Answer to Question #65973 in General Chemistry for Sarah Token

Question

define the term first ionisation energy and explain why this property generally increased across a period on the table of elements.

Answer 1

Definition (according to https://www.chemguide.co.uk/atoms/properties/ies.html):

The first ionisation energy is the energy required to remove one mole of the most loosely held electrons from one mole of gaseous atoms to produce 1 mole of gaseous ions each with a charge of 1+.

One of factors that affect the ionisation energy is the charge of the nucleus. The more protons are present in the nucleus, the more is the force of attraction between nucleus and electrons. As far as you know, the number of protons increases across the period, so does the energy of ionisation.