

1. The Wonders of Periodic Table
Prof. Liwayway Memije-Cruz

2. Periodic Table
Periodic Table is the tabular arrangement of all the
chemical elements which are organized based on
atomic numbers, electronic configurations and
existing chemical properties.

3. Development of Periodic Table
As early as 1800, chemists
began to determine the atomic
weights of some elements with
fair accuracy. Several attempts
were made to classify the
elements on this basis.

4. State of the Environment:
Issues and Concerns
Johann Wolfgang Dobereiner
He classified the
elements in groups of 3
called triads, based on
similarities in properties
and that the atomic
mass of the middle
member of the triad was
approximately the
average of the atomic
masses of the lightest
elements.

5. John A. Newlands (1863)
He arranged the
elements in the order of
increasing atomic mass.
The eight elements
starting from a given
one is a kind of
repetition of the first like
the eight notes of the
octave of music and
called it the law of
octaves.

6. Lothar Meyer
He plotted a
graph showing
an attempt to
group elements
according to
atomic weight.

7. Dmitri Mendeleyeev (1869)
 He worked out a
Periodic Table of
Elements were the
elements were
arranged in the order
of increasing atomic
weights with a regular
repetition (periodicity)
of physical and
chemical properties.

8. Henry Moseley
 He arranged the
elements in the order of
increasing atomic
numbers, which relates
that the properties of the
elements are periodic
functions of their atomic
numbers. This is known
as the Modern Periodic
Law.

9. 1. Representative Elements are the elements in A Group/ Family. The term
representative element is related to stepwise addition of electrons to the s and p
sub levels of the atoms. Elements belonging to the same group or family have
similar properties.
2. Noble Gases or Inert Gases are the elements in the last group with completely filled
set of s and p orbitals.
3. Transition Elements are the elements in the columns IB - VIIIB which are called the
B Group/Family. Take note that they start with IIB up to VIIB, which have 3
columns and then end with IB and IIB. These sequences, which contain 10
elements each, are related to the stepwise addition of the 10 electrons to the d
sub level of the atoms. These elements are metallic-dense, lustrous, good
conductor of heat and electricity and in the most cases are hard. They form the
many colored compounds and form polyatomic ions like Mn04 and CrO4.
4. Inner Transition Elements are the 2 additional horizontal rows below composed of 2
groups of elements which were discovered to have similar characteristics as
Lanthanum in the 6th
period called Lathanoids (Rare Earth Metals) and Actinium
(Heavy Rare Elements). The Lanthanoids are all metals while the Actinoids are all
radioactive. All the elements after Uranium are produced artificially by nuclear
reactions.
Classification of elements in the
Periodic Table

10. Positions of metals, nonmetals and
metalloids in the Periodic Table
Metals are at the left and in the center of the Periodic Table. Atoms of
metals tend to donate electrons.
Nonmetals are at the far right and toward the top of the Periodic Table.
Atoms of non-metals tend to accept electrons.
Metalloids or borderline elements are elements that to some extent
exhibit both metallic and nonmetallic properties. They usually act as
electron donor with metals and electron acceptor with non-metals. These
elements lie in the zigzag line in the Periodic Table.

11. Atomic size

12. Exercise:
Consider the atoms of Period 3:
 Na 2e 8e 1e Mg 2e 8e 2e Al 2e 8e 3e
Consider the electronic configuration of Group IA
elements:
 Na 2e 8e 1e
 K 2e 8e 8e 1e
 Rb 2e 8e 18e 8e 1e
 Cs 2e 8e 18e 18e 8e 1e
 Fr 2e 8e 18e 18e 18e 8e 1e

13. When an atom losses or gains electron, it becomes a
positively/negatively charge particle called ion.

14. Ionization energy is the amount of energy required to remove the most
loosely bound electron in a gaseous atom or ion to give a positive (+) particle
of cation.
Going across a period, there is an increase in the
ionization energy due to the removal of electron in each
case is at the same level and there is a greater nuclear
charge holding the electron.

15. Electron affinity is the energy given off when a neutral gaseous
atom or ion takes in an electron. Negative ions or anions are formed.

16. Electronegativity is the tendency of an atom to attract shared
electrons to itself when it forms a chemical bond with another atom.

17. Summary of the Trends in the Periodic
Table