Question

what is ionisation enthalpy​

Answer 1

Answer:

Cations are formed via ionisation energy; this is the process by which atoms lose electrons to form cations.

The first ionisation energy is the energy required to remove the outermost electron from each atom in one mole of a gaseous substance, to form one mole of gaseous +1 ions under standard conditions. This is an endothermic reaction as energy is absorbed/required in order to remove the outer electron from an atom as the electron needs to go from having a lower intrinsic energy (when in the orbital of the atom, attracted to the positively charged nucleus) to a higher intrinsic energy (when it is removed from the atom, thus further away from the positively charged nucleus at a higher energy level in the environment). This means that the value for the enthalpy change in first ionisation energy in KJMol-1 will be positive.

The cation formed will have a smaller atomic radius as the outermost electron is closer to the nucleus at a lower energy level, thus it has a lower intrinsic energy and is harder to remove (as there are stronger electrostatic forces of attraction between the outer electron and the positively charged nucleus). This means that the resultant ion has a smaller electron cloud.

Anions are formed via electron affinity; this is the process by which atoms gain electrons to form anions.

This process is known as the first electron affinity, which is the energy released when each atom in one mole of gaseous atoms gains an electron (which is added to the outermost orbital) to form one mole of gaseous -1 ions under standard conditions. This is an exothermic process as energy is released, thus the value for the enthalpy change in KJMol-1 is negative. Because this reaction is exothermic, it is energetically favourable therefore the anion formed is more stable, as it has a full outer shell. This also means that the outermost electron (gained during the formation of the anion in first electron affinity) is further away from the nucleus at a higher energy level (thus it has a higher intrinsic energy and is easier to remove as there are less electrostatic forces of attraction between it and the positively charged nucleus). This means that the anion has a larger atomic radius, as the size of the electron cloud is larger