7.2 Ionisation Energies Flashcards
(21 cards)
What is the shielding effect?
The effect of inner electrons which reduces the pull of the nucleus on the electrons in the outer shell.
What is nuclear charge?
A measure of how positive the nucleus is
When does ionisation occur?
When atoms lose or gain electrons
What does ionisation energy refer to?
The energy needed to form positive ions
What is 1st ionisation energy?
The energy needed to remove one electron from each atom in one mole of gaseous atoms of an element to form one mole of gaseous 1+ ions
How are electrons held in their shells?
By attraction from the nucleus.
Which electron will be in the highest energy level?
The first electron lost in ionisation
What 3 factors affect the attraction between the nucleus and the outer electrons of an atom, and therefore the ionisation energy?
-Atomic radius
-Nuclear charge
-Electron shielding
How does atomic radius affect the ionisation energy?
-The greater the distance between the nucleus and the outer electrons, the less the nuclear attractions.
-The force of attraction falls off sharply with increasing distance
-So, ionisation energy decreases.
How does nuclear charge affect the ionisation energy?
-The more protons there are in the nucleus of an atom, the greater the attraction between the nucleus and the outer electrons
-So, ionisation energy increases
How does electron shielding affect the ionisation energy?
-Electrons are negatively charged, and so inner-shell electrons repel outer-shell electrons.
-This repulsion is called the shielding effect, and reduces the attraction between the nucleus and the outer electrons
-So as shielding increase, ionisation energy decreases.
How many ionisation energies will any given element have?
The same amount as the number of electrons it has.
What is second ionisation energy?
The energy required to remove one electron from each ion in one mole of gaseous 1+ ions of an element to form one mole of gaseous 2+ ions.
Is the second ionisation energy typically higher or lower than the first?
Higher
Why is the second ionisation energy typically higher than the first?
-Because after the first electron is lost, the next electron is pulled in closer to the nucleus.
-The nuclear attraction on the remaining electron increases, and more ionisation energy will be needed to remove this next electron.
What do successive ionisation energies allow predictions to be made about?
-The number of electrons in the outer shell
-The group of the element in the periodic table
-The identity of an element
What do large differences in ionisation energy suggest?
That the next electron must be removed from a different shell, closer to the nucleus, and with less shielding
Describe the trend of first ionisation energies going down a group.
-Going down a group, the number of inner shells increases
-Atomic radius increases
-More inner shells, so shielding increases
-First ionisation energy DECREASES
Describe the trend of first ionisation energies going across a period.
-Going across a period, nuclear charge increases
-Same shells, so similar shielding
-Nuclear attraction increases
-Atomic radius DECREASES
-So first ionisation energy INCREASES.
Explain why there is a drop in ionisation energy going from Beryllium to Boron, despite their positions in the periodic table.
-An extra electron has gone into one of the 2p orbitals in Boron, and it has gone to a new subshell, in an outer shell of a higher energy level
-So there is more electron shielding, so lower ionisation energy.
Explain why there is a drop in ionisation energy going from Nitrogen to Oxygen, despite their positions in the periodic table.
-In nitrogen and oxygen, the highest energy electrons are in a 2p subshell.
-In oxygen, the paired electrons in one of the 2p orbitals repel eachother, making it easier to remove an electron from an oxygen atom, than a nitrogen atom
-So ionisation energy decreases.
