Not all the elements were included
Dmitri Mendeleev was a Russian chemist; he proposed the modern Periodic Table of elements in 1869.
Many more elements are known today then when Mendeleev laid out his table. In addition, he arranged his table by atomic mass and there are places in the periodic table where mass does not always increase. An example is between tellurium and iodine.
modern periodic law
The properties of elements are the periodic function of their atomic numbers. REMOVAL OF DEFECTS OF MENDELEEV'S PERIODIC TABLE periodic table obtained on the basis of increasing atomic numbers has removed defects of Mendeleev's periodic table . 1) POSITION OF ISOTOPES : since the isotopes of the same elements have the same atomic number, they are given the same place in the table. 2) POSITION OF RARE EARTHS: These elements are separately placed at the bottom of table . similarly Acton elements ( which were discovered after Mendeleev ) are also placed at the bottom of the periodic table. 3) ANOMALOUS PAIRS. the arrangement according to the atomic number show that their placements are correct.
Modern periodic table is based on modern periodic law which states that physical and chemical properties of elemnts are periodic function of their atomic numbers.
1.) The atomic mass in Mendeleev's periodic table does not increase regularly. therefore, it was impossible to predict the number of elements between two elements.The Modern periodic table has been made according to the increasing atomic number (Modern Periodic Law states that 'The properties of an element are the periodic function of its atomic number). The atomic number gives us the number of protons in the nucleus of an atom. the atomic number increases by one as we go from one element to the next. thus, this makes it easy to ascertain how many undiscovered elements may be there between two known elements.2.) Mendeleev's periodic table was made according to increasing atomic masses. we know that of an element have same chemical properties and atomic number, but different atomic masses. So, the concept of isotopes can not be satisfied.The Modern periodic table is according to increasing atomic numbers. Therefore, the problem of isotopes is easily dealt with.
There are 7 periods in the modern periodic table.
The modern periodic table has seven periods.
Modern periodic table is invented by Henry Moseley.
1.) The Atomic Mass in Mendeleev's Periodic Table does not increase regularly. therefore, it was impossible to predict the number of elements between two elements.The Modern periodic table has been made according to the increasing atomic number (Modern Periodic Law states that 'The properties of an element are the periodic function of its atomic number). The atomic number gives us the number of protons in the nucleus of an atom. the atomic number increases by one as we go from one element to the next. thus, this makes it easy to ascertain how many undiscovered elements may be there between two known elements.2.) Mendeleev's periodic table was made according to increasing atomic masses. we know that of an element have same chemical properties and atomic number, but different atomic masses. So, the concept of isotopes can not be satisfied.The Modern periodic table is according to increasing atomic numbers. Therefore, the problem of isotopes is easily dealt with.
Dmitri Mendeleev developed the modern periodic table in 1869.
The modern long form of periodic table was constructed by Neils Bohr based on modern periodic law proposed by Moseley.