Define the term 'first ionisation energy' and explain why the first ionisation energy shows a general increase across period 2

The first ionisation energy is the energy required to remove an electron from each atom in one mole of gaseous atoms to produce +1 charged gaseous ions.The first ionisation energy shows an general increase across period 2 at the number of shells stay the same but the nuclear charge increases. Therefore electrons experience a greater attraction to the nucleus as the shielding remains the same