<< Chapter < Page Chapter >> Page >

Ionisation energy

Ionisation energy is the energy that is needed to remove one electron from an atom. The ionisation energy will be different for different atoms.

The second ionisation energy is the energy that is needed to remove a second electron from an atom, and so on. As an energy level becomes more full, it becomes more and more difficult to remove an electron and the ionisation energy increases . On the Periodic Table of the Elements, a group is a vertical column of the elements, and a period is a horizontal row. In the periodic table, ionisation energy increases across a period, but decreases as you move down a group. The lower the ionisation energy, the more reactive the element will be because there is a greater chance of electrons being involved in chemical reactions. We will look at this in more detail in the next section.

Refer to the data table below which gives the ionisation energy (in kJ · mol - 1 ) and atomic number (Z) for a number of elements in the periodic table:

Z Ionisation energy Z Ionisation energy
1 1310 10 2072
2 2360 11 494
3 517 12 734
4 895 13 575
5 797 14 783
6 1087 15 1051
7 1397 16 994
8 1307 17 1250
9 1673 18 1540
  1. Draw a line graph to show the relationship between atomic number (on the x-axis) and ionisation energy (y-axis).
  2. Describe any trends that you observe.
  3. Explain why...
    1. the ionisation energy for Z = 2 is higher than for Z = 1
    2. the ionisation energy for Z = 3 is lower than for Z = 2
    3. the ionisation energy increases between Z = 5 and Z = 7

Khan academy video on periodic table - 2

By now you should have an appreciation of what the periodic table can tell us. The periodic table does not just list the elements, but tells chemists what the properties of elements are, how the elements will combine and many other useful facts. The periodic table is truly an amazing resource. Into one simple table, chemists have packed so many facts and data that can easily be seen with a glance. The periodic table is a crucial part of chemistry and you should never go to science class without it.

The following presentation provides a summary of the periodic table


  • Elements are arranged in periods and groups on the periodic table. The elements are arranged according to increasing atomic number.
  • A group is a column on the periodic table containing elements with similar properties. A period is a row on the periodic table.
  • The groups on the periodic table are labeled from 1 to 8. The first group is known as the alkali metals, the second group is known as the alkali earth metals, the seventh group is known as the halogens and the eighth group is known as the noble gases. Each group has the same properties.
  • Several trends such as ionisation energy and atomic diameter can be seen across the periods of the periodic table
  • An ion is a charged atom. A cation is a positively charged ion and an anion is a negatively charged ion.
  • When forming an ion, an atom will lose or gain the number of electrons that will make its valence energy level full.
  • An element's ionisation energy is the energy that is needed to remove one electron from an atom.
  • Ionisation energy increases across a period in the periodic table.
  • Ionisation energy decreases down a group in the periodic table.

End of chapter exercises

  1. For the following questions state whether they are true or false. If they are false, correct the statement.
    1. The group 1 elements are sometimes known as the alkali earth metals.
    2. The group 2 elements tend to lose 2 electrons to form cations.
    3. The group 8 elements are known as the noble gases.
    4. Group 7 elements are very unreactive.
    5. The transition elements are found between groups 3 and 4.
  2. Give one word or term for each of the following:
    1. A positive ion
    2. The energy that is needed to remove one electron from an atom
    3. A horizontal row on the periodic table
    4. A very reactive group of elements that is missing just one electron from their outer shells.
  3. For each of the following elements give the ion that will be formed:
    1. sodium
    2. bromine
    3. magnesium
    4. oxygen
    Click here for the solution
  4. The following table shows the first ionisation energies for the elements of period 1 and 2.
    Period Element First ionisation energy ( kJ . mol - 1 )
    1 H 1312
    He 2372
    Li 520
    Be 899
    B 801
    C 1086
    2 N 1402
    O 1314
    F 1681
    Ne 2081
    1. What is the meaning of the term first ionisation energy ?
    2. Identify the pattern of first ionisation energies in a period.
    3. Which TWO elements exert the strongest attractive forces on their electrons? Use the data in the table to give a reason for your answer.
    4. Draw Aufbau diagrams for the TWO elements you listed in the previous question and explain why these elements are so stable.
    5. It is safer to use helium gas than hydrogen gas in balloons. Which property of helium makes it a safer option?
    6. 'Group 1 elements readily form positive ions'. Is this statement correct? Explain your answer by referring to the table.

Questions & Answers

so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
how to fabricate graphene ink ?
for screen printed electrodes ?
What is lattice structure?
s. Reply
of graphene you mean?
or in general
in general
Graphene has a hexagonal structure
what is biological synthesis of nanoparticles
Sanket Reply
what's the easiest and fastest way to the synthesize AgNP?
Damian Reply
types of nano material
abeetha Reply
I start with an easy one. carbon nanotubes woven into a long filament like a string
many many of nanotubes
what is the k.e before it land
what is the function of carbon nanotubes?
I'm interested in nanotube
what is nanomaterials​ and their applications of sensors.
Ramkumar Reply
what is nano technology
Sravani Reply
what is system testing?
preparation of nanomaterial
Victor Reply
Yes, Nanotechnology has a very fast field of applications and their is always something new to do with it...
Himanshu Reply
good afternoon madam
what is system testing
what is the application of nanotechnology?
In this morden time nanotechnology used in many field . 1-Electronics-manufacturad IC ,RAM,MRAM,solar panel etc 2-Helth and Medical-Nanomedicine,Drug Dilivery for cancer treatment etc 3- Atomobile -MEMS, Coating on car etc. and may other field for details you can check at Google
anybody can imagine what will be happen after 100 years from now in nano tech world
after 100 year this will be not nanotechnology maybe this technology name will be change . maybe aftet 100 year . we work on electron lable practically about its properties and behaviour by the different instruments
name doesn't matter , whatever it will be change... I'm taking about effect on circumstances of the microscopic world
how hard could it be to apply nanotechnology against viral infections such HIV or Ebola?
silver nanoparticles could handle the job?
not now but maybe in future only AgNP maybe any other nanomaterials
I'm interested in Nanotube
this technology will not going on for the long time , so I'm thinking about femtotechnology 10^-15
can nanotechnology change the direction of the face of the world
Prasenjit Reply
At high concentrations (>0.01 M), the relation between absorptivity coefficient and absorbance is no longer linear. This is due to the electrostatic interactions between the quantum dots in close proximity. If the concentration of the solution is high, another effect that is seen is the scattering of light from the large number of quantum dots. This assumption only works at low concentrations of the analyte. Presence of stray light.
Ali Reply
the Beer law works very well for dilute solutions but fails for very high concentrations. why?
bamidele Reply
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
Privacy Information Security Software Version 1.1a
What makes metals better to use as wires than non-metals? (please link to bonding type)??? HELP
Yash Reply

Get the best Algebra and trigonometry course in your pocket!

Source:  OpenStax, Chemistry grade 10 [caps]. OpenStax CNX. Jun 13, 2011 Download for free at http://cnx.org/content/col11303/1.4
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Chemistry grade 10 [caps]' conversation and receive update notifications?