Which of the following atoms has the
highest first ionization energy ?
(1) Rb
(2) Na
(3) K
(4) Sc
Answers
(4) ScDue to poor shielding of d-electrons in Sc, Zeff of Sc becomes more so that ionisation energy of Sc is more than Na, K and Rb.
Answer: Option (2) is the correct answer.
Explanation:
When an electron is removed from a gaseous atom or ion then the energy required to remove the electron is known as ionization energy.
When one electron is removed from valence shall then it is known as first ionization energy. When second electron is removed then it is known as second ionization energy.
Ionization energy decreases down the group because number of shells increases so does distance between the nucleus and valence shell. Hence, less energy is needed to remove an electron.
Therefore, sodium (Na) will have the highest ionization energy because it has the smallest size out of the given options. So, energy required to remove the electron will be highest due to smallest distance between nucleus and valence shell.
Therefore, we can conclude that Na atom has the highest first ionization energy.