Question

Fill in the blanks-
Periods are___$\left[ {5,6,7} \right]$ horizontal rows of elements in the periodic table and an element with three electrons and two electrons in its valence shell belongs to period____$\left[ {6,3,1} \right]$ and group___ $\left[ {3,6,2} \right]$

Answer 1

Hint: Henry Moseley gave a long form of periodic table in which the elements are arranged in order of their increasing atomic number and after a regular interval elements with similar properties are repeated. The horizontal rows in the periodic table are called Periods and the vertical columns in the periodic table are called Groups.

Complete step by step answer:
-The elements having similar properties in the long form of periodic table are placed in the same period or same group. Due to recurrence of similar valence shell electronic configurations, there is periodic repetition of the properties of elements after certain intervals.
-Periods-There are total seven periods numbered as $1,2,3,4,5,6$ and $7$.The properties of periods in the periodic table-
-The series of elements in each period have the same valence shell.
-The elements of each period have a particular principal quantum number of the valence shell present in them.
-Then according to this the element having three electrons in its valence shell will be placed in the ${\text{3rd}}$ period.
-Groups-There are a total eighteen groups numbered as - $1,2,3,...,16,17,18$. The properties of groups-
-The series of elements in each group have similar valence shells and electrons in the valence shell.
-An element with three electrons and two electrons in its valence shell will be placed in the $2nd$ group.

Periods are_$7$ __ horizontal rows of elements in the periodic table and an element with three electrons in its valence shell belong to period__$3$ __ and group_$2$ __.

Note:
Magnesium is the element which is placed in the third period and second group. Its atomic number is $12$ . It is an alkaline earth metal. Its uses are-
1.It is very light so it is used as the lightest constructional metal in industry.
2.It is used in automobile engines, balances and aircraft construction as an alloy.
3.It is used in flash powders and bulbs.
4.It is used as a deoxidizer for removing the last traces of oxygen from copper and steel.