The first ionisation energy is the energy required to

  • A. add one electron to a gaseous atom
  • B. remove one mole of electrons from one mole of gaseous atoms, forming gaseous unipositive ions
  • C. break one mole of covalent bonds
  • D. convert one mole of a solid into a gas

Explanation

The definition specifies the gaseous state so that no lattice or intermolecular forces interfere, and it is always endothermic because an electron must be pulled away from an attracting nucleus. Adding an electron to a gaseous atom is electron affinity, the reverse process. Second ionisation energy is always larger than the first, since the electron is being removed from a positively charged ion.

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