CHEM 1101: CHEMISTRY (EEE/COE)
MODERN PERIODIC TABLE
Development of the Periodic Table:
People have known about elements like carbon and gold since ancient time. The elements
couldn't be changed using any chemical method. Each element has a unique number of
protons. If you examine samples of iron and silver, you can't tell how many protons the atoms
have. However, you can tell the elements apart because they have different properties. You
might notice there are more similarities between iron and silver than between iron and
The most important difference between Mendeleev's table and modern periodic table is that
modern table is organized by increasing atomic number, not increasing atomic weight. In
learned the atomic numbers (experimentally determine) of elements.
Before that, atomic numbers were just the order of elements based on increasing atomic
weight. Once atomic numbers had significance, the periodic table was reorganized.
Mendeleev's Statement of the Law of Periodicity
"The properties of the elements, as well
as the forms and properties of their compounds, are in periodic dependence on, or
form a periodic function of, the atomic weights of the elements."
Modern Statement of the Law of Periodicity (Moseley)
"The properties of the elements, as
well as the forms and properties of their compounds, are in periodic dependence on,
or form a periodic function of, the
of the elements."
Patterns in the Periodic Table: Main Features
The columns are called groups. The groups are divided into two sub groups: A and B.
These are numbered IA, IIA, IIIB, IVB, VB, VIB, VIIB, VIIIB, IB, IIB, IIIA, IVA,
VA, VIA, VIIA and VIIIA or 0 groups. The number of valence electrons equals the
Group number All the members of a Group have the same valence configuration but
different principal quantum numbers.
The rows are called periods (hence periodic table). There are seven periods in periodic
table. The period number equals the principal quantum number of the valence shell.
Group 1 is called The Alkali Metals.
Group 2 is called The Alkaline Earth Metals.
The middle portion, from group IB to VIIB is known as transition metal.
The inner transition metals are at the bottom- lanthanides and actinides.
Group 7 is called the Halogens.
Group zero is called the Noble Gases/ Inert Gases.
Hydrogen occupies a unique position at the top of the periodic table. It does not fit
naturally into any Group.
The elements in group VIIIB consist of three groups of elements at the middle of the
Course-Teacher: Shahrina Alam