ionisation energy Flashcards
What is ionisation energy?
It is a measure of the energy required to completely remove an electron from an atom of an element, this is done to form an ion
What is first ionisation energy?
The energy required to remove one electron from each atom in one mole of the gaseous element to form one mole of gaseous 1+ ions
X(g) -> X^+ + e^-
What is second ionisation energy?
X^+ (g) -> x^2+ (g) + e^-
What are factors affecting ionisation energy?
The negative electrons are attracted to the tiny positive nucleus, this attraction keeps the electrons held in their shells .
When an ion is formed, energy is supplied to remove an electron(s), the electrons in the valence shell are lost first as they experience the smallest amount of nuclear attraction and require the smallest ionisation energy .
Ionisation energy is largely influenced by atomic radius
How is Ionisation energy is largely influenced by atomic radius?
Because the larger the radius, the less nuclear attraction.
This is affected by nuclear charge and electron shielding
What is the atomic radius?
Atomic radius: the distance from the centre of the atom to the edge of the electron cloud , the boundary of the electron cloud is not incredibly well defined, instead a value for the distance between 2 nuclei is found an halved
What is the trend in atomic radius ?
Across a period the radius decreases, down a group the radius increases (largest being caesium, smallest being helium )
Why do we see such a trend in atomic radius in the periodic table?
Across a period:
The number of protons I n the nucleus increases, as it increases the effective nuclear charge also increases making the nucleus more positive.
Down a group:
The number of atomic shells increases and the inner shells of electrons repel the outer shell electrons as the electrons are negative and they will repel each other . This is shielding
Why do we see such trend across a period and down a group?
As we move across a period, elements increase in both the number of protons and electrons, as more electrons are added to the shell there is an increase in repulsion this is offset by the increases n effective nuclear charge and resulting in attractive forces
Why does a larger atomic radius affect ionisation energy ?
The larger the atomic radius, the further away the valence electrons are held from the nucleus, the further away the valence electrons are held , the smaller the nuclear attraction for the outer electrons will be.
What are trends in first ionisation energy?
Periodicity:
Across a period there is a general increase in first ionisation energyn because the proton number in the nucleus increases and the number of valence electrons increases. The outer shell is drawn inwards and shielding doesn’t change as there are the same number of shells
Down a group there is a general decrease in first ionisation energy . This is as the Buber of shells increases so the atomic radius increases and shielding increases although the umber of protons does increase, this is outweighed by the increase in atomic radius
