MYTUTOR SUBJECT ANSWERS

172 views

Explain the trend in Ionisation energy when moving across a period and down a group

Key definitions/explanation of terms

Ionisation energy is the energy required to remove one mole of electrons from one mole of gaseous atoms to produce one mole of gaseous ions with a 1+ charge.

Electron shielding

Electrons carry a 1- charge and are located very close to one another in the atom. As a result of this the electrons repel one another. This effect is referred to as electron shielding. The more subshells populated in the atom the greater this shielding effect is.

Answer

The energy required to remove one valence electron from the outer shell is dependent upon the force the electron experiences due to the nucleus- this is called the effective nuclear charge.

This contributes to the ionisation energy measured as the larger the atomic radius, the further from the nucleus the valence electron is (therefore less "of a pull" experienced) so the less energy required to remove it.  

When moving from left to right across a period the ionisation energy generally increases. This may seem counterintuitive to some but can easily be explained. Each successive element gains an extra proton and electron. The result of this is the size of the nucleus increases whilst the same number of subshells are being populated. As a result the valence electrons experience a greater pull from the nucleus meaning they are drawn in closer. Subsequently the atomic radius decreases and the ionisation energy increases. 

A similar thought process can be applied when descending a group. Each successive element in the group populates the next set of subshells whilst simultaneously gaining protons. However, as more electrons are added the valence electrons experience a greater electron shielding from the inner subshells. Consequently, the valence electrons move further from the nucleus and less energy is required for the removal of one electron.

This can be demonstrated using the reaction of the alkali metals with water- a typical experiment which many students have witnessed. As the group is descended the reactions become more vigorous in nature. One contributing factor to this is the decreasing ionisation energy of group 1. It becomes easier to remove the valence electron as you move down the group making the element more reactive so the reaction proceeds in a quicker time frame. 

Olivia F. GCSE Chemistry tutor, A Level Chemistry tutor, Mentoring -P...

8 months ago

Answered by Olivia, an A Level Chemistry tutor with MyTutor

Still stuck? Get one-to-one help from a personally interviewed subject specialist

80 SUBJECT SPECIALISTS

£26 /hr

Lorenzo C.

Degree: Biomedical Sciences with Honours in Infectious Diseases (Bachelors) - Edinburgh University

Subjects offered: Chemistry, Physics+ 1 more

Chemistry
Physics
Biology

“Hey! I'm Lorenzo and I study Biomedical Sciences with an honours in Infectious Diseases at the University of Edinburgh. I'd be happy to help you with Biology, Chemistry and Physics at GCSE or at A-Level.  I have previous experience tu...”

£20 /hr

Oliver P.

Degree: Biology (Masters) - Bristol University

Subjects offered: Chemistry, Science+ 5 more

Chemistry
Science
Maths
Human Biology
Further Mathematics
Extended Project Qualification

“The tutor: I am a Biology MSci student at Bristol University and have a deep curiosity and passion for multiple fields of science and technology. I am patient and have a lot of experience teaching children in the age range of 11-...”

£26 /hr

Osama H.

Degree: Medicine (MBBS/BSc) (Bachelors) - Imperial College London University

Subjects offered: Chemistry, Geography+ 4 more

Chemistry
Geography
Biology
.UKCAT.
.BMAT (BioMedical Admissions)
-Personal Statements-

“Hi I'm Osama, a medical student at Imperial College London. I'm happy to help with core subjects at GCSE, and Biology and Chemistry and A-level. I am also happy to help you get that coveted place at medical school!”

About the author

£20 /hr

Olivia F.

Degree: Chemistry (Masters) - Nottingham University

Subjects offered: Chemistry, -Personal Statements-

Chemistry
-Personal Statements-

“A bit about me:Hi I'm Olivia, a penultimate year Chemistry MSci student at The University of Nottingham! Throughout my time in education I have always had a passion for all things science, especiallyChemistry and Physics.I pride my...”

MyTutor guarantee

You may also like...

Other A Level Chemistry questions

What is Effective Nuclear Charge?

How do mass spectrometers work?

Why are transition metal complexes coloured?

View A Level Chemistry tutors

Cookies:

We use cookies to improve our service. By continuing to use this website, we'll assume that you're OK with this. Dismiss

mtw:mercury1:status:ok