   Chapter 7, Problem 78SCQ

Chapter
Section
Textbook Problem

Explain why the first ionization energy of Ca is greater than that of K, whereas the second ionization energy of Ca is lower than the second ionization energy of K.

Interpretation Introduction

Interpretation:

The first ionization energy of Calcium is greater than Potassium and the second ionization energy of Calcium is lower than Potassium; the reason has to be predicted.

Concept Introduction:

Ionization energy (IE): The ionization energy is the required to remove an electron from an atom in the gas phase.

General formula of ionization energy= Atom in the ground state(g)Atom+(g)+eΔU=Ionizationenergy(IE)

As predicted by coulomb’s law, energy must be supplied to overcome the attraction between an electron and the nucleus and to separate the electron from the atom. Thus ionization energies always have positive values. An electron father from the nucleus generally has smaller ionization energy and electron closer to the nucleus has larger ionization energy.

Increase and decrease electro negativity: The less vacancy electrons an atoms has the least it will gain of electrons. Moreover the electron affinity decrease down the groups and from right to left across the periods on the periodic table, the reason is electrons are placed in a higher energy level far from the nucleus thus a decrease from its pull.

Explanation
• Let analyze the first ionization energy of calcium (Ca) and potassium (K) atoms:

First ionization energy of Calcium (Ca), IE1= 579 kJ/mol

Commonelecronicconfigurationof Calcium(Ca)[1s22s22p63s23p64s2][1s22s22p63s23p64s1]+e-[lossofoneelectrons]

First ionization energy of Potassium (K), IE1= 419 kJ/mol

Commonelecronicconfigurationof potassium (K)[1s22s22p63s23p64s1][1s22s22p63s23p64s0]+1e-[lossofoneelectrons]

The removal of one electron from Potassium is easy because it attains noble gas configuration. But removal of electron from the completely filled s-orbital needs little more energy than Potassium.

• Let us consider the Second ionization energy of Calcium (Ca) and Potassium (K) atoms

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