Mosely

atomic structure

1. Atomic structure and the modern Periodic table

2. HENRY MOSELY English physicist The studies conducted by Mosley regarding the properties of elements related to their position in the periodic table finally proved that the basic properties of elements depend on their atomic numbers and not on atomic masses .

3. Modern Periodic Table When more and more elements were discovered ,small changes were to be made in Mendeleev ‘s periodic table . In 1914 , Mosley suggested that elements should be arranged in the ascending order of the atomic number .

4. Modern Periodic Law Properties of elements depend on their atomic numbers . When elements are arranged in the ascending order of their atomic numbers there is a repetition of their properties at fixed intervals

5. Peculiarities of modern periodic table There are 7 periods in periodic table There are 18 groups in the periodic table.

6. Representation of each element in modern periodic table Atomic number 3 Symbol Li Name Lithium Atomic mass 6.9 Electronic distribution 2 , 1

7. Peculiarities of periods of periodic table One of the period is given below :- In the period , as the atomic number increases the number of valence electron also increases . After fixed intervals , the distribution of electrons in the outermost shell gets repeated in the same way . Li Be B C N O F Ne

8. Peculiarities of ‘groups ‘ of periodic table The electron distribution of elements in group 1 and group 2 is as given below: - The number of valence electrons of the elements that come in same groups are equal . The elements in the same group shows similar properties since the number of valence electrons are equal and general electron structure are the same . Group 1 Group 2 H 1 Li 2,1 Be 2,2 Na 2,8,1 Mg 2,8,2 K 2,8,8,1 Ca 2,8,8,2

9. Relationship between the group number and the number of valence electrons Group number Name of the element family Number of valence electrons Valency 1 Alkali metal family 1 1 2 Alkaline earth metal family 2 2 13 Boron family 3 3 14 Carbon family 4 4 15 Nitrogen family 5 3 16 Oxygen family 6 2 17 Halogen family 7 1 18 Noble gas family 8

10. There is a relation between group number and valence electrons . In group 1 and group 2 ,number of valence electrons is equal to the group number . Elements 13 and 18 , 10 is added to valence electron to get the group number . By knowing the number of valence electrons we can find the group number and valency . Valency is the number of electrons released or accepted by the atom of an element to complete its octet .

11. The elements in group 3 to 12 are called transition elements . The position of transition elements is in between the metals and non – metals . They are so called because they indicate a gradual progressive change from metallic to non – metallic properties .

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