smc-4257-30-Ionisation Energy

CHEMISTRY, M1 EQ-Bank 28

Using your understanding of periodic trends, explain and predict the differences in the properties of the elements lithium (Li) and fluorine (F) regarding their:

- atomic radii
- first ionisation energy
- electronegativity

Justify your predictions based on their positions in the periodic table and electronic configurations. (4 marks)

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Atomic Radii:

→ Lithium, being in the same period but a different group than fluorine, has fewer protons and a less effective nuclear charge, resulting in a larger atomic radius.

First Ionisation Energy:

→ Fluorine has a higher first ionisation energy due to its greater nuclear charge and smaller radius, which strongly attracts electrons.

Electronegativity:

→ Fluorine, being one of the most electronegative elements, has a strong ability to attract bonding electrons.

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Atomic Radii:

→ Lithium, being in the same period but a different group than fluorine, has fewer protons and a less effective nuclear charge, resulting in a larger atomic radius.

First Ionisation Energy:

→ Fluorine has a higher first ionisation energy due to its greater nuclear charge and smaller radius, which strongly attracts electrons.

Electronegativity:

→ Fluorine, being one of the most electronegative elements, has a strong ability to attract bonding electrons.

CHEMISTRY, M1 2009 HSC 30c

The graph shows the first ionisation energy of some elements.

Account for the trends in the graph in terms of the electron configuration of the elements. (3 marks)

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→ The increase in ionisation energy from Z=2 to 10 and Z=11 to 18 relates to the increase in effective nuclear charge across periods 1 and 2 respectively.

→ The same valence shell is being filled across a period, hence inner shell shielding and nucleus – shell distance is approximately constant while the nuclear charge increases.

→ Hence the electron binding force increases, requiring greater energy to remove a valence shell electron. Therefore, the ionisation energy increases across a period.

→ When the next valence shell begins to fill, as occurs at Z=3, 11 and 19 , the ionisation energy drops substantially because the electron experiences increased inner shell nuclear shielding and is further from the nucleus.

→ The generally lower ionisation energies for the second period elements compared to the first period elements also reflects the filling of higher valence shells.

→ This reflects the decrease in ionisation energy down a group in the periodic table.

CHEMISTRY, M1 2013 HSC 20 MC

The structures of ozone and molecular oxygen are shown.

Ozone is more easily decomposed than molecular oxygen because

it is polar.
it is a bent molecule.
it has a greater molecular mass.
it has a lower average bond energy.

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`D`

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→ The presence of the single bond in the ozone molecule lowers the average bond energy.

→ Bond breaking is an endothermic process and so requires energy. As ozone has a lower average bond energy, less energy is required to break the bonds and thus decomposes more easily than molecular oxygen.

`=>D`