Question

Why do scientists use atoms in the gas phase to measure ionization energies and electron affinities

Answer 1

Because they use high temperature to ionize the element. Temperatures mostly ionize if not all elements exist as a gas. 

Answer 2

Answer:

At the gaseous phase the intermolecular force of attraction between atoms becomes far apart. The atoms can easily be added up with an electron or electrons can be removed from an atom.

Higher energy is required in this process.

Explanation:

Why do scientists use atoms in the gas phase to measure ionization energies and electron affinities

Electron Affinity is where there is a change in energy when  electron is added to atom in its gaseous phase. The atom becomes negatively charged.

Ionization Energy is defined as the energy required to remove an electron from gaseous atom.

At the gaseous phase the intermolecular force of attraction between atoms becomes far apart. The atoms can easily be added up with an electron or electrons can be removed from an atom.