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The diagram shows a sketch of the trend in the first ionisation energies for the elements 3 to 10 in the periodic table - Leaving Cert Chemistry - Question (b) - 2003
Question (b)
The diagram shows a sketch of the trend in the first ionisation energies for the elements 3 to 10 in the periodic table. (b) (i) Account for the general increase in... show full transcript
Worked Solution & Example Answer:The diagram shows a sketch of the trend in the first ionisation energies for the elements 3 to 10 in the periodic table - Leaving Cert Chemistry - Question (b) - 2003
Step 1
Account for the general increase in ionisation energies across these elements:
Answer
The general increase in ionisation energies across elements 3 to 10 is attributed to two main factors:
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Increase in Nuclear Charge: As we move across a period in the periodic table, the number of protons in the nucleus increases. This results in a stronger effective nuclear charge experienced by the outermost electrons, meaning more energy is required to remove an electron.
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Decrease in Atomic Radius: The increasing nuclear charge pulls the electrons closer to the nucleus, leading to a reduction in atomic radius. A smaller atomic radius means that the outer electrons are held more tightly, again resulting in a higher ionisation energy.
Step 2
Explain why the ionisation energies of element number 4 and 7 are exceptionally high relative to the general trend:
Answer
The ionisation energies of element number 4 (Beryllium) and element number 7 (Nitrogen) are exceptionally high because:
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Element 4 (Beryllium): The outer electron configuration is s^2, where both s orbitals are fully occupied. This configuration imparts greater stability, thus requiring more energy to remove an electron compared to elements with partially filled orbitals.
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Element 7 (Nitrogen): Nitrogen has a half-filled p subshell configuration of p^3, which is particularly stable. The half-filled subshell offers additional stability due to the exchange energy associated with having equal distribution of electrons among the orbitals. This stability requires more energy to remove an electron, leading to higher ionisation energy.
Step 3
How does the definition of second ionisation energy differ from that of first ionisation energy?
Answer
The first ionisation energy is defined as the energy required to remove the most loosely bound electron from a neutral atom in its gaseous state:
In contrast, the second ionisation energy is the energy required to remove an electron from a positively charged ion:
Thus, the key difference lies in the charge of the species from which the electron is being removed: the first ionisation energy involves a neutral atom, while the second involves an already ionised atom.