What is Electron Gain Enthalpy of Elements?
To define electron gain enthalpy, sometimes, it is also called Electron affinity, although there exists a small difference between them. The amount of energy released when an electron is added to an isolated gaseous atom is characterised as an electron gain enthalpy. During the addition of the electron, either the energy can be released or absorbed.
Explanation of Electron Gain Enthalpy
Let us consider two metals, Sodium and Magnesium. Metals will lose electrons to obtain the inert gas configuration. Thus, both Magnesium and Sodium atoms will not add electrons easily. Some external energy is required to add the electron to their atoms. Therefore, electron gain enthalpy for metals will be given as positive. Since the Magnesium atom is small, the attractive nuclear force will be more on the electrons, whereas the size of the Sodium atom is comparatively larger than that of the Magnesium atom. Therefore, the nuclear force applied to the electrons in the case of Sodium will be given as less.
Electron Gain Enthalpy
So, we will apply the energy in both cases, but the amount of energy required in the case of Magnesium will be lesser compared to Sodium because of the help we are receiving from the nuclear charge of Magnesium in electron attraction. So, the electron gain enthalpy in both cases will result in positive, but the atom having a smaller size will contain lesser positive electron gain enthalpy. By this, we can conclude that electron gain enthalpy completely depends on the nuclear charge and atomic radius.
Now, let us take two non-metals, Chlorine and Sulphur. The electronic configuration of the Chlorine is given as 3p5 and Sulphur contains the configuration of 3p4. If we add a single electron to these non-metals, then Chlorine will accept it first. After acquiring a single electron, it will achieve its noble gas configuration. After acquiring a single electron, the stability of Chlorine will result in more.
Hence, it will remove the maximum amount of energy. Therefore, the electron gain enthalpy of the chlorine compound is more negative as compared to the Sulphur. Let us verify this by the nuclear charge and property of atomic radius size. The atomic radius of chlorine is smaller compared to the Sulphur. So, the effective nuclear charge on an electron in the chlorine case will be more compared to Sulphur. Therefore, chlorine contains more negative electron gain enthalpy.
From this discussion, we can understand that electron gain enthalpy completely depends on three factors given below:
Electronic configuration
Atomic radius
Nuclear charge.
Electron affinity is meant as love for electrons and the negative of the electron gain enthalpy. By using the thermodynamic concept, we can find a relationship between electron gain enthalpy and electron affinity. It means,
Electron gain enthalpy = Electron affinity - (5/2)RT
Where T is given as the temperature on the Kelvin scale and R is given as the universal gas constant.
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. Similar to it, we can also define the electron gain enthalpy of nitrogen.
Factors Affecting Electron Gain Enthalpy
Atomic Size
The distance between the nucleus and the final shell that accepts incoming electrons grows as the atom's size grows. This will decrease the force of attraction between the nucleus and the incoming electron. Thus, the electron gain enthalpy results in less negative.
Nuclear Charge
As the nuclear charge increases, the force of attraction between the incoming electron and nucleus increases, which is the highest electron gain enthalpy. Therefore, the enthalpy becomes more negative.
Electronic Configuration
Elements with exactly either half-filled or completely filled orbitals are very stable. You have to supply the energy to add an electron. As a result, their electron gain enthalpy is quite positive. The electron gain enthalpy becomes less negative while going from top to bottom in a group. At the same time, it becomes more negative in going from left to right in a period.
Electron Gain Enthalpy Variation within the Group
The electron gain enthalpy results in less negative as we move down a group.
Also, as we move down a group, both the nuclear charge and atomic size increase, but the effect of an increase in the atomic size is more pronounced compared to the nuclear charge.
With the increase in atomic size, the nucleus’ attraction for the incoming electron decreases. Therefore, the electron gain enthalpy results in less negative.
Chlorine holds the most negative electron gain enthalpy.
Variation along a Period
Electron gain enthalpy becomes more negative, moving from left to right in a period.
As we move across the period from the left to the right direction, the nuclear charge increases and the atomic size decreases. These two factors tend to increase the attraction by the nucleus for the incoming electron. Thus, electron gain enthalpy results in more negative in a period when travelling from left to right.
Halogens (electron gain enthalpy of halogens) contain the most negative electron gain enthalpy. As we move from the direction of chlorine to iodine, the electron gain enthalpies become very negative due to the corresponding increase in their atomic radii.
The force that attracts the extra electron diminishes as the distance between the nucleus and the subshell that receives it grows, and therefore the electron gain enthalpy becomes less negative as we travel down the group from - Cl → Br → I.
Fluorine has a Lower Negative Electron Gain Enthalpy than Chlorine
This is because of its small size. The electron-electron repulsion in the relatively compact to the 2p subshell is comparably strong due to its tiny size. Thus, the incoming electron is not accepted with similar ease as is the chlorine case.
Electron Gain Enthalpy of the Nobel Gases is Positive
The atoms of these elements contain a completely filled subshell. As a result, there exists no room in their valence orbitals and the additional electron should be placed in an orbital of the next higher shell. Resultantly, energy has to be supplied to add on the additional electrons.
Some Facts About Electron Gain Enthalpy
Energy is released at the time when the electron is added to the atom. Thus, the electron gain enthalpy results in negative.
The electron gain enthalpy of halogens is extremely negative because they can accept the additional electron and get the closest stable noble gas configuration.
Noble gases contain large positive electron gain enthalpy. This is because the additional/extra electron is placed in the next higher principal quantum energy levels. Therefore, a highly unstable electronic configuration production takes place.
Electron Gain Enthalpy Trends Along a Periodic Table
The amount of energy released when an isolated gaseous atom takes an electron to create a monovalent gaseous anion is known as electron gain enthalpy. If an atom contains a spontaneous tendency, it means a positive tendency to gain an electron, then conventionally, its electron gain enthalpy is said to be negative. Whereas, if the atom is reluctant to gain an electron, it means it has a negative tendency to gain the electron and is forced to accept it; its electron gain enthalpy is said to be positive.
In general, when the atomic number increases over time, the electron gain enthalpy becomes more negative. The effective nuclear charge increases and atomic size decreases as we go from the left to right direction across a period and consequently, it will be easier to add an electron to the smaller atom since the added electron on average would be closer to the positively charged nucleus.
The electron gain enthalpy trends that occur in electron gain enthalpy values within a period are irregular for elements of groups 2, 15 and 18 since they have atoms having symmetrical configuration (having half-filled and filled orbitals in the same subshell) and thus do not have any urge to take up the extra electrons because their configuration will become either less stable or unsymmetrical.
Difference Between Electron Gain Enthalpy and Electronegativity
Let us look at the difference between electron affinity and electron gain enthalpy in detail.
The primary difference between electron gain enthalpy and electronegativity is that the Electron Gain Enthalpy vs. Electronegativity.
An electron is defined as a subatomic particle of an atom. Electrons can be found everywhere because every matter is made up of atoms. However, these electrons are essential in a few chemical reactions since the exchange of electrons is the only difference between products and reactants in these reactions.
Electronegativity and electron gain enthalpy are the two chemical terms that are used to explain the binding of an electron with an atom. Electron gain enthalpy is given as the amount of energy released by the atom when an electron is gained from outside. Electronegativity is defined as the ability of an atom to gain electrons from outside. Thus, an electron gain enthalpy quantifies electronegativity. The primary difference between electronegativity and electron gain enthalpy is that electron gain enthalpy is measured in kJ/mol units, whereas electronegativity is unitless and measured by the Pauling scale.
Conclusion
The energy produced when a neutral isolated gaseous atom receives an extra electron to form the gaseous negative Ion, or anion, is called electron gain enthalpy. Heg can be used to represent it. The bigger the quantity of energy released in the aforementioned process, the higher the element's electron gain enthalpy.
The strength or firmness with which an additional electron is attached to an element is measured by its electron gain enthalpy. It's measured in kJ per mole or electron volts per atom. When an electron is added to an atom, the process can be either endothermic or exothermic.
FAQs on Electron Gain Enthalpy of Elements
1. Explain electron gain enthalpy in detail.
Electron gain enthalpy of the element is defined as the energy released when a neutral isolated gaseous atom accepts an extra electron to form the gaseous negative Ion, which means the anion. We can denote it by Δ, and H is an example of it. The greater the amount of energy released in the above process, the higher is the element’s electron gain enthalpy.
The electron gain enthalpy of an element is given as a measure of the strength or firmness with which an extra electron is bound to it. It is measured either in the units kJ per mole of electron volts per atom. It can be either an exothermic or endothermic reaction when you add an electron to the atom.
2. Differentiate between electron affinity and electron gain enthalpy.
Electron gain enthalpy is defined as the energy released when an isolated gaseous atom accepts the electron to convert into an anion.
Now, whenever the energy is released from the system to the surroundings, it is taken to be negative (as per thermodynamics) and positive when the system absorbs energy; thus, electrons gain enthalpy, in general, taken as negative. But in the case of noble gases, an electron has to be placed in the adjacent shell leading to instability, so the electron gain enthalpy is given as positive there.
Also remember that, when an atom turns from a stable to an unstable state, electron gain enthalpy results in positive while when it turns from an unstable to a stable state, then electron gain enthalpy results in negative.
Basically, an Electron Affinity is the same thing, but it contains the reverse sign as that of the electron gain enthalpy.
3. What is Positive electron gain enthalpy?
It exhibits that the atom is reluctant for the addition of a new electron in its valence shell and this addition of an electron is driving it towards instability. For this addition of an electron, energy required to be spent making the positive. Let us take an example of noble gases that contain large positive electron gain enthalpies because the added electron should enter the next higher principal quantum level leading to an unstable electronic configuration.
In general, the electron gain enthalpy becomes more negative in going from left to right in a period, while it becomes less negative going from top to bottom in a group. With a few exceptions, the variance in electron gain enthalpies does not follow a completely regular pattern over time or between groups.
4. Why is the energy released in an electron gain enthalpy?
The rule is as follows: if the sum of the products in a chemical reaction is less than the reactants before the reaction, then the overall reaction is- (-enthalpy) and is generally exothermic. An example is the Reduction of Iron oxide with Aluminium, to produce iron- (thermit process) solid to liquid phase and lots of heat - 2500℃.
If the products’ sum is greater than the weight of reactants before the reaction, the overall reaction is enthalpy and considered endothermic.
An Example is anhydrous/hydration urea or ammonium nitrate, which is used in freeze packs for soothing bruises. (from Solid to liquid phase) very cold –5-8℃.
