Problem 18 - Chemistry A Guided Inquiry

Question

Within our model and referring to the Coulombic Potential Energy expression, explain why the IE increases from left to right across a row of the periodic table.

Step-by-Step Solution

Answer

Ionization energy increases from left to right across a row of the periodic table because, as the atomic number increases in a period, the nuclear charge also increases and the atomic radius decreases. This stronger attraction between nucleus and electron requires more energy to remove an electron, making the ionization energy higher. This fact is reflected in the Coulombic Potential Energy equation, where a larger charge and a smaller distance lead to higher energy.

Step 1: Understanding atomic structure

In a neutral atom, the number of electrons equal the atomic number. Going from left to right in a period of the periodic table, the atomic number increases, meaning that there are more electrons and protons in an atom. More protons mean a stronger nuclear charge, attracting the layer of electrons more strongly thereby reducing the atomic radius.

Step 2: Applying the Coulombic potential energy

The decrease in atomic radius and the increase in nuclear charge going from left to right in a period both cause the energy required to remove an electron, also known as the ionization energy, to increase. The equation of Coulombic Potential Energy, \(U = k*Q1*Q2/d\), perfectly describes this phenomenon. Here, 'Q1' and 'Q2' are the charges of a nucleus and an electron, and 'd' is the distance between them. Given that 'Q1' increases and 'd' decreases, the energy 'U' will increase.

Step 3: Summary

So, as we move from left to right across a period, the number of protons in the atom increases, which increases the positive charge of the nucleus and attracts the electrons more strongly. This stronger attraction (higher nuclear charge and smaller radius) means that more energy is required to remove an electron, thus the ionization energy increases.