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Slide 1

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The periodic table
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Slide 2

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Trends in ionisation energy
The ionisation energy increases across a
period because:
Higher nuclear charge.
Increase in electrons but no increase in
energy levels.
This means no extra shielding.…read more

Slide 3

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Trends in ionisation energy
Ionisation energy decreases down a group
There is increased shielding from extra
energy levels.
There is more distance between the
outer electrons and the nucleus,
because of addition electron shells
(energy levels).
So less energy is required to remove an
electron.…read more

Slide 4

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Trends in Electron affinity
Electron Affinities Across a Period
Electron affinities becoming increasingly negative from left to right. Just as in
ionization energy, this trend conforms to and helps explain the octet rule. The octet
rule states that atoms with close to full valence shells will tend to gain electrons.
Such atoms are located on the right of the periodic table and have very negative
electron affinities, meaning they give off a great deal of energy upon gaining an
electron and become more stable. Be careful, though: the nobel gases, located in
the extreme right hand column of the periodic table do not conform to this trend.
Noble gases have full valence shells, are very stable, and do not want to add more
electrons: noble gas electron affinities are positive. Similarly, atoms with full
subshells also have more positive electron affinities (are less attractive of electrons)
than the elements around them.
Electron Affinities Down a Group
Electron affinities change little moving down a group, though they do generally become
slightly more positive (less attractive toward electrons). The biggest exception to
this rule are the third period elements, which often have more negative electron
affinities than the corresponding elements in the second period. For this reason,
Chlorine, Cl, (group VII and period 3) has the most negative electron affinity.
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Slide 5

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Trends in atomic
Increases down a group because:
Addition energy levels.
More distance between nucleus and
outer electrons.
So less attraction between protons
and outer electrons.…read more

Slide 6

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Trends in atomic
Decreases across a period because:
Electrons do not fill a new shell so
electrons are same distance from
So no extra shielding or distance.
This means that electrons are attracted
more strongly.…read more

Slide 7

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