Mendeleev Periodic Table

Mendeleev’s Periodic Table was the first bold attempt to arrange all the known elements in a proper manner. This table was based on the principle of Mendeleev’s Periodic Law and was a significant step made in the direction of arranging all the known elements. 

According to Mendeleev, the characteristics of elements are a periodic function of their atomic masses and thus he arranged all the known elements of that time in increasing order of their atomic mass in the form of a table called Mendeleev’s Periodic Table.

Let’s learn more about Mendeleev’s Periodic Law and his periodic table in detail in this article.

What is Mendeleev’s Periodic Law?

People from the very start tried to arrange known elements in a proper manner to study their properties in a more effective manner. Various people have come up with various ideas to arrange the elements such as the New Land law of Octaves, Dobereiners Triads, etc. But the most significant step in this direction was made by the famous Russian scientist Dmitri I. Mendeleev in 1869. He based his theory on the basis that the properties of chemical elements are the function of their atomic mass. According to him, ” The physical and chemical properties of the elements are the periodic function of their atomic weights.” This law is called Mendeleev’s Periodic Law.

Who is called the Father of Periodic Table?

The famous Russian scientist Dmitri Ivanovich Mendeleev also called Mendeleev is called the Father of the Periodic Table. He was born on 8 February 1834 in the small town of Tobolsk in Siberia. He was an alumnus University of St. Petersburg. and received and received his Master’s degree in chemistry in 1856 and his doctoral degree in 1865.

Introduction to Mendeleev Periodic Table

In 1869, Dmitri Mendeleev came up with a periodic table of chemical elements based on the properties that appeared in the elements. He placed the elements from lightest to heaviest. Before Mendeleev’s Periodic Table, Dobereiner’s triads and Newland’s Law of Octaves were mostly considered for the classification of elements in the form of tables. 

Mendeleev’s Periodic Table came into the picture after the rejection of Newland’s Law of Octaves. In Mendeleev’s Periodic Table, elements are distributed according to their atomic masses, fundamental property, and chemical properties. 

Mendeleev’s Periodic Law states that “The properties of elements are the periodic function of their atomic masses.”

At the time when Mendeleev formulated this periodic table, only 63 chemical elements had been discovered. After observing all the properties of the elements, Mendeleev concluded that the properties of the elements periodically related to their atomic masses. Other than atomic masses, Mendeleev also used chemical properties to categorize. Formulae of hydrides and oxides of the elements were one of the primary criteria for categorization. He arranged the elements in the periodic table such that all the elements with similar properties would fall in the same vertical columns of the periodic table. He named the vertical columns “groups” and the horizontal rows “periods“.

Group		I	II	III	IV	V	VI	VII	VIII
Oxide		R2O	RO	R2O3	RO2	R2O5	RO3	R2O7	RO4
Hydride		RH	RH2	RH3	RH4	RH3	RH2	RH
Periods ⇓		A      B	A       B	A       B	A       B	A       B	A       B	A       B	Transition Series
1		H 1.008
2		Li 6.939	Be 9.012	B 10.81	C 12.011	N 14.007	O 15.999	F 18.998
3		Na 22.99	Mg 24.31	Al 29.98	Si 28.09	P 30.974	S 32.06	Cl 35.453
4	First series:	K 39.102	Ca 40.08	Sc 44.96	Ti 47.9	V 50.94	Cr 50.2	Mn 54.94	Fe 55.85	Co 58.93	Ni 58.71
	Second series:	Cu 63.54	Zn 65.37	Ga 69.72	Ge 72.59	As 74.92	Se 78.96	Br 79.909
5	First series:	Rb 85.47	Sr 87.62	Y 88.91	Zr 91.22	Nb 92.91	Mo 95.94	Tc 99	Ru 101.07	Rh 102.91	Pd 106.4
	Second series:	Ag 107.87	Cd 112.4	In 114.82	Sn 118.69	Sb 121.75	Te 127.6	I 126.9
6	First series:	Ce 132.9	Ba 137.34	La 138.91	Hf 178.49	Ta 180.95	W 183.85		Os 190.2	Ir 192.2	Pt 195.09
	Second Series:	Au 196.97	Hg 200.59	Ti 204.37	Pb 207.19	Bi 208.98

Mendeleev recognized the significance of periodicity. He used a broader range of physical and chemical properties in order to classify the chemical elements. Particularly, he relied on the similarities in the given empirical formulas and properties of the compounds such as oxides and hydrides formed by the elements.

Mendeleev noticed that some of the elements didn’t fit according to the periodic law if the order of atomic masses was followed strictly. He thus ignored the order of atomic masses, assuming that the atomic measurements might be incorrect, and placed the elements with similar properties together. For example, the atomic mass of Tellurium is more than that of Iodine. Yet, he placed Iodine with Group VII and Tellurium in Group VI. This was because Iodine has more similar properties to Chlorine, Fluorine, and Bromine. At the same time, keeping his primary aim of arranging the elements of similar properties in the same group, he proposed that some of the elements were still undiscovered and, therefore, left several gaps in the table. 

Merits of Mendeleev’s Periodic Table

Merits of Mendeleev’s Periodic Table are,

• It was one of the first periodic tables that successfully accommodated all known elements at that time.
• It gave the periodic law based on which the modern periodic law was formed.
• The table had gaps for undiscovered elements, which proved to be beneficial in the discovery of new elements. The periodic table was not disturbed in any way.
• Mendeleev’s Periodic Table in 1869 had only seven groups, but Sir William Ramsay suspected new elements belonging to a hitherto unknown eighth group.
• Ramsey and Rayleigh discovered noble gases in 1895. These noble gases were added to Mendeleev’s Periodic Table as a separate group.

Demerits of Mendeleev’s Periodic Table

Demerits of Mendeleev’s Periodic Table are,

• Hydrogen, the first element to begin with didn’t have a definitive place on the table. It was placed differently from the rest of the elements.
• Isotopes are variants of a particular element that have the same atomic number but differ in atomic mass. These isotopes violated Mendeleev’s Periodic Table as they couldn’t be placed.
• The increase in the atomic mass of the elements is irregular and not in a fixed pattern. Thus, it was not possible to exactly determine how many elements were yet to be discovered.

Predictions of Mendeleev’s Periodic Table

Mendeleev has made various predictions on the elements that are not known till that time on the basis of the atomic mass of the other elements present. 

• Mendeleev predicted several elements after observing his periodic table. He estimated that some unfilled spots would be similar to elements existing in the given group.
• He named some elements as (eka)-(similar element), where Eka means ‘one’ in Sanskrit.
• Mendeleev predicted eka-boron (Eb), eka-aluminium (Ea), eka-manganese (Em), and eka-silicon (Es).
• These elements were later discovered to be Scandium, Gallium, Technetium, and Germanium respectively.
• Mendeleev also predicted an element between Thorium and Uranium amongst others.

Mendeleev’s Predictions and Actual Properties on Discovery:

Property	Eka-silicon (predicted)	Germanium (found)	Eka-aluminium (predicted)	Gallium (found)
Atomic Weight	72	72.6	68	70
Density	5.5	5.36	5.9	5.94
Melting Point	High	1231	Low	302.93
Formula of oxide	EO2	GeO2	E2O3	Ga2O3
Formula of chloride	ECl4	GeCl4	ECl3	GaCl3

To conclude, in his time, Dmitri Mendeleev made a very insightful Periodic Table based on the Atomic Masses of Elements. It was the foundation of the Modern Periodic Table and successfully predicted several unknown elements of that time.

Difference between Mendeleev’s Periodic Table and Modern Periodic Table

The difference between Mendeleev’s Periodic Table and Modern Periodic Table are discussed below in the table,

Mendeleev’s Periodic Table	Modern Periodic Table
This table is based on the atomic masses of the given elements.	This table is based on the atomic number of the given elements.
The chemical elements are arranged in the increasing order of their atomic masses.	The chemical elements are arranged in the increasing order of their atomic numbers.
Hydrogen doesn’t have a fixed place in this table.	Hydrogen has a fixed place in this table.
This table has 7 groups and 6 periods.	This table has 18 groups and 7 periods.
Isotopes violate this table and have no allotted place.	Isotopes are placed in the same element as the atomic number is constant throughout.

Read More,

• Periodic Classification of Elements
• History of Periodic Table
• Merits of the Modern Periodic Table

FAQs on Mendeleev’s Periodic Table

Q1: What is basis of Mendeleev’s Periodic Table?

Answer:

The basis of Mendeleev’s periodic table is the arranging of elements on the basis of their increasing order of their atomic weight. Mendeleev had arranged all the 63 elements known at that time in the form of a table with  7 horizontal columns (period) and 8 vertical columns (groups known as Mendeleev’s periodic table.

Q2: What is the Law of the Mendeleev Periodic Table?

Answer:

Mendeleev gave the famous Mendeleev Periodic law which explains that ” The periodic properties of the elements are the periodic function of their atomic mass.”

Q3: How did Mendeleev calculate the Atomic Masses of the unknown Chemical Elements?

Answer:

Mendeleev did not calculate atomic masses on his own. He used the masses of existing elements to place them in the table and predict the masses of undiscovered elements. Mendeleev predicted eka-boron (Eb), eka-aluminium (Ea), eka-manganese (Em), and eka-silicon (Es), which were later discovered to be scandium, gallium, technetium and germanium respectively.

Q4: Did Mendeleev violate the Periodic Law in the table? Explain.

Answer:

Mendeleev arranged the elements according to the atomic masses. Yet, there were instances where he had to place elements not in sequence to ensure that elements with similar properties were in the same group. Therefore, he had to violate the periodic law and ignore the order of atomic masses in some cases. 

For example, the atomic mass of Tellurium is more than that of Iodine. Yet, he placed Iodine with Group VII and Tellurium in Group VI. This was because Iodine has more similar properties to Chlorine, Fluorine and Bromine.

Q5: Why couldn’t Mendeleev place Hydrogen in the periodic table?

Answer:

Hydrogen reacts with metals to form ionic compounds called hydrides and also with non-metals to form covalent compounds. Mendeleev’s periodic law could not assign a fixed position to hydrogen in the periodic table because hydrogen resembled both alkali metals (Group 1) and halogens (Group 17) in some of its properties. 

Q6: How did isotopes violate Mendeleev’s Periodic Table?

Answer:

Isotopes are variants of a particular element that have the same atomic number but differ in atomic mass. As Mendeleev’s Periodic Table is according to the atomic masses, he couldn’t place one element twice in the table. Thus, isotopes violate the table and can’t be placed. 

Q7: What is the difference between Mendeleev and Modern periodic table?

Answer:

The basic difference between Mendeleev and Modern periodic table is that Mendeleev’s periodic table arranged elements on the basis of their atomic weight whereas Modern periodic table arranged elements on the basis of their atomic number.

Q8: What is Mendeleev famous for?

Answer:

Mendeleev the famous Russian scientist is known for his work in arranging all the known element till that time in the form of a table which make it easier for us to study their properties.