Noble gases have______________ electron affinity A.High B.Low C.Zero D.Very low
Hint: Electron affinity is defined as the energy change when an electron is added to the outermost shell of an isolated gaseous atom. Electron affinity is usually negative. Electron affinity generally becomes more negative with an increase in atomic number across a period. The effective nuclear charge increases across a period and it is easier to add electrons when there is less charge so it becomes more negative across the period. It becomes less negative down the group as nuclear charge decreases Noble gases have completely filled outer electrons and have stable configuration. They do not take part in bonding. So, they have no electron affinity.
Complete answer: A.High: High electron affinity is possessed by elements that have a low size and high nuclear charges like chlorine hence this option is not correct. B.Low: low electron affinity is possessed by elements that have large size and low nuclear charge like sodium. Hence this option is also not correct. C.Zero: Electron affinity is zero for those elements which have fully filled electron configuration like noble gases. Hence this option is correct. D.Very low: The electron affinity is very low for an element having very low nuclear charges for example strontium. Hence this option is not correct.
So our required Ans is C that is Zero.
Note: Electron affinity of oxygen and fluorine is less negative as compared to succeeding elements because when electrons are added the electron goes to n=2 quantum number and suffers significant repulsion from other elements present in this level. For n=3 e.g. Cl, the added electron occupies a larger region of space, and electron repulsion is much less.