Definition of Ionization Energy in Chemistry
Ionization energy or ionization potential in chemistry is the amount of energy required to remove the outer electron of an isolated gaseous atom present in the periodic table chemical elements. The periodic table trend of ionization energy or potential affecting mainly by factors like atomic radius, atomic number, filled or half-filled orbitals, shielding electron, and charge or oxidation number of elements for learning chemistry. The electron is raised to a higher energy level by absorption of energy from external sources and if the ionization process continued, a stage comes where the electron goes fully out of the influence of the atomic nucleus. Therefore, the processes where an atom produces a cation by the removal of the electron is defined as ionization energy, calculated from the required energy to complete this process
Ionization Energy Formula
Electrons are raised to higher energy levels by the transfer of energy from external sources. But if energy transfer to electron particles sufficient, electrons go fully out of the influence of the nucleus of atoms. Therefore, M(g) + IE → M+(g) + e. The ionization energy or enthalpy of the periodic table element is an endothermic reaction in thermodynamics because during the process energy is consumed by atoms generally represented I or IE and find by unit electron volt (eV) per atom or Kcal/mol or kJ/mol.
Electron volt to joule conversion
For the conversion of electron volt to joule, first, we define electron volt. The energy consumption by an electron falling through a chemical potential difference of one volt is defined as an electron volt (eV), the units of ionization energy.
∴ 1 eV = charge of an electron × 1 volt
= (1.6 × 10-19 coulomb) × (1 volt)
= 1.6 × 10-19 Joule
1 eV = 1.6 × 10-12 erg
Ionization Energies of Element
The amount of energy required for removal of the first electron from a gaseous atom is called its first ionization or M (g) + IE1 → M+ (g) + e. But if the energy consumption for removal of the second electron from a cation called second ionization or M+ (g) + IE2 → M+2 (g) + e. Similarly, we have to define the term third, the fourth ionization energy of periodic table elements.
How to calculate ionization energy of hydrogen atom?
The energy transfer for completely removing an electron from hydrogen energy levels is called ionizing energy of hydrogen atom. Simply the ionized energy corresponding to the electromagnetic transition from n = ∞ to n = 1, measure the ionization energy of the hydrogen atom from Bhor energy equation, EH = 2.179 × 10-11 erg = 2.179 × 10-18 Joule = 13.6 eV.
Ionization of Helium Atom
The electron configuration of helium 1s2. Therefore, the second ionization energy finds by the removal of the second electron from the 1s orbital against the nuclear charge of +2 and calculated from Bhor energy equation, IEHe = Z2 × IEH= 22 × 13.6 eV = 54.4 eV.
Periodic Table Trends of Ionization Energy
Atomic Radius in Periodic Table
The greater the atomic radius of elements in the periodic table, the weaker will be the attraction. Hence the required energy for the removal of the electron lower. If an atom is raised to an excited state by promoting one electron to a higher quantum level, the excited electron is more easily detached because the distance between the electron and nucleus increases.
Atomic Radius of Elements
The atomic radius decreases from left to right along a period in the periodic table. Therefore, when we move left to right along a period in the periodic table, ionization energy trends normally increase because the atomic radius decreases but when we moving from top to bottom in a group the value of potentials of chemical elements decreases with the increasing size of the atom.
Atomic Number and Ionization Energy
With the increasing atomic number, the charge on the nucleus increases, and more difficult to remove an electron from an atom. Normally the term ionization energy trend increases with the increasing atomic number or moving from left to right in a period of the periodic table. Because with the increasing atomic number, the change in the nucleus also increases. Therefore, the electrostatic attraction between the outermost electrons and the nucleus of an atom also increases and the removal of an electron from the nucleus is more difficult.
Half-filled and filled Orbitals
According to Hund’s rule, half-filled or fully-filled orbital comparatively low energy or more stable. Hence for such an atom, more energy is required to remove an electron. Therefore, such calculation of ionization energy of an atom greater than the expected value calculated from the formula.
Exceptions of Ionization Energy Trends
Few exceptions in the value of the ionization energy trends in the periodic table are explained based on the half-filled and fully-filled orbitals. Group-15 elements have higher ionization potential than the group-16 elements and group-2 elements have higher than the group-3 elements in the periodic table. For example, the measure first ionization energy of nitrogen greater than oxygen and phosphorus greater than sulfur.
Nitrogen and phosphorus in group-15 elements with atomic numbers 7 and 15, have the electron configuration, 1s2 2s2 2p3 and 1s2 2s2 2p6 3s2 3p3 respectively. Therefore, the removal of an electron from half-filled 2p and 3p-orbital of nitrogen and phosphorus required more ionization energy. Removal of an electron from the group-2 element of beryllium (Be) and magnesium (Mg) with fully-filled s-orbital required more ionisation energy.
Shielding Electron of Atom
Electrostatic attraction between the electrons and nucleus shows that an outer electron is attracted by the nucleus and repelled by the electrons of the inner shell. This combines attractive and repulsive force acting on the outer electron experiences less attraction from the nucleus. Thus this effect is known as the shielding effect.
The larger the number of electrons in the inner shell, the lesser the attractive force for holding the outer electron. Hence the radial distribution functions of the s, p, d subshell show that for the same principal quantum number the s-subshell most shielding than the p-subshell and least shielding the d-orbital. The shielding efficiency, s〉p〉d. But as we move down a group, the number of inner-shells increases, and hence the determine ionization potential tends also decreases. For example, the measure ionisation potential trend for group-2 elements, Be〉Mg〉Ca〉Sr〉Ba.
Ionization Energies Trends in Periodic Table
The greater the charge on the nucleus of an atom the more energy required for removing an electron from the atom. But with the increasing atomic number electrostatic attraction between the outermost electrons and the nucleus of an atom increases. Therefore, the ionizing of an atom difficult in chemistry, and the value of ionization energy generally increases in moving left to right in a period.
Due to the presence of a fully-filled and half-filled orbital of beryllium and nitrogen, the ionization energy of beryllium and nitrogen slightly higher than the neighbor element boron and oxygen. Thus the ionization trends in the periodic table for the second period, Li ㄑ B ㄑ Be ㄑ C ㄑ O ㄑN 〈F ㄑ Ne.
Charge on Nucleus and Ionization Energy
An increase in the overall charge on the ionizing species (M+, M+2, M+3, etc) will enormously influence the ionization. During ionization, electron withdrawal from a positively charged species more difficult than from a neutral atom. But the first ionization potential chart of the elements varies with their positions in the periodic table. In each of the tables, the noble gas has the highest value and alkali metals crystals have the lowest value of determining ionization energy.
Chemical Properties of Ionizing Species
In learning chemistry, the measure ionization potential in for the particular group is an impotent property of periodic table elements. Therefore, lithium, sodium, potassium, rubidium, cesium, and alkaline earth metal have a low value of ionization energy. Therefore, in science, the reactivity of alkali alkaline metals for the formation of polar molecules with ionic bonding is greater than the other elements of the periodic table.
The lower the value of ionization energy or potential, the greater is the reducing power of the elements in the redox reactions because the removal of an electron from the chemical elements would mean oxidizing reaction. Therefore, with the decreasing ionizing power, the base properties of elements also increase, and acid properties decrease. The ionization energy chart also used to calculate chemical bond energy, electronegativity, and electron affinity of the periodic table elements by Mulliken.