About 200 years ago, we knew about very few elements. Due to which we did not have any difficulty in studying their properties separately, but over time, one by one many Periodic table of elements Invented. to study their properties separately scientists began to feel difficulty.
To avoid this dilemma, scientists conceived the periodic table “in which elements with similar properties are in a group so that by studying the properties of an element of a particular group, the properties of other elements in that group can be predicted.” ,
History of periodic table – History of periodic table
First in the 18th century Lavoisier The scientist of the name divided the element on the basis of metal and non-metal, according to them some properties are found equally in all metals.
In 1866, the British scientist John Newlands described the elements discovered till his time. atomic mass By decorating in sequence, a rule was propounded, which is called Newland’s octet law.
Newland’s law of octetAccording to this rule, if the elements are arranged in the order of their increasing atomic masses, then starting from any element, the properties of the eighth elements are the same as the properties of the first element. As- The eighth note of the music is the same as the first vowel.
Inspired by Newland’s octet law, in 1869 the Russian chemist Dmitry Mendeleev developed a new system of classification of elements by studying the physical and chemical properties of elements in depth. In this system, he saw the elements arranged in the order of increasing atomic masses.
And on the basis of his findings, Medlive formulated a law which is also called Medlive’s periodic law.
Medlive’s periodic lawAccording to this law “the physical and chemical properties of elements are the periodic function of their atomic masses.” In other words, if the elements are arranged in the order of their increasing atomic number, then after a certain number of elements similar properties are found.
At the beginning of the 19th century, the German chemist John Doebrenner chemically divided the elements into three groups. What we know today as the Trinity Law.
trinity law According to this rule, when the elements of the triad are arranged in their atomic order, the atomic number of the middle element is the average of the atomic numbers of the remaining two elements on the side.
Mendeleev’s periodic table
At the time of Mendeleev only 63 elements were known. In 1871, on the basis of his law, Mendeleev created a table of elements called Mendeleev’s periodic table it is said.
Features of Mendeleev’s periodic table – Some interesting features about Mendeleev periodic table in hindi
1) Columns in this periodic table are called squares which are represented by Roman numerals. Each group is divided into two groups A and B.
2) The horizontal rows of this table are called periods.
Usefulness of Mendeleev’s periodic table
1) With the help of this table it has become very easy to study the elements and their properties. Once the information about one element of a class is known, complete inference can be made about all the elements of that class.
2) Mendeleev, while preparing his table, had left some blanks in the table for some unknown elements. He had clearly said that later on when these elements are invented, they will be kept in these vacant places.
3) At the time of Medlive, the atomic masses of some elements were incorrectly worked out. Which Medlive corrected with his periodic table.
Atomic mass = equivalent mass × valence,
4) Placed in Mendeleev’s periodic table. Elements of a particular group have the same valency.
Mendeleev periodic table defects
1) The position of hydrogen in this periodic table is not correct.
2) There are two categories of soil elements called lanthanides and actinides. These are placed in 2 separate rows from the periodic table.
3) In Mendeleev’s periodic table, the elements are arranged in the order of their increasing mass, but some elements do not follow this rule. For example, cobalt and nickel.
4) There is no fixed position for isotopes in Medlife’s periodic table.
Invention of Modern Periodic Table – Discovery of modern periodic table
In 1913, Moseley reported that cathode rays striking an element produce a new type of rays called X-rays.
The element on which cathode rays strike is called anticathode. Moseley, using several elements as anticathodes, found that according to the nature of the elements, X number of different frequencies are born. In this experiment, Moseley found that the atomic number, not the atomic mass, is the most possessive property of the element.
According to Moseley, “The physical and chemical properties of elements are a periodic function of their atomic numbers”.
The modern periodic table is presented by arranging the elements on the basis of atomic number.
Properties of modern periodic table
1) In the modern periodic table, the elements are arranged in the order of their increasing atomic number.
2) Modern periodic table has 18 columns except lanthanides and actinides.
3) Lanthanide and Actinide are in two rows at the bottom of this periodic table.
4) The modern periodic table is divided into 4 blocks. These are four blocks – s, p, d and f.
Features of the Modern Periodic Table
-Characteristics of periodic table in hindi
1) Elements of class 1 of the modern periodic table have similar properties due to their similar external electronic configuration.
2) There is a gradual change in the properties of elements from top to bottom in a group because the attraction between the nucleus of the atom and its outer valence electron changes.
1) electronic configuration–
All the elements of a group have the same bar electronic configuration. Meaning all the elements have the same number of valence electrons in the atom.
Which group of elements in the modern periodic table have the same valency?
3) ionization energy–
The energy required to detach an electron bound by the weakest force in a gaseous atom is called ionization energy.
Defects of modern periodic table in hindi
The modern periodic table has removed most of the shortcomings of Medleyev’s periodic table. However, it has the following drawbacks.
1) The position of hydrogen in the modern periodic table is not as accurately determined as in Medliff’s periodic table.
2) According to the electronic configuration, helium should have been in group 2 with alkaline earth metals. But it is placed in group 18 along with inert gases.
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