Question

The element having highest electron affinity is:
A) Fluorine
B) Nitrogen
C) Chlorine
D) Oxygen

Answer 1

Hint: The answer to this question is based on the definition of electron affinity definition which is nothing but the energy required to add an electron to the outermost orbital of an atom and this fact can help you to deduce the correct answer.

Complete answer:
In the classes of inorganic chemistry, we have studied the periodic table and the properties of elements in the group as well as periods and also we are familiar about the trends in the physical and chemical properties across groups and periods.
Let us now see what does electron affinity means and how can we find the element which is having the highest electron affinity among the given data.
- Now, according to the definition of electron affinity, when we add an electron to the outermost orbit of an atom then the atom possesses a negative charge and also the enthalpy of that reaction is a negative value.
- Now, consider the atoms given in the question that are fluorine, nitrogen, oxygen and chlorine.
Among these elements the first three elements are belonging to the period number 2 and chlorine is placed below fluorine and when we move from left to right across the period, the effective nuclear charge increases and in turn increases and in above said fact, the fluorine has greater electron affinity.
- But since fluorine and chlorine are placed in the same group, on going down the group the effective nuclear charge decreases and also electron affinity decreases. But here, because of the small size of the atoms of period 2 than period 3 elements, the electron pair repulsion is high in fluorine and addition of electrons goes unfavourable.
- Therefore, electrons can be easily added to chlorine due to less electronic repulsions between them and thus have the highest electron affinity.

Therefore, the correct answer is option C) Chlorine.

Note: To understand the trends in the periodic table, you must be thorough with periodic table and also do not be confused about the electron affinity and ionisation energy because electron affinity is the energy required to add an electron to the outermost orbit of atom and ionisation energy is the energy required to remove an electron from outermost orbit of an atom.