Question

Electronic configuration of an atom is 2,8,7. To which of the following elements would it be chemically similar?
[A] Nitrogen (Z = 7)
[B] Fluorine (Z = 9)
[C] Phosphorous (Z = 15)
[D] Argon (Z = 18)

Answer 1

Hint: To find the correct answer, write down the electronic configuration of the given elements. The atomic number is also given so use that to find out the electronic configuration. The element which will have the same number of electrons outer shell will behave similarly.

Complete answer:
The electronic configuration of an element is given to us as 2, 8, 7 which means it has 7 electrons in its outermost shell. Let us discuss about its possible chemical properties.
As we can see it has 7 electrons therefore it will readily accept one more electron in order to gain a stable noble gas configuration. Among the given options, the one will 7 electrons in its valence shell will also behave similarly i.e. it will also accept an electron to achieve a stable noble gas configuration.
Let us write down the electronic configuration of the given elements to figure out which one will behave similarly.
Firstly, we have nitrogen. Its atomic number is given to us which is 7. Therefore, its electronic configuration will be 2, 5. It will not behave chemically similar to the element with configuration 2, 8, 7. Therefore, this is not the correct answer.
Next, we have fluorine whose atomic number is 9. Therefore, its electronic configuration will be 2,7. As we can see it has 7 electrons in its valence shell i.e. it will also act as an oxidising agent and accept one electron to gain stability thus, react similarly to the element with configuration 2, 8, 7. Therefore, this is the correct answer.
Next, we have phosphorus and its atomic number is 15. Therefore, its electronic configuration will be 2, 8, 5. It is not chemically similar therefore, this is also incorrect.
Lastly, we have argon. Its atomic number is given to us which is 18. Therefore, its electronic configuration is 2, 8, 8. Its octet is already filled thus it will not react readily and this is not the correct answer either.
As we can see from the above discussion that fluorine will have similar chemical behaviour as the given element.

Therefore, the correct answer is [B] Fluorine (Z = 9)

Note:
The element given to us here is chlorine and its atomic number is 17. Both chlorine and fluorine are in the same group in the periodic table, group 17. Group 17 elements are called halogens. Halogens are strong oxidising elements and they are highly electronegative. Fluorine is the most electronegative element and in free-state, it exists as fluoride ion.