How Many Elements Did Mendeleev's Periodic Table Contain

Introduction

There are 118 elements in Mendeleev’s Periodic Table. In Science, we have three main subjects that are Chemistry, Physics, and Biology. Chemistry deals with the structure of matter and energy and the way they interact with each other. The atoms are considered the basic building blocks of matter and the whole chemistry revolves around these atoms and molecules. Physics deals with the natural phenomena occurring on the earth whereas Biology deals with the study of all living organisms like plants and animals. In chemistry, we have elements like Hydrogen(H), Lithium(Li), Argon(Ar) etc which are written down in the Periodic Table. So Let’s learn more about these Periodic Tables.

Periodic Table

It is a two-dimensional structured table which consists of a list of chemical elements discovered on the earth. It is arranged in the increasing order of their atomic number.

The periodic Table is generally considered an icon of chemistry. The tackle is roughly divided into four rectangular areas called blocks. Rows of the periodic table are called periods and columns of the periodic table are called Groups.

There are two periodic tables:

• Mendeleev's Periodic Table

• Modern Periodic Table

Periodic Law

According to the periodic law, Elements in the column have similar properties. In the periodic table elements at the left are generally metals and elements at the right are non-metals. The chemical properties of different elements are determined by their atomic number. The atomic Number is the total number of protons present in the nucleus of the atom. The Atomic Number of an element is represented by the letter ‘Z’. The number of electrons present in a neutral atom is always equal to the number of protons present in the nucleus of the atom.

Mendeleev’s Periodic Table

It is the first periodic table invented by Russian chemist Dmitri Ivanovich Mendeleev in 1869 and was generally accepted. Mendeleev invented this table after the rejection of Newland’s Octave Law. At the time of Mendeleev, there were 63 elements known. So Mendeleev arranged these elements horizontally in 10 series in the order of their increasing atomic weights. There were 7 horizontal columns known as periods and 8 vertical columns known as groups.

Mendeleev Periodic Law

Mendeleev is known as the father of the Periodic Table as he is the first person to arrange all the elements known at that time in the form of a table called Mendeleev’s Periodic Table.

He arranged all the elements according to the elements atomic weight. He developed a law called Mendeleev’s Periodic Law. According to Mendeleev’s periodic law, “The physical and chemical properties of the elements are the periodic function of their atomic weights”.

From his law, two points (inferences) can be drawn:

• The Physical and Chemical Properties of elements can be determined by their atomic masses(weights).

• Elements which have similar physical and chemical properties can be arranged together in the increasing order of their atomic masses.

Characteristics of Mendeleev’s Periodic Table

• Mendeleev’s Periodic table consists of 9 groups which are indicated by roman numbers such as I, II, III, IV, V, VI, VII, VIII, and zero.

• There are 7 periods in the table and also to accommodate more elements periods 4, 5, 6, and 7 are divided into two halves.

• The first period consists of only two elements and is called the shortest period. The second and 3rd periods consist of 8 elements each known as a short period.

• Periods 4th and 5th have 8 elements each and are considered as long periods.

• The 6th period with 32 elements is considered the longest period.

• The last period, i.e., The 7th period is incomplete since the elements are being added in this period.

Certain Problems Related to Mendeleev's Periodic Table

Q1. How do the atomic masses of certain elements are corrected?

Ans: Mendeleev's periodic table was useful for the correction of atomic masses of certain elements. For example, the atomic mass of Beryllium is used as 14.8 but it was corrected by Mendeleev as 9 based on the position of Beryllium.

Q2. List one defect in Mendeleev’s Periodic Table.

Ans: Hydrogen should be placed in both groups IA and VIIA since it exhibits both the properties of alkali metals and halogens. But hydrogen has been placed in IA(alkali metals) group.

Q3. What do you mean by anomalous pairs of elements?

Ans: Elements which are not placed correctly in the periodic table that is not according to increasing atomic weights are called anomalous pair of elements.

Q4. Give any one anomalous pair of elements.

Ans: Argon and Pottasium, Argon has more atomic weight than Potassium but it is placed before Potassium.

Q5. Which periodic table overcome defects in Mendeleev’s periodic table?

Ans: The Modern Periodic table overcame the defects in Mendeleev’s periodic table.

Conclusion

• Mendeleev invented the first periodic table in 1869.

• He arranged the elements in the increasing order of their atomic masses.

• 63 Elements were known at the time of Mendeleev.

• It states that elements are the periodic function of their atomic masses.

• A periodic table is a 2-D structure consisting of all the chemical elements. The elements are arranged in the increasing order of their atomic number in the periodic table.