Question

Why is ionization enthalpy of Beryllium higher than Boron.

Answer 1

Beryllium is an element from group 2 and the second period of the periodic table. The atomic number of beryllium is 4. The chemical symbol of this element is Be. On the other hand, boron is an element of group 13 and the second period. The atomic number of this element is 5.

Complete step by step answer:
The ionization energy of an element depends upon many factors. Some important factors are the size of the atom, effective nuclear charge, tendency to form a stable electronic configuration, losing off a stable electronic configuration, etc.
In the case of beryllium, the electronic configuration is $1{s^2}2{s^2}$. This electronic conjugation has a symmetric distribution which makes it stable. Due to this stable electronic configuration, the energy required to remove the electron from its outermost shell is very high.
On the other hand, for boron, the electronic configuration is $1{s^2}2{s^2}2{p^1}$. In this configuration removal of one electron generates a stable symmetric configuration. Therefore, the energy required to remove one electron from a boron requires less energy.
Due to these reasons ionization enthalpy of Beryllium is higher than Boron.

Note: From left to right of a period size decreases as nuclear charge density increases. In this viewpoint ionization enthalpy of Beryllium should be lower than Boron. But in this case, formation of stable symmetric electronic configuration overcomes the effect of size.