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Ionisation Energies

The document discusses ionization energies, including definitions, factors affecting ionization energies such as nuclear charge and shielding, and trends in ionization energies down groups and across periods. Specifically, it notes that ionization energies decrease down groups as electrons are further from the nucleus and experience more shielding. Across periods, ionization energies generally increase as nuclear charge increases, though there are some exceptions due to subshell effects. Multiple ionization energies are measured from the ion produced in the previous ionization.

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Hena Afridi
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27 views15 pages

Ionisation Energies

The document discusses ionization energies, including definitions, factors affecting ionization energies such as nuclear charge and shielding, and trends in ionization energies down groups and across periods. Specifically, it notes that ionization energies decrease down groups as electrons are further from the nucleus and experience more shielding. Across periods, ionization energies generally increase as nuclear charge increases, though there are some exceptions due to subshell effects. Multiple ionization energies are measured from the ion produced in the previous ionization.

Uploaded by

Hena Afridi
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as PDF, TXT or read online on Scribd
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Ionisation energies

Definition

Factors

Trends

Down group 2

Across Period 3
Definition

The first ionisation energy is the energy required to


remove one mole of electrons from one mole of
gaseous atoms.

Na(g) → Na+(g) + e-
Must use state symbol (g)

remember 1 mole of atoms

In summary - the higher the IE, the harder it is to remove an


electron
Factors affecting IE

Nuclear charge

● Number of protons in the nucleus - the more there are, the stronger
the attraction for the electrons

Distance from nucleus

● The greater the distance from the nucleus the less the attraction
between protons and electrons. Distant electrons easier to remove.

Shielding (screening)

● As the number of electrons between the nucleus and the outer


electrons increases, the pull of the nucleus on the outer electrons is
lessened
Shielding
Trends

Down a group (Group 2)

Each time you move down a group, you have moved up to


the next “shell” / energy level.

What is the effect? Why? Discuss!


Trends

Down a group (Group 2)

Each time you move down a group, you have moved up to the next “shell” / energy
level.

The electron is FURTHER AWAY from the nucleus

The inner electrons SHIELD the charge from the nucleus


Trends

Across a period (Period 3)

General trend is to increase. However it isn’t as


simple as that!
can we explain this trend?
Filling 3s orbital Filling 3p orbital
doubling up
Filling 3p orbital
Singularly
Trend across a period

General trend - increasing. Adding more protons (nuclear


charge) into the same energy level / “shell”

Generally there is little extra shielding as it is the same shell.

Small drops between Gp1 and 2

● Mg -> Al the electron in Al is in a 3p orbital which is a


slightly higher energy so further away (easier to remove)
● Overides the effect of adding in another proton (providing
evidence for subshells)
Trend across a period

Small drops between Gp5 and 6

● P -> S the electron in S sharing a 3p orbital, electrons


repel each other (easier to remove)
● Shielding is identical for both
Multiple IE

O(g) → O+(g) + e-
O+(g) → O2+(g) + e- Subsequent IEs are measured
from the previous ion
O2+(g) → O3+(g) + e-

1st I.E. = 577 kJ mol-1

2nd I.E. = 1820 kJ mol-1

3rd I.E. = 2740 kJ mol-1

4th I.E. = 11600 kJ mol-1


Multiple IE

Subsequent IEs are measured


from the previous ion

1st I.E. = 577 kJ mol-1

2nd I.E. = 1820 kJ mol-1

3rd I.E. = 2740 kJ mol-1

4th I.E. = 11600 kJ mol-1

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