2.6 Ionisation Energy Flashcards
What is ionisation energy?
Minimum amount of energy required to remove an electron from a gaseous atom
M(g) —> M+(g) + e-
What does the ionisation energy for hydrogen represent?
Minimum energy for the removal of an electron from level 1 to infinity where the energy level comes together.
How can the ionisation energy be worked out?
Fromt h frequency of the light at the convergence limit using E=hv
What is the equation for the second ionisation energy?
M+(g) —-> M2+(g) + e-
What is the equation for the nth ionisation energy?
M^(n-1)+(g) —–> M^n+(g) + e-
What is important about the second ionisation energy compared tot he first?
The second ionisation is always higher than the first.
Why is the second ionisation energy higher than the first?
Once an electron has been removed from an atom a positive ion is created. A positive ion attracts a negatively charged electron more strong than a neutral atom does, therefore more energy is needed to removed an electron from a positive ion than from a neutral atom.
Once an electron has been removed from an atom there is less repulsion between the remaining electrons. They are therefore pulled in closer to the nucleus. if they are closer to the nucleus they re more strongly attracted and more difficult to remove.
What is important about the graph for successive ionisation energies for an element (in this case Silicon)?
There is a large jump after the fourth ionisation energy- the fourth electron is removed from the third main energy level and the fifth electron is removed from th second main energy level - an electron int he second main energy level is closer to the nucleus and less shielded therefore it is more strongly attracted.
What is the trend in ionisation energies across a period?
Ionisation energy increase from left to right across period.
How can the general trend in first ionisation energy across period 2 in the periodic table be explained?
Nuclear charge increases from Li (3+) to Ne (10+) as protons are added to the nucleus.
The electrons are removed from the same main energy levels and electrons in the same energy level do not shield each other very well.
Therefore the force of attraction from the nucleus on the outer electrons increases from left to right across the period and the outer electron is more difficult to remove for neon.
The neon atom is also smaller than the lithium atom and therefore the outer electron is closer to the nucleus and more strongly held.
What is the explanation for why boron has a lower first ionisation energy then beryllium?
The electron configuration of Be is 1s22s2 and B is 1s22s22p1, the electron to be removed from the boron atom is in a 20 sub level whereas it is in a 2s sub level in beryllium. The 2p sub level in B is higher than the 2s sub level in Be and therefore less energy is required to remove an electron from B.
