# Ionization Energy: Types, Factors, Calculation, Trends Exceptions (2023)

It is the energy required to strip one or more electrons from a neutral atom to create a positively charged ion, which alters the atom’s chemical behavior.

The ionization energy (I.E.) is necessary to remove one or more electrons from a neutral valence to produce a positively charged ion and change the atom’s chemical properties.

It is often expressed in kJ/mol, and the measurement is based on an individual gaseous atom.All elements in the periodic table have a characteristic known as ionization energy, sometimes known as ionization potential.

I.E. can be represented as shown

• X + first ionization energy → X+ + e-

Where

• X is a neutral atom.
• X+ is an ion of atom X with a single positive charge.
• eis an electron with a single negative charge.

## Types of Ionization Energy

### First Ionization Energy

The “first ionization energy”of an element refers to the energy needed to remove the outermost valence electron from a neutral atom in the gas phase.

In the equation, it refers to the I.E. required to remove a neutral atom’s first electron, giving an ion with a single positive charge. The process by which the first I.E. of sodium is measured would be represented by the following equation:

(Video) The Periodic Table: Atomic Radius, Ionization Energy, and Electronegativity

Na (g) + energy Na+ (g) + e

### Second Ionization Energy

The second ionization energy is required to remove the next electron, which is always higher than the first ionization energy because it requires even more energy to remove an electron from a cation than it does from a neutral atom.

For an alkali metal atom, since its loss gives the atom a stable electron shell, removing the first electron is quite simple. Removing the second electron involves forming a new electron shell that is tighter and more closely connected to the atomic nucleus.

The process by which the second I.E. of sodium is measured would be represented by the following equation:

Na (g) + energy Na2+ (g) + e

### Third Ionization Energy

The “third ionization energy”of an element refers to the energy needed to remove third electron. It is required to form 3+cations.

The process by which the third I.E. of sodium is measured would be represented by the following equation:

Na2+ (g) + energy Na3+ (g) + e

All elements have first-ionization energy, even atoms, which do not form positive ions in test tubes.

Throughout the periodic table, the first ionization energy fluctuates constantly. The I.E. decreases from top to bottom in groups and rises from left to right across a period. Therefore, helium has the highest first ionization energy, whereas francium has one of the lowest.

## Factors That Affect The Size Of Ionization Energy

Ionization energy is a unit of measurement for the force required to eject a certain electron from the nucleus’s gravitational pull. A high value of I.E. shows a high attraction between the electron and the nucleus. The size of that attraction will be determined as follows:

(Video) Periodic Trends: Electronegativity, Ionization Energy, Atomic Radius - TUTOR HOTLINE

Distance Of the Electron from the Nucleus:

The distance between the electrons and the nucleus affects the attraction. It rapidly declines with an increase in space. An electron closer to the nucleus is more strongly attracted than one further away.

Nuclear charge:

When the number of protons in the nucleus increases, its positive charge increases, and vice versa. Electrons tend to be strongly attracted to positively charged nuclei.

Number Of Electrons between the outermost electrons and the nucleus:

Let’s take a look at sodium atoms with the electronic structure 2,8,1.

Between the outer electron and the nucleus are the two layers of electrons. The 11 protons in sodium’s nucleus have their effects cut down by the inner electrons. The outer electron only feels a net pull of approximately 1+ from the center. This lessening of the force of the nucleus by inner electrons is known as screening or shielding.

Penetration Effect of Electron
A single atom can contain a variety of subshells, including the s, p, d, and f subshells. As opposed to p-subshell and other subshells, the s-subshell is, as is well known, located closer to the nucleus. In contrast to the other subshells, the s-subshell has a stronger affinity to the nucleus, making it more difficult to remove electrons from it. Therefore, to remove electrons from the s-subshell, additional ionization energy is needed.

Fully and Half-filled electrons

I.E is greater in fully filled orbitals than in half-filled or partially filled orbitals. Partially filled orbitals are less stable than fully filled orbitals.

## Calculating Ionization Energy

The following equation can be used to calculate the ionization potential of hydrogen:

(Video) Ionization Energy - Basic Introduction

E = h c RH ( 1/n2), where

• E is the energy of the electron (or the amount of energy it takes to remove the electron, ionization energy)
• hisPlanck’s constant= 6.626 * 10-34Js (joules seconds)
• cis the speed of light = 3.00 * 108m/s (meters/second)
• RHisRydberg constant= 1.097 * 107m-1(1/meters)
• n is the principalquantum number (or energy level) of the electron

After applying the values of constants, the equation becomes:

E = (2.18 * 10-18J)(1/n2)

From here, you can enter the electron’s energy level value to calculate how much power is required to remove it.

## Ionization Energy Unit

Ionization energy is typically represented in kcal/mol, kJ/mol, or electron volts (eV) per atom. Mathematically,

A single electron volt (eV) is 3.827*10-20 per atom.

= 3.827 x 10-20x 4.184 cal per atom (∵cal=4.184 J)

= 1.602 x 10-19J per atom

= 1.602 x 10-19x 6.022 *1023J/mol

= 96472 J mol-1

= 96.472 kJ mol-1

(Video) Exception to the Ionization Energy Trend

## Ionization Energy Trend On Periodic Table

• Moving from left to right across an element period (row), ionization energy normally increases. The reason for this is that the atomic radius decreases as one moves through a period. This occurs as more protons are supplied, increasing the nucleus-electron attraction and pushing the electron shells closer.
• Ionization energy generally decreases moving from top to bottom down an element group (column) as the principal quantum number of the outermost (valence) electron increases moving down. Atoms have more protons moving down a group, which does pull in the electron shells. The outermost electrons are even farther from the nucleus since each row adds a new shell.
• Helium, one of the noble gases, has the highest ionization energy and is found in the upper right corner of the periodic chart. Francium, an alkali metal on the far left side of the chart, has one of the lowest ionization energies.
• Typically, group 2 elements have ionization energy greater than group 13 elements and group 15 elements have greater ionization energy than group 16 elements.
• Groups 2 and 15 have completely and half-filled electronic configuration respectively, thus, it requires more energy to remove an electron from completely filled orbitals than incompletely filled orbitals.
• Alkali metals (IA group) have small ionization energies, especially when compared to halogens or VII A group.

## Exception of Ionization Energy Trend on Periodic Table

• Boron has a lower first I.E. than beryllium. Comparing their electronic configuration we can analyze the differences in their ionization energy. Boron with outer electrons in ‘s’ orbital is very close to the nucleus whereas, beryllium releases its first electron from the p-orbital which is comparatively far from the nucleus.
• Nitrogen has three electrons in the p orbital while oxygen has four electrons. Nitrogen should have lower I.E but on contrary, it has lower first ionization energy than oxygen because of the symmetrical distribution of three electrons in the p orbital of a nitrogen atom, by Hund’s rule. The other reason for this exception is electron-electron repulsion.
• Lanthanides and actinides have lower ionization energies due to the presence of an inner ‘f’ electron shell.

• 5 Important Periodic Trends
• Periodic Table of Elements- Definition, Terms, 118 Elements
• What are Valence Electrons?
• Lattice Energy: Calculation, Trend, Formula
• Electrode Potential: Types, Importance, and Applications

## 1st, 2nd, and 3rdIonization Energies

• I1 = first ionization energy(energy required to take away an electron from a neutral atom)
• I2 stands for the second ionization energy(energy required to take away an electron from an atom with a +1 charge.

Each succeeding ionization energy is larger than the preceding energy.

This implies I1<I2<I3<…<In will always be true.

Here is an example showing how ionization energy increases as succeeding electrons are ejected.

Mg (g) → Mg+(g) + e I1 = 738 kJ/mol

Mg+(g) → Mg2+ (g)+ e I2 = 1451kJ/mol

See first, second, and third ionization energies of elements/ions

## References

• F. Albert Cotton and Geoffrey Wilkinson,Advanced Inorganic Chemistry(5th ed., John Wiley 1988) p.1381.
• Lang, Peter F.; Smith, Barry C. “Ionization Energies of Atoms and Atomic Ions”. Journal of Chemical Education. 80 (8).
• Cotton, F. Albert; Wilkinson,Geoffrey (1988).Advanced Inorganic Chemistry(5th ed.). John Wiley. ISBN0-471-84997-9.
• Housecroft, C.E.; Sharpe, A.G. (November 1, 1993).Inorganic Chemistry(eBook). Inorganic Chemistry. Vol.3 (15thed.). Switzerland: Pearson Prentice-Hall. pp.536, 649, 743.
• https://brilliant.org/wiki/ionization-energy/
• https://chemistrytalk.org/ionization-energy-trend/

## FAQs

### What are the exceptions to the ionization energy trend? ›

Exceptions to this trend is observed for alkaline earth metals (group 2) and nitrogen group elements (group 15). Typically, group 2 elements have ionization energy greater than group 13 elements and group 15 elements have greater ionization energy than group 16 elements.

What are the exceptions for ionization energy in period 3? ›

However, the trend has two anomalies. The first is between Mg and Al, because the outer electron of Mg is in the orbital 3s, whereas that of Al is in 3p. The 3p electron has more energy than the 3s electron, so the ionization energy of Al is actually less than that of Mg.

What are the factors which influence the ionization energy answer? ›

Ionization energy depends on two factors: The force of attraction between electrons and the nucleus. The force of repulsion between electrons.

What are the two factors that affect the trends for the ionization energy? ›

FACTORS AFFECTING IONIZATION ENERGY
• SIZE OF THE ATOM: The distance between the nucleus and the electrons is inversely related to the attractive force connecting them. ...
• NUCLEAR CHARGE: The nucleus exerts a stronger pull on the valence shell electrons as the degree of nuclear charge increases. ...
• ELECTRONIC CONFIGURATION:

Are there exceptions to the periodic trends? ›

Group 8A atoms are an exception to the periodic trend rule. Group 8A atoms belongs to zero group elements or inert gases or Noble gases. These elements generally do not participate in chemical reactions.

Are there any exceptions to the trend in electronegativity? ›

From top to bottom down a group, electronegativity decreases. This is because atomic number increases down a group, and thus there is an increased distance between the valence electrons and nucleus, or a greater atomic radius. Important exceptions of the above rules include the noble gases, lanthanides, and actinides.

Are there any exceptions to the atomic radius trend? ›

The atomic radius of atoms generally decreases from left to right across a period. There are some small exceptions, such as the bismuth (Bi) radius being slightly greater than the polonium (Po) radius.

What does ionization not depend on? ›

The degree of ionization depends on nature of electrolyte, dilution of electrolyte, and temperature but does not depend on the volume of electrolyte.

What are the exceptions to electron configuration? ›

There are two main exceptions to electron configuration: chromium and copper. In these cases, a completely full or half full d sub-level is more stable than a partially filled d sub-level, so an electron from the 4s orbital is excited and rises to a 3d orbital.

What is the trend of ionization energy? ›

What is the trend for ionization energy? The general trend of ionization energy in a periodic table is that the energy increases as you move in the direction of hydrogen to helium and decreases as you move from hydrogen to cesium.

### Which of the following will not affect ionization energy? ›

Shielding effect does not have any effect on I.P.

What factor is not affecting ionization enthalpies? ›

Electron is removed from an isolated neutral gaseous atom and so type of bonding in the crystalline lattice is not associated with ionization enthalpy.

What are the factors that influence ionization energy and explain any three of them? ›

The factors that influence the ionisation energies are : the size of the atom. the charge on the nucleus. how effectively the inner electron shell screen the nuclear charge.

What are the 3 factors that affect atom size ionization energy and electronegativity? ›

There are three factors that help in the prediction of the trends in the Periodic Table: number of protons in the nucleus, number of shells, and shielding effect.

What are the 2 types of ionization energy? ›

Ionization of molecules often leads to changes in molecular geometry, and two types of (first) ionization energy are defined – adiabatic and vertical.

What elements are exceptions to the periodic law? ›

Exceptions to the States of the Periodic Table
• Mercury. The shiny metal Mercury at room temperature unlike all metals in the periodic table exists as a liquid. ...
• Bromine. Again another liquid in the periodic table, located in Group 7 Bromine is the only other known liquid in the periodic table. ...
• Carbon.

Why are trends and exceptions to the trends in ionization energy observed? ›

Why are the trends and exceptions to the trends in ionization energy observed? The ionization energies of elements in Group 13 tend to be lower than the elements in Group 2 because the full s orbital shields the electron in the p orbital from the nucleus.

What are the exceptions of elements in periodic table? ›

Two elements like hydrogen and helium are observed as an exception .

What are the two factors that affect the trends for the electronegativity? ›

An atom's electronegativity is affected by both its atomic number and the distance at which its valence electrons reside from the charged nucleus.

What elements are excluded from electronegativity? ›

Since electronegativity measures the amount of attraction between an atom and an electron, noble gases do not have electronegativity.

### What is the exception to electron gain enthalpy? ›

Exception in Electron Gain Enthalpy

In the case of Fluorine and Chlorine, Chlorine contains a higher negative electron gain enthalpy value. Whereas, to define electron gain enthalpy of oxygen, in between Oxygen and Sulphur, Sulphur contains a higher negative value than oxygen.

What are the exceptions to the transition metal rule? ›

Many of the transition metals (orange) can have more than one charge. The notable exceptions are zinc (always +2), silver (always +1) and cadmium (always +2).

Do atomic and ionic radius have the same trend? ›

Ionic radii follow the same vertical trend as atomic radii; that is, for ions with the same charge, the ionic radius increases going down a column. The reason is the same as for atomic radii: shielding by filled inner shells produces little change in the effective nuclear charge felt by the outermost electrons.

Does ionization energy depend on temperature? ›

Summary: Ionization and Surface Temperature and Density

The higher the temperature, the more likely that higher states of ionization are produced.

Why are there inconsistencies in ionization energy? ›

These inconsistencies are attributed to the actual type of orbital the electron is being removed from. For instance, a 2p orbital has a higher energy than a 2s. The ionization energy of an atom is equal to the amount of energy given off when an electron is added to an atom.

What are exceptions in atomic structure? ›

However, there are three general exceptions to the octet rule: Molecules, such as NO, with an odd number of electrons; Molecules in which one or more atoms possess more than eight electrons, such as SF6; and. Molecules such as BCl3, in which one or more atoms possess less than eight electrons.

What are the exceptions to electron affinity and why? ›

Exceptions to electron affinity trends include the noble gases, fluorine and Groups 2, 14 and 15 in the periodic table.

What are the exceptions of 18 electron rule? ›

A few common examples of exceptions to 18 electron rules include: 16-electron complexes: The metal center is usually low-spin and is in d8 configuration. These complexes adopt square planar structure, such as Rh(I), Ni(II), Pd(II), and Pt(II) complexes.

What is an example of ionization energy? ›

The first ionization energy of sodium, for example, is the energy it takes to remove one electron from a neutral atom. The second ionization energy is the energy it takes to remove another electron to form an Na2+ ion in the gas phase.

What is meant by ionization energy? ›

ionization energy, also called ionization potential, in chemistry and physics, the amount of energy required to remove an electron from an isolated atom or molecule.

### What is the trend for ionization energy with atomic number? ›

Within a group, the ionization energy decreases as the size of the atom gets larger. On the graph, we see that the ionization energy increases as we go up the group to smaller atoms. In this situation, the first electron removed is farther from the nucleus as the atomic number (number of protons) increases.

Which is incorrect about ionization energy? ›

The incorrect statement about Ionization Energy is 'It decreases in a Period ' i. e. Option 'C'. Ionization Energy is the amount of energy required to remove an electron from an isolated gaseous atom.

What are the factors affecting electron affinity and ionization energy? ›

The three factors affecting the electron affinity of a molecule are Nuclear Charge, Atomic Size, and Electronic Configuration.

On what factor does ionization enthalpy depend? ›

Ionization enthalpy depends on the following factors: Penetration effect. Shielding effect. Electronic configuration.

What elements increase ionization energy? ›

The ionization energy decreases from top to bottom in groups, and increases from left to right across a period. Thus, helium has the largest first ionization energy, while francium has one of the lowest.

What are three factors which influence the size of an atom or ion? ›

These factors are: The number of protons in the nucleus (called the nuclear charge). The number of energy levels holding electrons (and the number of electrons in the outer energy level). The number of electrons held between the nucleus and its outermost electrons (called the shielding effect).

How does charge affect ionization energy? ›

As the nuclear charge increases, its attraction for the outermost electron increases and more energy is required to remove an electron. This means that the ionisation energy increases.

What are the exceptions to electron affinity and ionization energy? ›

Exceptions to electron affinity trends include the noble gases, fluorine and Groups 2, 14 and 15 in the periodic table.

Are there any exceptions to the ionic radius trend? ›

Note that there are some exceptions to this trend. For example, oxygen's radius is actually a little larger than nitrogen's radius. This effect is extremely notable with the metal elements, as they and up forming cations.

Why is oxygen an exception to the ionization energy trend? ›

The last electron in the oxygen atom is forced into an already occupied orbital where it is kept close to another electron. The repulsion between these two electrons makes one of them easier to remove, and so the ionization energy of oxygen is lower than might be expected.

### What are the exceptions to electron? ›

There are two main exceptions to electron configuration: chromium and copper. In these cases, a completely full or half full d sub-level is more stable than a partially filled d sub-level, so an electron from the 4s orbital is excited and rises to a 3d orbital.

Why are the exceptions to electron affinity? ›

In general, exceptions arise when new subshells are being filled/half-filled, or in cases where the atom is too small. In the first case, Be and Mg are interesting examples: they have a positive electron affinity (just like N, in fact) because of the energy difference between the s and p subshells.

Why is nitrogen an exception to the electron affinity trend? ›

Since N has half-filled p-orbital which provides extra stability. So it has lower electron affinity than carbon.

What are the exceptions to ionic bonds? ›

Two metals can't form an ionic bond. The requirements for this bond are the losing of electrons by one element and gaining by another. There is no metal in existence that accepts electrons. So, ionic bond between only metals is not possible.

What are the exceptions of ionic charge? ›

The notable exceptions are zinc (always +2), silver (always +1) and cadmium (always +2).

What are the exceptions of the metallic trend? ›

Metallic character is displayed by metals, which are all on the left-hand side of the periodic table. The exception is hydrogen, which is a nonmetal under ordinary conditions. Even hydrogen behaves as a metal when it's a liquid or solid, but you should consider it nonmetallic for most purposes.

What is the trend for ionization energy required? ›

The ionization energy decreases from top to bottom in groups, and increases from left to right across a period.

Why is oxygen an exception to atomic radius? ›

Oxygen, however, has an electronic configuration of 2p4, having one paired electrons in one of its orbittals. This leads to inter-electronic repulsion and thus increases the atomic radius slightly.

How does ionization energy increase? ›

On the periodic table, first ionization energy generally increases as you move left to right across a period. This is due to increasing nuclear charge, which results in the outermost electron being more strongly bound to the nucleus.

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