what is the number of elements in 1st 2nd 3rd period of periodic table give reason for your answer
Answers
1st period will have only 2 elements and is called short period(hydrogen, helium).
2nd and 3rd period will have 8 elements.
We can explain the number of elements in these periods based on how electrons are filled into various shells. The maximum number of electrons that can be accommodated in a shell depends on the formula 2n square where n is the number of shells.
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Answer:
The first period contains 2 elements and is called a very short period. The second and third periods contain 8 elements each and are called short periods.
Explanation:
All the elements in the periodic table are arranged in the order of their increasing atomic number.
The first period begins with the filling of the first energy shell (K-shell). The first energy shell can accommodate only 2 electrons in it. Hence, there are only 2 elements in the first period.
The second period begins with the filling of the second energy shell (L-shell). The second energy shell can accommodate only 8 electrons in it. Hence, there are only 8 elements in the second period.
After the addition of 8 electrons to the second shell, the second shell becomes completely filled. Now, the next electron enters the third shell and the elements now go to the third period. The third shell has the capacity to accommodate 18 electrons. However, after the third shell receives 8 electrons, the filling of the fourth shell begins. This is because the outermost shell does not have the capacity to hold more than 8 electrons. Therefore, the third period has only 8 elements.
I hope it helped you...