Friday 24 July 2020
Thursday 23 July 2020
Periodic table
Periodic classification of elements
Introduction
An orderly arrangement of element is called classification of elements.
Dobereiner's Trials:
Dobereiner arranged the elements in a group of 3 in such a way that the atomic mass of the middle element was nearly the Arithmetic mean of the first and third element for example
The elements Lithium,Sodium and potassium form a triad they are called alkali metals.
Element Li Na K
Active mass 7 23 39
Limitation of Dobereiner classification:
The major draw back of this classification was that all known element could not be arranged in such trieds Dobereiner could identify only 3 trieds from the known element at that time. Hence this system of classification into tried was not successful.
Newland's Law of Octaves:
According this if elements are arranged in order of their increasing atomic masses, the properties of every 8th element are similar of those of first element.
H Li Be B C N O
F Na Mg Al Si P S
Cl K.......
Drawbacks of newland classification of elements
1 this classification is not based on any scientific philosophy.
2 newlands law of octaves is applicable only up to calcium after calcium every element does not possess properties similar to that of the first element.
3 Buland agent that only 56 elements excited in nature and no more element would be discovered in future but now a number of new elements have been discovered which properties do not fit into newlands law of octaves.
4 newlands law of octaves is applicable to lighter elements only.
Mendeleev's Periodic table
Periodic table may be defined as a chat with classify the elements in such a way that elements having similar properties are grouped together in the same vertical column and dissimilar elements are separated a Periodic Table consists of period and Groups
Period: the horizontal rows are called periods.
Group: the vertical column are called groups.
Mendeleev's Periodic Law: the physical and chemical properties of the elements are periodic function of their atomic masses.
Achievements of Mendeleev's Periodic Table
1 mandlif periodic table made the study of elements and their compounds easy
Discovery of new elements and study of their properties
. When all the inert gases are discovered they were placed in a separate group called group without disturbing the original Mendeleev periodic table Mendeleev periodic table could accommodate noble gas when they were discovered noble gases are present only in dresses in atmosphere and are unreactive this is reason that noble gases were discovered to late.
Limitations of defects of Mendeleev classification
Position of hydrogen hydrogen resembles with alkali metals of group 1 and halogen of group 7 there for hydrogen may be placed in group 1 as well as in group 7 does the position of hydrogen is not certain
Position of isotopes atoms of same element having different atomic masses are called isotopes isotopes have same chemical property but different physical properties since in Mendeleev periodic table elements have been arranged in decreasing order of the atomic masses of elements therefore isotopes should be placed in different groups but in Mendeleev periodic table isotopes of an element have been placed together in the same group there was two isotopes of chlorine 35 and chlorine 37 having atomic mass 35 and 37 respectively the blessing of these isotope having different atomic masses together in the same group cannot be justified
Wrong order of atomic mass there are example in Mendeleev periodic table where element of atomic mass have been placed before the element of lower atomic mass for example Cobalt having atomic mass 58.9 comes before having atomic mass 58.7 similarly atomic mass 127.26 can't be for iodine atomic mass 120 6.9 Mendeleev periodic law could not act plan the wrong order of atomic masses
Modern Periodic table or long form of periodic table
Henry moseley observed that atomic number is the fundamental property of elements atomic mass is not the fundamental property of the element there for different elements have different atomic numbers no two different elements can have same atomic number.
In Modern Periodic Table elements are arranged in the order of their increasing atomic number so the periodic law has been modified
Modern Period Law: properties of element are the periodic function of their atomic number when elements are arranged in increasing order of their atomic number the element get arranged according to their electronic configuration secondly when element are arranged in increasing order of their atomic numbers then elements having similar chemical properties and similar electronic configuration or repeated after a regular interval
Repeat Apple of similar properties and similar electronic configuration is called preorder city in properties as well as in electronic configuration of elements having similar electronic configuration have similar chemical properties.
Introduction
An orderly arrangement of element is called classification of elements.
Dobereiner's Trials:
Dobereiner arranged the elements in a group of 3 in such a way that the atomic mass of the middle element was nearly the Arithmetic mean of the first and third element for example
The elements Lithium,Sodium and potassium form a triad they are called alkali metals.
Element Li Na K
Active mass 7 23 39
Limitation of Dobereiner classification:
The major draw back of this classification was that all known element could not be arranged in such trieds Dobereiner could identify only 3 trieds from the known element at that time. Hence this system of classification into tried was not successful.
Newland's Law of Octaves:
According this if elements are arranged in order of their increasing atomic masses, the properties of every 8th element are similar of those of first element.
H Li Be B C N O
F Na Mg Al Si P S
Cl K.......
Drawbacks of newland classification of elements
1 this classification is not based on any scientific philosophy.
2 newlands law of octaves is applicable only up to calcium after calcium every element does not possess properties similar to that of the first element.
3 Buland agent that only 56 elements excited in nature and no more element would be discovered in future but now a number of new elements have been discovered which properties do not fit into newlands law of octaves.
4 newlands law of octaves is applicable to lighter elements only.
Mendeleev's Periodic table
Periodic table may be defined as a chat with classify the elements in such a way that elements having similar properties are grouped together in the same vertical column and dissimilar elements are separated a Periodic Table consists of period and Groups
Period: the horizontal rows are called periods.
Group: the vertical column are called groups.
Mendeleev's Periodic Law: the physical and chemical properties of the elements are periodic function of their atomic masses.
Achievements of Mendeleev's Periodic Table
1 mandlif periodic table made the study of elements and their compounds easy
Discovery of new elements and study of their properties
. When all the inert gases are discovered they were placed in a separate group called group without disturbing the original Mendeleev periodic table Mendeleev periodic table could accommodate noble gas when they were discovered noble gases are present only in dresses in atmosphere and are unreactive this is reason that noble gases were discovered to late.
Limitations of defects of Mendeleev classification
Position of hydrogen hydrogen resembles with alkali metals of group 1 and halogen of group 7 there for hydrogen may be placed in group 1 as well as in group 7 does the position of hydrogen is not certain
Position of isotopes atoms of same element having different atomic masses are called isotopes isotopes have same chemical property but different physical properties since in Mendeleev periodic table elements have been arranged in decreasing order of the atomic masses of elements therefore isotopes should be placed in different groups but in Mendeleev periodic table isotopes of an element have been placed together in the same group there was two isotopes of chlorine 35 and chlorine 37 having atomic mass 35 and 37 respectively the blessing of these isotope having different atomic masses together in the same group cannot be justified
Wrong order of atomic mass there are example in Mendeleev periodic table where element of atomic mass have been placed before the element of lower atomic mass for example Cobalt having atomic mass 58.9 comes before having atomic mass 58.7 similarly atomic mass 127.26 can't be for iodine atomic mass 120 6.9 Mendeleev periodic law could not act plan the wrong order of atomic masses
Modern Periodic table or long form of periodic table
Henry moseley observed that atomic number is the fundamental property of elements atomic mass is not the fundamental property of the element there for different elements have different atomic numbers no two different elements can have same atomic number.
In Modern Periodic Table elements are arranged in the order of their increasing atomic number so the periodic law has been modified
Modern Period Law: properties of element are the periodic function of their atomic number when elements are arranged in increasing order of their atomic number the element get arranged according to their electronic configuration secondly when element are arranged in increasing order of their atomic numbers then elements having similar chemical properties and similar electronic configuration or repeated after a regular interval
Repeat Apple of similar properties and similar electronic configuration is called preorder city in properties as well as in electronic configuration of elements having similar electronic configuration have similar chemical properties.
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