Why does ionization energy increase across a period?

First of all, let's define ionization energy. Ionization energy is the energy needed to remove 1 electron from each atom in 1 mole of gaseous atoms. The higher this energy is, the harder it is to remove the electron. The first main factor that determines ionization energy is nuclear charge (this is the relative charge in the nucleus of the atom and increases as the number of protons increases). As nuclear charge increases, Ionization energy increases. This is because the electrons are held more strongly to the nucleus by electrostatic forces of attraction between the positive nucleus and the negative electrons. Another factor effecting ionization energy is shielding, this is where electrons in orbitals closer to the nucleus 'shield' the valence electrons so they feel a smaller attraction from the nucleus, making them easier to remove. Across a period there is no significant change so this factor is not important. The third factor is the distance of the valence electron from the nucleus, as the distance increases, the ionization energy decreases, as the electrons feel the electrostatic forces less. Again, across a period there is no significant change in distance and so this factor isn't important. Although the last two factors don't effect ionization energy significantly across the period, they are still important to mention in your answer!

AF
Answered by Amelia F. Chemistry tutor

27960 Views

See similar Chemistry A Level tutors

Related Chemistry A Level answers

All answers ▸

State the trend in electronegativity for the elements of group 17 and explain why this trend occurs.


You have 3.51g of hydrated zinc sulphate. You heat up the zinc sulphate until all the water has evaporated from it. The weight after heating is 1.97g. Find how many H2O molecules per zinc sulphate molecule there are in the hydrated form of it.


In terms of reaction mechanisms, what exactly is the rate-determining step?


Heating 3.210g of hydrated magnesium sulfate, MgSO4.XH2O, forms 1.567g of anhydrous magnesium sulfate. Find the value of X and write the formula of the hydrated salt


We're here to help

contact us iconContact ustelephone icon+44 (0) 203 773 6020
Facebook logoInstagram logoLinkedIn logo

MyTutor is part of the IXL family of brands:

© 2025 by IXL Learning