What is the difference between electron gain enthalpy and electron affinity?

Electron gain enthalpy ($\Delta_{eg}H$) is the enthalpy change when an electron is added to a neutral gaseous atom to form a gaseous anion. It can be positive (endothermic) or negative (exothermic). Electron affinity (EA) is defined as the energy released when an electron is added to a neutral gaseous atom. Therefore, if the process is exothermic (energy released), EA = -$\Delta_{eg}H$. If the process is endothermic (energy absorbed), EA is not typically defined as a positive value, or it's considered zero/negative. For NEET, it's safer to stick to electron gain enthalpy and its sign convention.

Why is the electron gain enthalpy of fluorine less negative than that of chlorine?

This is a significant anomaly. Despite fluorine being smaller and having a higher effective nuclear charge than chlorine, its electron gain enthalpy is less negative. This is because fluorine's 2p subshell is very compact. When an incoming electron approaches, it experiences strong inter-electronic repulsion from the already existing electrons in the small 2p orbitals. This repulsion makes the electron addition less favorable (less exothermic) compared to chlorine, where the incoming electron enters the larger 3p subshell, experiencing less repulsion.

Why are the electron gain enthalpies of noble gases positive?

Noble gases (Group 18) possess completely filled valence electron shells, giving them extremely stable electronic configurations. Adding an extra electron to such a stable configuration would require it to enter a new, higher energy shell, which is energetically unfavorable. This disruption of stability and the need to overcome strong electron-electron repulsion means energy must be supplied to force an electron onto a noble gas atom, resulting in a positive electron gain enthalpy.

What is the effect of hybridization on electronegativity?

The electronegativity of an atom increases with increasing 's' character in its hybrid orbitals. This is because 's' orbitals are spherical and closer to the nucleus than 'p' orbitals. Therefore, electrons in hybrid orbitals with more 's' character are held more tightly by the nucleus. For example, carbon in an sp hybridized state (50% s character) is more electronegative than in an $sp^2$ state (33.3% s character), which is more electronegative than in an $sp^3$ state (25% s character). This explains why acetylenic hydrogens are more acidic than ethylenic or alkyl hydrogens.

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Electron Gain Enthalpy and Electronegativity

Q: How does electronegativity differ from electron gain enthalpy?

Electron gain enthalpy is an absolute energy value measured for an isolated gaseous atom, quantifying its tendency to *accept* an electron to form an anion. Electronegativity, conversely, is a relative measure of an atom's ability to *attract shared electrons* towards itself within a chemical bond. EGE is about gaining an electron entirely, while EN is about pulling shared electrons closer. EGE has units (kJ/mol), while EN is a dimensionless relative scale.

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Electron gain enthalpy is defined as the enthalpy change that occurs when an electron is added to a neutral gaseous atom to form a gaseous anion. It is a measure of the ease with which an atom accepts an electron. A more negative (or less positive) electron gain enthalpy indicates a greater tendency for the atom to accept an electron. Electronegativity, on the other hand, is a qualitative measure …

Quick Summary

Electron gain enthalpy ( $\Delta_{eg}H$ ) is the energy change when an electron is added to a neutral gaseous atom. A negative value indicates energy release (exothermic), signifying a strong attraction for the electron, while a positive value indicates energy absorption (endothermic), meaning the atom resists electron addition.

Factors influencing EGE include effective nuclear charge (higher $Z_{eff}$ means more negative EGE), atomic size (larger size means less negative EGE), and electronic configuration (stable configurations like noble gases or half-filled orbitals lead to positive EGE).

EGE generally becomes more negative across a period and less negative down a group, with notable exceptions like fluorine having a less negative EGE than chlorine due to electron-electron repulsion in its small 2p subshell.

The second electron gain enthalpy is always positive due to repulsion.

Electronegativity (EN) is a relative measure of an atom's ability to attract shared electrons in a chemical bond. It increases across a period and decreases down a group, mirroring the trends of effective nuclear charge and atomic size.

Factors like hybridization (more 's' character increases EN) and oxidation state (higher positive oxidation state increases EN) also play a role. Electronegativity differences determine bond polarity and character.

While both properties relate to electron attraction, EGE is an absolute energy value for isolated atoms, whereas EN is a relative measure within a bond.

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Key Concepts

Trends in Electron Gain Enthalpy

Electron gain enthalpy generally becomes more negative across a period due to increasing effective nuclear…

Factors Influencing Electronegativity

Electronegativity is primarily influenced by effective nuclear charge and atomic size. Higher effective…

Relationship between EGE, EN, and Stability

A highly negative electron gain enthalpy indicates that an atom readily accepts an electron to form a stable…

Electron Gain Enthalpy ($\Delta_{eg}H$): — Energy change when

e^-

added to

X(g) \rightarrow X^-(g)

- Negative: Exothermic (energy released), favorable. - Positive: Endothermic (energy absorbed), unfavorable. - Trends: Generally more negative across period, less negative down group. - Exceptions: F < Cl (less negative EGE for F), Noble gases, Be, Mg, N, P have positive EGE. - Successive EGE: $\Delta_{eg}H_2$ always positive due to repulsion.

Electronegativity (EN): — Ability of atom to attract shared

e^-

in a bond.

- Relative scale (Pauling: F=4.0). - Trends: Increases across period, decreases down group. - Factors: $Z_{eff}$ (increases EN), Atomic size (decreases EN), Hybridization (more 's' character, increases EN), Oxidation state (higher positive, increases EN). - Application: $\Delta EN$ determines bond polarity.

EGE: Electron Gain Exceptionalities: For Noble Beasts, Many Odd Signs. (F for Fluorine anomaly, N for Nitrogen, Noble for Noble gases, Be for Beryllium, Mg for Magnesium, O for Oxygen anomaly, S for Sulfur anomaly - all have less negative or positive EGEs than expected/their group members below them).

EN: For Our Neighbor Carbon, Bond Is Stronger. (Order of EN: F > O > N > C > B > I > S - helps recall top electronegative elements and their relative order).

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