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Updated on 24th August, 2023 , 8 min read
Ionization enthalpy, also known as ionization energy, is an essential concept in chemistry and physics. It refers to the amount of energy required to remove an electron from an atom or ion in its gaseous state. In this article, we will explore the definition of ionization enthalpy, the trends observed in the periodic table, and the various applications in different fields of science.
In thermochemistry, enthalpy is the heat content of a system. It is the sum of the internal energy of the system plus the product of its pressure and volume. Enthalpy is a state function. The SI unit of enthalpy is the joule.
A quantity related to a thermodynamic system that is equal to the heat transmitted during an isobaric process and is expressed as the system's internal energy plus the product of the system's pressure and volume. h is the symbol for enthalpy.
Ionization energy is the amount of energy required to remove an electron from an atom or molecule. The higher the ionization energy, the more difficult it is to remove an electron. The first ionization energy is always greater than the second ionization energy, which is always greater than the third ionization energy, and so on.
In a liquid solution, ionization is common. For example, at the surface of a piece of metallic zinc in contact with an acidic solution, neutral hydrogen chloride gas molecules, HCl, react with similarly polar water molecules, H2O, to produce positive hydronium ions, H3O+, and negative chloride ions, Cl-; zinc atoms, Zn, lose electrons to hydrogen ions and become colorless zinc ions, Zn2+.
Ionization enthalpy is a measure of the amount of energy required to remove an electron from an atom or ion in its gaseous state. The ionization energy is measured in electron volts (eV) or kilojoules per mole (kJ/mol). It is an essential property of an atom or ion that is influenced by various factors such as the atomic radius, electron shielding, and nuclear charge.
Ionization Enthalpy | Definition | Sign | Trend |
| Ionization Enthalpy | The amount of energy required to remove a single electron from the ground state of a gaseous atom (X) | Always positive | Increases across periods, decreases down groups. |
The table below explains the relationship between Enthalpy and Ionization energy.
Property | Enthalpy | Ionization Energy |
| Definition | Enthalpy is the measure of the heat energy exchanged between a system and its surroundings during a constant-pressure process. | Ionization energy is the minimum amount of energy required to remove an electron from a gaseous atom or ion in its ground state. |
| Formula | ∆H = H_final - H_initial | IE = energy required to remove an electron |
| Unit | Joules (J) or kilojoules per mole (kJ/mol) | Electronvolts (eV) or kilojoules per mole (kJ/mol) |
| Sign | ∆H can be positive or negative, depending on whether the reaction is exothermic or endothermic. A positive ∆H indicates an endothermic reaction, where the system absorbs heat from the surroundings. A negative ∆H indicates an exothermic reaction, where the system releases heat to the surroundings. | Ionization energy is always positive, indicating that energy must be added to the system to remove an electron. |
| Relationship | Enthalpy and ionization energy are indirectly related. | The ionization energy of an atom or ion is related to its electron affinity and electronegativity. |
| Effect of Enthalpy on Ionization Energy | Exothermic reactions release energy, resulting in more stable products with lower potential energy. These stable products require more energy to remove an electron, resulting in higher ionization energy. Endothermic reactions absorb energy, resulting in less stable products with a higher potential energy. These unstable products require less energy to remove an electron, resulting in lower ionization energy. | Enthalpy does not directly affect ionization energy, but it is indirectly related through the atom or ion's electron affinity and electronegativity. Higher electron affinity and electronegativity lead to a stronger attraction between the nucleus and electrons, resulting in higher ionization energy. |
| Examples | The combustion of methane (CH4) is an exothermic reaction that releases energy in the form of heat. The products of this reaction, carbon dioxide and water, are more stable than the reactant methane. Therefore, they require more energy to remove an electron, resulting in higher ionization energy. | The ionization energy of fluorine (F) is higher than that of chlorine (Cl), even though they are in the same group. This is because fluorine has a higher electron affinity and electronegativity, resulting in a stronger attraction between the nucleus and electrons and higher ionization energy. |
The ionization enthalpy of an element is dependent on its position in the periodic table. There is a general trend in the periodic table, whereby the ionization enthalpy increases from left to right across a period and decreases from top to bottom down a group. The increase in the ionization enthalpy across a period is due to the increase in the nuclear charge and the decrease in the atomic radius. The decrease in the ionization enthalpy down a group is due to the increase in the atomic radius and electron shielding.
Table 1: Trends in Ionization Enthalpy in the Periodic Table
| Period | Element | Ionization Enthalpy (kJ/mol) |
| 2 | Li | 520 |
| 2 | Be | 899 |
| 2 | B | 801 |
| 2 | C | 1086 |
| 2 | N | 1402 |
| 2 | O | 1314 |
| 2 | F | 1681 |
| 2 | Ne | 2081 |
Ionization enthalpy plays a vital role in various fields of science. In analytical chemistry, it is used to identify the presence of elements in a sample. The ionization energy of an element can be used to distinguish it from other elements in the sample. In addition, ionization enthalpy is used in the design of electronic devices such as transistors and diodes. It is also an essential parameter in studying chemical reactions and bonding.
Table 2: Ionization Enthalpy of Selected Elements
| Element | Ionization Enthalpy (kJ/mol) |
| Li | 520 |
| Na | 496 |
| K | 418 |
| Mg | 738 |
| Ca | 590 |
| Al | 578 |
| Si | 786 |
| P | 1012 |
| S | 1000 |
It takes more energy to remove an electron because the nuclear charge's pull on the topmost electron grows as the nuclear charge does. As a consequence, the energy of ionization increases.
As the atomic size increases, the negative electron's pull on the positive nucleus weakens, requiring less energy to eliminate one electron. As a consequence, the ionization energy decreases.
The outermost electron is protected from the nucleus' pull by the repelling effect of the interior electrons. The positive nucleus's attraction to the negative electron weakens with increasing shielding, needing less energy to extract an electron. As a consequence, the ionization energy decreases.
When moving down a group of elements, the ionization enthalpy decreases for the following reasons:
In order to measure ionization enthalpy, one must first understand what enthalpy is. Enthalpy is a measure of the heat content in a system. In order to calculate enthalpy, one must use the equation:
Enthalpy = Heat Capacity x Temperature
where heat capacity is the amount of heat required to raise the temperature of a substance by one degree Celsius. Once the heat capacity has been determined, the temperature can be plugged in and the enthalpy calculated.
Ionization enthalpy is the amount of heat required to remove an electron from an atom or molecule. This type of enthalpy is always positive, as it takes energy to remove an electron from a system. The equation for ionization enthalpy is:
Ionization Enthalpy = (Heat Capacity of Atom or Molecule) x (Temperature)
To calculate ionization enthalpy, one must determine the heat capacity of the atom or molecule in question. This can be done through experimentation or by using data from a reliable source. Once the heat capacity has been determined, the temperature can be plugged in, and the ionization enthalpy calculated.
Here are some key points to remember about "ionization enthalpy":
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By - Nikita Parmar 2023-08-25 09:48:44 , 11 min readIonization enthalpy is the amount of energy required to remove one mole of electrons from one mole of gaseous atoms or ions in their ground state.
The unit of ionization enthalpy is kilojoules per mole (kJ/mol) or electron volts (eV).
Ionization enthalpy increases across a period in the periodic table due to an increase in effective nuclear charge.
Ionization enthalpy decreases down a group in the periodic table due to an increase in atomic size and shielding effect.
Ionization enthalpy is a key factor in determining the reactivity of elements and is used to explain the properties and behavior of elements in various chemical reactions.
The factors affecting ionization enthalpy include the effective nuclear charge, atomic size, shielding effect, and the electron configuration of an atom.
The first ionization enthalpy is the energy required to remove the first electron from an atom, while the second ionization enthalpy is the energy required to remove the second electron from the same atom.
Energy is required in the process of ionization.
Beryllium has a higher first ionization energy compared to Boron due to its stable and complete electronic configuration of 1s22s2, which requires more energy to remove the first electron. In contrast, Boron has an electronic configuration of 1s22s23s1, which necessitates less energy to remove an electron than Beryllium.
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