Aspects	Electron gain enthalpy	Electronegativity
Definition	Energy changes when an isolated gaseous atom gains an electron	Ability of an atom in a molecule to attract shared electrons towards itself
Unit	KJ/mol	No unit
Experimental determination	Element has a constant value that can be calculated experimentally.	Values cannot be determined experimentally
Role in bonding	Provides insights into an atom’s tendency to gain electrons, predict reactivity, and stability.	Influences the type of chemical bonding, particularly in covalent compounds
Trends	Increases across a period from left to right. Decreases down a group	Increases across a period from left to right. Decreases down a group

Classification Of Elements And Periodicity In Properties

Classifying elements and periodicity in properties is a crucial aspect of chemistry, organizing elements based on their characteristics and properties. Here is a detailed explanation of how this classification applies to metals, non-metals, metalloids, and noble gasses concerning electron gain enthalpy:

• Metals: Metals are elements that typically lose electrons to form positively charged ions (cations). They are known for properties like luster, malleability, ductility, and good conductivity of heat and electricity. Metals generally have low electron gain enthalpies due to their tendency to lose electrons rather than gain them.
• Non-Metals: Non-metals are elements that tend to gain electrons to form negatively charged ions (anions). Properties like brittleness, poor conductivity, and varied physical states at room temperature characterize them. Non-metals have higher electron gain enthalpies compared to metals as they have a greater tendency to gain electrons.
• Metalloids: Metalloids exhibit properties of both metals and nonmetals. They are found along the periodic table’s diagonal line between metals and nonmetals. Metalloids have intermediate electron gain enthalpies compared to metals and non-metals due to their mixed properties.
• Noble Gases: Noble gases are elements in Group 18 of the periodic table with stable electronic configurations. They have very high electron gain enthalpies as they have little tendency to gain or lose electrons, being inert or nonreactive.

Factors Affecting Electron Gain Enthalpy

The factors that affect electron gain enthalpy include:

Atomic Size

As the distance between the nucleus and the outermost shell increases, the tendency of the atom to gain electrons diminishes, leading to less negative electron gain enthalpy.

Effective Nuclear Charge

The effective nuclear charge increases from left to right in a period and decreases down a group, affecting the attraction of electrons from the outermost shell.

Electronic Configuration

Elements with fully or partially filled stable orbitals have a low tendency to gain electrons, resulting in low electron gain enthalpy. The electron gain enthalpy becomes more negative across periods and decreases down a group.

Variation of Electron Gain Enthalpy within a Group

The variation of electron gain enthalpy within a group can be explained as follows:

Down a Group: As we move down a group in the periodic table, the electron gain enthalpy becomes less negative. This trend is due to the simultaneous increase in atomic size and nuclear charge as we descend the group. However, the effect of the increase in atomic size is more significant than that of the nuclear charge. The attraction between the nucleus and the added electron decreases with the larger atomic size, leading to a less negative electron gain enthalpy.

Variation of Electron Gain Enthalpy along a Period

Across a Period: When moving from left to right across a period in the periodic table, the electron gain enthalpy becomes more negative. This trend occurs because the atomic size of elements decreases, and the effective nuclear charge increases as you progress from left to right. The increased nuclear charge enhances the force of attraction between the nucleus and the added electrons, leading to a more negative electron gain enthalpy.

Electron Gain Enthalpy of Fluorine is Less Negative than that of Chlorine

The electron gain enthalpy of fluorine is less negative than that of chlorine due to several factors:

• Atomic Size: Fluorine has a smaller atomic size compared to chlorine. The smaller size of fluorine results in stronger interelectronic repulsions in the 2p orbitals, making it less favorable for fluorine to gain an electron. It leads to a less negative electron gain enthalpy for fluorine.
• Attraction Outside the Shell: The smaller size of fluorine means there is less attraction outside the shell to gain an electron, contributing to its lower electron gain enthalpy compared to chlorine.
• Interelectronic Repulsions: In the case of fluorine, the added electron goes to the 2p-subshell, which is relatively small. This results in strong interelectronic repulsions in the small 2p-subshell, making it less favorable for fluorine to gain an electron compared to chlorine, where the added electron goes to the larger 3p-subshell.

Electron Gain Enthalpy of Noble Gases is Positive

The electron gain enthalpy of noble gasses is positive due to their stable electronic configuration. Noble gasses, such as helium, neon, argon, krypton, xenon, and radon, have a filled outer electron shell, making them highly stable and unreactive. Adding an extra electron to these stable atoms would disrupt their complete electron configuration, leading to high electronic repulsion and an unfavorable situation.

As a result, noble gasses resist the addition of electrons, requiring a large amount of energy to force an electron to bind to the stable atom. This resistance to accepting additional electrons results in noble gases’ positive electron gain enthalpy values. The positive electron gain enthalpy of noble gases reflects their inert nature and the energy needed to add an electron to an already stable configuration, making them unreactive and resistant to electron addition.

Also, Check

• Electron Affinity 
• Ionization Energy 
• What is Enthalpy

Electron Gain Enthalpy FAQs

What is electron gain enthalpy?

Electron gain enthalpy is the energy change that occurs when an isolated gaseous atom gains an electron to form a negative ion.

Why is electron gain reaction exothermic?

The electron gain reaction is exothermic because energy is released when an electron is added to an isolated gaseous atom, leading to a stable electronic configuration.

What factors affect electron gain enthalpy?

Factors like atomic size, nuclear charge, and electronic configuration influence the electron gain enthalpy of an element.

Which element has the highest electron gain enthalpy in the periodic table?

Chlorine has the highest electron gain enthalpy, with a value of -349 kJ/mol.

How does an electron gain enthalpy change across a period and down a group?

Electron gain enthalpy becomes more negative across a period from left to right due to increasing nuclear charge. It becomes less negative as you move down a group because of the increasing atomic size.