Showing posts with the label Periodic Table


Methanal or the saturated aqueous solution of formaldehyde (40% by volume, 37% by weight) is known as 100% formalin which is mainly used to preserve dead animals.

Modern Periodic Law

The modern periodic law is as follows: In the periodic table, the physical and chemical properties of the elements repeat periodically with their atomic number depending upon the electronic arrangement of the elements.

Electron Configuration

Electron configuration is the distribution of electrons in various shells for any element. Such as electron configuration of Al is- Al(13)→ 2, 8, 3

The first law of Mendeleev

Arranging the elements based on their molecular weight, their physical and chemical properties are noticed to periodically reoccur.


Around the nucleus there are some circular stable axis on which electron moves around. These are called energy level or orbit.


Atoms of the same element having different mass number are called isotopes of each other.

Valence Electron

The electrons at the outermost principal energy level of an element are called the valence electron of that element.

Periodic property

The change of material property with the successive change of period and group in the periodic table is termed as the periodicity of elements.


The tendency of solid, liquid or gas to spread spontaneously and uniformly in any medium is called diffusion.

Formula of Periodicity

Chemical and physical properties of elements return periodically, in the periodic table after a certain period. This formula is called formula of periodicity.


A mixture contains more than one substance. The substances are just mixed together, and not chemically combined. For example:   air is a mixture of nitrogen, oxygen, and small amounts of other gases  shampoo is a mixture of several chemicals and water.

Basis of Periodic Table

The fundamental basis of the periodic table is electronic configurations of the elements.

Periodic properties of elements

Any period in the periodic table has got the most metallic on the left and gradually elements are less metallic as the period extends to the right. The more a period progresses from left to right the size of atom or atomic radius decreases. The more a period progresses from left to right, the value of ionization energy decreases. The more a period progresses from left to right the value of electron affinity increases. The more a period progresses from left to right the value of electronegativity increases.

Characteristics of Periodic Table

There are a total of 118 elements, 7 periods and 18 groups arranged in the periodic table. Group-1 elements are Alkali metals, Group-2 elements are Alkaline earth metals, Group-11 elements are coin metals, Group-16 elements are called Chalcogen, Group-17 elements are Halogen and elements belonging to group-18 are called inert gas. 15 elements with atomic numbers 57-71 are called the Lanthanide elements. Fifteen elements with atomic numbers 89-103 are categorized as Actinide elements

Background of Periodic Table

In 1789, Antoine Lavoisier first divided the elements metals and non-metals In 1829, the scientist Dobereiner found Law of Triads. In 1864, John A R Newlands gave a theory called Law of Octet In 1869, Mendeleev proposed a periodic table based on atomic mass In 1913, Atomic number was discovered by Mosley.

Octave law of Newland

If elements are organized following a sequence of lower to higher atomic mass, there is evident similarity in physical and chemical properties of each eighth element, which is known as 'Law of Octave'.

Write down the Triads Law.

Chemically similar every three elements have atomic mass such that the middle one has the atomic mass of about the average of the other two- this is the Triads Law.

About Me

Md. Saifur Rahman

B.Sc (Honors), M.Sc (Chemistry)

Former Principal of South Point School and College, Dinajpur.

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