Periodic Trends in Ionisation Enthalpy of Elements - Overview, Structure, Properties & Uses

Periodic Trends in Ionisation Enthalpy of Elements - Overview, Structure, Properties & Uses

What is Ionization Enthalpy/Define Ioniztion Energy/Define Ionization Enthalpy/Define Ionisation Enthalpy?

Ionization Enthalpy Definition or Ionisation Enthalpy Definition: Ionization enthalpy meaning is the amount of energy required by an isolated gaseous atom to lose an electron in its ground state is known as ionization energy, or ionization enthalpy of elements. Cation formation is the outcome of electron loss. The energy required to detach one mole of electrons from one mole of isolated gaseous ions or atoms is known as the initial/first ionization energy of a molecule/atom.

Ionization Energy of First, Second, and Subsequent Ones/What is Ionisation Enthalpy

The energy required to remove the next electron is the second ionization energy, and so on. At the same time, when compared to the first ionization energy, the second ionization energy is always higher. An alkali metal atom, for example, can be used. Because its loss gives the atom a stable electron shell, removing the first electron is comparatively simple. In addition, removing the second electron creates a new electron shell that is closer to the atomic nucleus and more closely linked.

The following equation can be used to express the first ionization energy of hydrogen:

H (g) → H+ (g) + e-

ΔH° = -1312.0 kJ/mol

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Factors Affecting the Ionization Energy

Ionization energy is principally determined by two factors:

  1. Electron repulsion force.

  2. The nucleus and electrons are attracted to each other.

When compared to the actual nuclear charge, the effective nuclear charge, which is sensed by the outermost electrons, will be lower. As the inner electrons will obstruct the nuclear charge path, the outermost electrons will be shielded. The shielding effect is the name given to this phenomenon.

Ionization Energy Trend in Periodic Table

General Periodic Trends

It diminishes while moving from the top to the bottom of a group.

  1. It gradually grows from left to right over time.

Trends in Ionization Enthalpy in a Group

As proceeded down in a group, the first ionization enthalpy of the elements drops. Moving down in a group, on the other hand, increases the atomic number and thus the number of shells. The outermost electrons are far distant from the nucleus and can thus be easily removed. The shielding effect as we proceed down a group due to an increased number of shells is the second or another factor that reduces the ionization energy.

Trends in Ionization Enthalpy Across a Period

The ionization energy of an element increases when moved from left to right over time. This occurs as the size of atoms decreases over time. Because of the higher nuclear charge, the valence electrons get closer to the atom's nucleus as we proceed from left to right. As the attraction force between electrons and the nucleus grows stronger, it takes more energy to remove an electron from the valence shell. Two deviations to the pattern appear to be clearly obvious in the first ionization energies figure. Boron's initial ionization energy is lower than that of beryllium, and oxygen's first ionization energy is lower than that of nitrogen. The Hund's rule and the electron configuration of these atoms are to blame for the disparity. Although the boron ionization requires a 2p electron, the first ionization potential electron for beryllium comes from the 2s orbital. The electron comes from the 2p orbital in both oxygen and nitrogen.


The ability of an atom or a group of chemically connected atoms to create chemical connections with other atoms or groups of atoms is referred to as valence. The number of electrons in an element's outer shell determines its valence (valence). The valence of polyatomic ions is the charge on the particle (such as SO42-).

Valency and its Periodic Trends

The periodic table divides elements into groups (columns) based on the number of valence electrons they have, therefore the item's position in the table will give an indication of its valence.

As they tend to give away one electron, both group 1 elements have one valence electron and so have a +1 valence.

The same holds true for group 2 losing two electrons and group 3 losing three electrons.

Group 5 elements, on the other hand, have 5 valence electrons and will tend to take 3 electrons, giving them a valence of -3.

The elements in Group 6 have 6 valence electrons, which tend to take 2 electrons and have a valence of -2.

Components in Group 7 contain 7 valence electrons, while those with a valence of -1 are more likely to take one electron.

Group 8 elements do not react, hence their value is zero

Key Points

Let's have a look at the important critical points related to the periodic changes in ionization enthalpy:

  1. Electron volts (eV) and kilojoules per mole (kJ/M) are the two most used unit of ionization energy.

  2. In the gas phase, ionization energy is defined as the minimal energy required to remove an electron from an ion or an atom.

3. Over the course of an element period, the ionization energy tends to rise as it moves from left to right. The atomic radius, on the other hand, diminishes as one moves from left to right over time. As a result, electrons are drawn closer to the nucleus.

4. Ionization energy has a regular pattern on the periodic table.

  • While moving down a ionization energy periodic table group from top to bottom, the ionization energy tends to decrease. Moving down a group, however, a valence shell can be added. Furthermore, because the outermost electrons come from a positively charged nucleus, they are easier to remove.

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