Ionization Enthalpy

Introduction

Ionization energy (I.E.) is described as the minimum (min) required energy (e) to remove (throw out) the most loosely (weakly) bounded electron (e) of an isolated gaseous (g) atom, +ve ion, or molecule. Ionization energy (I.E) follows periodicity in the modern periodic table. The normal or general trend is that the ionization energy (I.E) increases on moving from left (l) to right (r ) across the period (p). And, on moving from the top (t) to bottom (b) across a group (g), ionization energy decreases or reduces. There are also certain exemptions to (I.E.) ionization energy.

What is Ionization Energy ?

Ionization energy simply can be defined as the measure of the toughness or difficulty in removing (throwing out) an electron (e) from any atom or ion or it can also be considered as the tendency (ability) of an atom (a) or ion to remove an electron (e). The loss (lack) of electron (e) usually occurs at the chemical species' ground state.

The ionization energy (I.E.) is the measurement of strength or capability (attractive forces) by which an electron occupies its position. Ionization energy can also be described as the minimum (min) energy that an electron in a gaseous (g) atom or ion needs to be absorbed to come out of the (force) influence of the nucleus. Sometimes, it is also considered ionization potential and it is an endothermic process.

Ionization Energy Formula

Ionization energy or potential for the simplest element that is hydrogen (H) can be determined or calculated or find out using (performing) the following equation −

$$\mathrm{E= hcR_H (1/n^2), where}$$

E denotes the energy (e) of the electron (e) or the quantity of energy (e) it takes (requires) to remove (throw out) the electron (e), ionization energy (I.E.), h denotes the Planck’s constant, and its value= 6.626×10^-34 Js (joules second), c represents the speed (s) of light and it is a constant term whose value = 3.0*10⁸ m/s, R_H denotes the Rydberg constant = 1.097×10⁷ m^-1, and n is the principal (p) quantum (q) number or we can say the energy (e) level of the electron (e). Now, after putting all these values in the equation, we will get − $\mathrm{ E=(2.18*10^{-18} J)(1/n^2)}$.Ionization Energy Trend in the Periodic Table

General trends in the ionization energy are

• Trends in the ionization energy in a group − The ionization energy (I.E.) or the first (1st) I.E. of elements decreases (reduces) as we from the top (t) to bottom (b) in a group, since the atomic no. increases down the group, and the number of shells (s) also increases. outermost electrons (e) become far away from the nucleus and thus become easy to remove.

• Trends in the ionization energy across a period − As we move (displace) from left (l) to right (r ) along a period (p), the ionization energy (I.E) of the elements (e) increases. This is because of the decrease in the size (s) of the atoms (a) across a period. Here, the valence electron (e) becomes closer to the nucleus of an atom due to increased nuclear charge.

First, second, and Subsequent Ionization Energy

• First (1st) ionization energy − It is described as the energy (e) needed to remove (throw out) the outermost (o) or we can say the highest (higher) energy electron (e) from a neutral atom (a) in the gas (g) phase.

• Second ionization energy − It is described as the energy (e) needed to remove (throw out) the outermost or we can say that the least bounded electron (e) from a 1+ ion of the element (e). The second (2nd) ionization energy (e) of an element is always found to be higher than the first.

• Subsequent Ionization energy − It is described as the energy (e) that is required or needed to remove the electrons (e) one after the another. It also depends on the no. of electrons (e) present (found) in the extreme or outermost (o) shell.

Exemptions to the Ionization Energy Trend

Broadly, there are two exceptions to the ionization energy trend. The first (1st) ionization energy (I.E.) of boron (B) is less than that of beryllium (Be) and also the first (1st) ionization energy (I.E.) of oxygen (O) is less than that of nitrogen (N). The reason behind this discrepancy is the electronic configuration of these elements and the well-known Hund’s rule.

Valency

Valency is defined or described as the capability or ability of an atom or a group of atoms to form bonding (chemical) with another atom (a) or a group of atoms. The valence or valency of an element can be determined by the number (no.) of electrons (e) at the outermost shell or valence shell.

Valency and its Periodic Trends

• Group 1 elements have only one valence (v) electron (e), so they possess a valency (v) of +1 because they are about to give or lose 1 electron (e).

• Similarly, group 2 elements can lose 2 electrons (e), and group (gr) 3 elements can lose 3 electrons.

• Group-5 elements contain 5 valances (v) electrons and it will tend to take only 3 of them, thus having a valency (v) of -3.

• Similarly, group-6 (VI) elements (e) have a valency of -2, group-7 elements occupy a valency (v) of -1, and group-8 (VIII) elements (e) do not (doesn’t) react and therefore have a valency or value = 0.

Conclusion

Ionization energy denoted by (I.E.) is described as the minimum (min) required energy (e) to remove (throw out or lose) the most loosely (weakly) bounded electron (e) of an isolated gaseous (g) atom, +ve ion, or molecule. Ionization energy (I.E) follows periodicity in the modern periodic table. The normal or general trend is that the ionization energy (I.E) increases on moving from left (l) to right (r ) across the period. And, on moving from the top (t) to bottom (b) across a group (g), ionization energy decreases or reduces. There are also certain exemptions to (I.E.) ionization energy.

FAQs

1. What do you mean by isolated gaseous atoms?

An isolated gaseous atom is defined as an atom (a) that is free from any other atoms in the gaseous (g) state.

2. Define Periodicity.

The periodical (p) repetition of the similar (same) properties of the elements (e) after certain intervals of time, when the elements (e) are kept or arranged in terms of increasing (inc) Z (atomic number) is called periodicity.

3. Describe Hund’s Rule.

Hund’s rule describes that every (individual) orbital (o) in a subshell (s) is singly (1) filled by one electron (e) before any one (1) orbital (o) is doubly (2) filled, and all electrons (e) in the singly (1) filled orbitals (o) have the similar spin.

4. Across a period, ionization energy increases or decreases.

Across a period, ionization energy (I.E.) increases.

5. Ionization energy is which type of process?

Ionization energy is always an endothermic process.