Question

Choose from the following:
$_6$C, $_8$O, $_{10}$Ne, $_{11}$Na, $_{14}$Si
A. Elements that should be in the same period.
B. Elements that should be in the same group.
State reason for your selection in each case.

Answer 1

Hint: We can select on the basis of their atomic numbers by writing the respective electronic configurations. In the modern periodic table positions are assigned according to the atomic numbers, and valence shell of elements.

Complete step by step answer:
First, let us write the electronic configuration of given elements.
Now, the first we have carbon with the atomic number 6, and its electronic configuration is 2, 4. Second is oxygen with atomic number 6, its configuration is 2, 6.
Similarly, we will write for the other elements Ne (10) – 2,8
Na (11) – 2, 8, 1
Si (14) – 2, 8, 4
As we know, the elements having the same period are assigned on the basis of the valence shells, or the no. of shells filled.
Now, for the part (i) we can see C, O, and Ne are filled up in the first two shells, so they will be in the period 2, whereas Na, and Si are filled up in the first three shells, so they will be assigned the period 3.
If we talk about the group, then it is assigned on the basis of valence electrons, it means electrons required to complete the octet.
Let us consider carbon, it has 4 valence electrons, oxygen has 2 electrons, Ne has complete octet, Na has 1 valence electrons, and Si has 4 valence electrons.
Thus, for the part (ii) we can say that C, and Si belongs to the same group i.e. 14.
Neon belongs to the halogen group, whereas sodium to the group I-A, and oxygen to that of chalcogens, i.e. group 16.
In the last, we can conclude that elements belonging to the same period are C, O, and Ne i.e. period 2; and Na, and Si to period 3. The elements C, and Si belongs to the same group i.e. group 14.

Note: Don’t get confused while differentiating between the elements. Just write down their electronic configuration, and separate them according to the rules of assigning the positions in the modern periodic table. If you don’t remember the atomic numbers of the elements, then look at numbers mentioned in the subscripts.