Differentiate between electron affinity and
electronegativity. Why are the electron
affinities of noble gases zero ?
Answers
Answer:
Electron affinity is a property of an isolated atom in the gaseous state. It is an energy term and is measured in units of joules per mole.
Electronegativity is a property of an atom in a molecule. It can be expressed only in arbitrary dimensionless units with respect to a reference atom.
Electron Affinity
Electron affinity, EA, measures the energy released when an electron adds to a gaseous atom.
It is usually reported as the energy per mole of atoms. For example,
Cl(g) + e⁻ → Cl⁻(g); EA = -349 kJ/mol
Electronegativity
Electronegativity,
χ
, is the tendency of an atom to attract toward itself the electron density in a shared bond.
Electronegativity cannot be directly measured. It must be calculated from other properties such as bond energies, ionization energies, and electron affinities of the bonded atoms.
This gives a dimensionless quantity on a relative "Pauling scale" that runs from around 0.7 to 3.98. Hydrogen is assigned an arbitrary value of 2.20 "Pauling units".
The greater the electronegativity difference
Δ
E
N
between the two atoms, the more the electron density will be pulled toward the more electronegative atom.
The less electronegative atom will have a decreased electron density.
The protons attached to that atom will be deshielded.
As the electronegativity of the substituent increases, so does the extent of deshielding, and so does the chemical shift.
Answer:
:Electron gain enthalpy
Tendency to gain electrons for an isolated gaseous atom is its electron gain enthalpy.
Electronegativity
Tendency to attract the shared pairs of electrons for an atom which is in chemical compound is its electronegativity.