Electron Gain Enthalpy
Describes the energy change when an electron is added to a neutral gaseous atom, including its sign conventions and periodic trends.
What is Electron Gain Enthalpy?
The energy change that accompanies the addition of an electron to a neutral gaseous atom to form a negative ion.
Key formula / rule: Electron Gain Enthalpy
Key points
- Define electron gain enthalpy.
- Explain the sign convention associated with electron gain enthalpy.
- Describe the periodic trends of electron gain enthalpy across periods and down groups.
- Identify elements with highly negative or positive electron gain enthalpies.
Common exam trap
Confusing electron gain enthalpy with electronegativity.
Definitions
- Term
Electron Gain Enthalpy (ΔHeg)
- Meaning
The energy change that accompanies the addition of an electron to a neutral gaseous atom to form a negative ion.
- Term
Exothermic Process
- Meaning
A process that releases energy into the surroundings. For electron gain enthalpy, this corresponds to a negative value.
- Term
Endothermic Process
- Meaning
A process that absorbs energy from the surroundings. For electron gain enthalpy, this corresponds to a positive value.
Learning objectives
Define electron gain enthalpy.
Explain the sign convention associated with electron gain enthalpy.
Describe the periodic trends of electron gain enthalpy across periods and down groups.
Identify elements with highly negative or positive electron gain enthalpies.
Differentiate between first and subsequent electron gain enthalpies.
Formulae
- Name
Electron Gain Enthalpy
- Note
Represents the energy change when an electron is added to a neutral gaseous atom.
- Expression
X(g) + e⁻ → X⁻(g) ΔHeg
Prerequisites
Atomic structure
Electronic configuration
Periodic classification of elements
Concept of ions (cations and anions)
Energy changes in chemical processes (exothermic and endothermic)
Common mistakes
Confusing electron gain enthalpy with electronegativity.
Not considering the sign convention (negative for release, positive for absorption).
Assuming all elements have negative electron gain enthalpies.
Forgetting that second and subsequent electron gain enthalpies are always endothermic.
Incorrectly applying periodic trends without considering exceptions.
Keywords
Electron Gain Enthalpy
Enthalpy Change
Exothermic
Endothermic
Anion Formation
Periodic Trends
Noble Gases
Halogens
Alkaline Earth Metals
Practice preview
The electron gain enthalpy of an element X is -328 kJ/mol. What does this value indicate?…
easy
Why does the electron gain enthalpy of Fluorine (F) become less negative than that of Chlorine (Cl)?…
medium
Consider the following electron gain enthalpies (in kJ/mol):…
hard