periodicity Flashcards
What is periodicity and give some examples of periodicity properties.
Periodicity refers to repeating trends in properties of elements, for example ionisation energy, melting point and structure.
What is the definition for the first ionisation energy?
The first ionisation energy is the energy required to remove one electron from each atom in one mol of gaseous atoms of an element to form one mol of gaseous 1+ ions.
Write the first ionisation energy equation for Na.
Na(g) -> Na+ (g) + e-
What factors affect ionisation energy and why?
Atomic radius: The greater the distance between the nucleus and the outer electrons, the less attraction
Nuclear charge: The more protons there are, ( larger the proton number ), the greater the attraction between the nucleus and the outer electrons.
Electron shielding: Electrons are negatively charged and so the inner-shell electrons repel outer-shell electrons, this is the shielding effect and will reduce attraction between the outer shell electrons and the nucleus.
Why does helium have a higher second ionisation energy than the first ionisation energy?
After the first electron is lost, the single electron is pulled closer to the helium nucleus, meaning the nuclear attraction on the remaining electron increases and more ionisation energy is required.
What is the definition for the second ionisation energy?
The energy required to remove one electron from each ion in one mol of gaseous 1+ ions of an element to form one mol of gaseous 2+ ions,
What does a large increase between seventh and eighth ionisation energies show?
A large difference in ionisation energies show that the eighth electron must be removed from a different energy shell, closer to the nucleus with less shielding.
What can you predict from successive ionisation energies?
The number of electrons on the outer shell
The group of the element in the periodic table
The identify of an element
There is a steady increase in ionisation energies and then there is a large difference in ionisation energies between third and fourth ionisation energies. What group would this element be in?
Since there is a large difference between the third and fourth ionisation energies, then it is likely the fourth electron is being removed another shell.
Therefore there are three electrons in the outershell and must be in group 3.
Why do first ionisation energies generally decrease down the group?
As you go down a group the atomic radius will increase, there is more electron shielding therefore nuclear attraction decreases and therefore less ionisation energy is required to removed the first electron.
Why does first ionisation energy generally increase across a period?
The nuclear charge will increase as the proton number increases, there is the same amount of shells so similar shielding, nuclear attraction will increase, atomic radius will decrease therefore first ionisation energy increases.
Across period 2 and 3, the first ionisation energy drops every so often. For example between Be -> B and N-> O. Why does this occur?
{Hint it has to do with the existence of subshells)
This is because it indicates the filling of the 2P subshell. Electrons in a 2P subshell are easier to remove than in a 2S subshell hence the first ionisation energy is lower.
Why is there a fall in ionisation energies between nitrogen and oxygen even though they both have their most outer electrons in the 2P subshell?
In oxygen, there are paired electrons in the 2P subshell whereas in nitrogen the electrons are not paired. In oxygen, since they repel, it makes it easier to remove an electron from oxygen than nitrogen
