Chemistry - Ionisation energies

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What is the first ionisation energy of an element?

the energy required to remove one mole of its most loosely held electrons from one mole of gaseous atoms to form one mole of gaseous 1+ ions

Why does the first ionisation energy of atoms generally increase across a period

the nuclear charge increases but the shielding remains the same

Why is the first ionisation energy of boron (1s² 2s² 2p¹) less than that of beryllium (1s² 2s² )

B has one more proton in the nucleus than Be but there are also 2 extra inner sub-shell electrons. These cancel out the charge of two more of the protons, leaving an effective nuclear charge of only +1. This is less than Be (+2) so the electrons are less strongly attracted to the nucleus and thus less difficult to remove.

why do first ionisation energies decrease down a group?

the effective nuclear charge stays the same but the number of inner shells increases. The repulsion between these inner shells and the outer electrons makes them less stable, pushes them further from the nucleus and makes them easier to remove.

why does helium have the highest first ionization energy of all the elements?

its valence electrons are held extremely close to the nucleus with a strong positive charge and virtually no electron shielding

why is the successive ionisation energy of an atom always greater than the preceding one

As more electrons are removed from an atom, the number of electrons remaining in the atom decreases. The repulsion between these electrons therefore decreases, while the number of protons remains the same. The remaining electrons are thus more stable and increasingly difficult to remove.

why is the second ionisation energy of sodium much greater than the first

removing the second electron requires breaking into a stable, full octet shell

why does atomic size decrease across a period?

Atomic size decreases across a period because the number of protons increases while electrons are added to the same energy level, increasing effective nuclear charge and pulling electrons closer to the nucleus.

why does atomic size increase down a group?

Each successive element down a column has an extra occupied main energy level placing the valence electrons further away from the nucleus

The amount of energy required to remove an electron from an atom depends on what?

the number of protons in the nucleus of the atom and on the electronic configuration of that atom.

Explain the trends in this graph

lowkey need a essay

What is nuclear charge?

the number of protons in the nucleus

What is shielding?

the way inner-shell electrons block outer valence electrons from feeling the full positive pull of protons in the nucleus

what is effective nuclear charge?

• the net positive charge experienced by an electron in a multi-electron atom

• It is always less than the actual nuclear charge (Z) because inner-shell core electrons shield the outer electrons from the full pull of the positive protons

When considering trends in ionisation energies, which four factors should be considered?

• nuclear charge

• shielding

• effective nuclear charge

• electron repulsion

What is the formula for effective nuclear charge?

Z_eff = Z - S

Z: atomic number

S: core electron count

Why does ionisation energy decrease from group || to group |||

in group III the electrons are removed from a p-orbital, so it is shielded by the s-electrons in the outer shell. Thus the effective nuclear charge decreases.

why do first ionisation energies decrease from group V to group VI

the electron removed from the group VI atom is paired, so there is more repulsion between the electrons and the electron is easier to remove.

What is second (successive) ionisation energy

• The second ionisation energy is the minimum amount of energy required to remove one electron from each ion in one mole of gaseous 1+ ions, forming one mole of gaseous 2+ ions

• M_(g)⁺ —> M_(g)²⁺ + e^-

How can third ionisation energy be defined

• The third ionization energy is the energy required to remove the third electron from a gaseous, an ion with a +2 charge to form a tripositive cation +3 charge

• M_(g)²⁺ —> M_(g)³⁺ + e

How can the nth ionisation energy be defined

the energy required for the process;

M_(g)^(n-1)+ —> M_(g)ⁿ⁺ + e