Ionisation Energy Periodic Trends

Ionisation Energy: Periodic Trends

Ionisation energy is the energy required to remove an electron from an atom in its ground state.

Periodic Trends:

Across a Period:

• Ionisation energy increases from left to right across a period due to:
  • Increased nuclear charge (more protons)
  • Decreased atomic radius (electrons are closer to the nucleus)
  • Increased effective nuclear charge (shielding effect decreases)

Down a Group:

• Ionisation energy decreases down a group due to:
  • Increased atomic radius (electrons are farther from the nucleus)
  • Decreased effective nuclear charge (shielding effect increases)
  • Addition of energy levels (screening effect)

Exceptions:

• Noble gases have higher ionisation energies than expected due to their full outer energy level, making it harder to remove an electron.
• Alkali metals have lower ionisation energies than expected due to their single electron in the outermost energy level, making it easier to remove.

Key Points:

• Ionisation energy is a measure of the energy required to remove an electron from an atom.
• Periodic trends in ionisation energy are due to changes in nuclear charge, atomic radius, and effective nuclear charge.
• Understanding these trends is crucial in explaining the properties and reactivity of elements.

Ionisation Energy: Periodic Trends

Trends Across a Period

• Ionisation energy increases from left to right across a period due to increased nuclear charge and decreased atomic radius.
• Electrons are closer to the nucleus, resulting in a stronger attraction, making it harder to remove an electron.
• The shielding effect decreases, allowing the nuclear charge to have a greater influence on the outermost electron.

Trends Down a Group

• Ionisation energy decreases down a group due to increased atomic radius and decreased effective nuclear charge.
• Electrons are farther from the nucleus, resulting in a weaker attraction, making it easier to remove an electron.
• The shielding effect increases, reducing the nuclear charge's influence on the outermost electron.
• Addition of energy levels leads to a screening effect, further decreasing ionisation energy.

Exceptions

• Noble gases have higher ionisation energies than expected due to their full outer energy level.
• Alkali metals have lower ionisation energies than expected due to their single electron in the outermost energy level.

Key Points

• Ionisation energy measures the energy required to remove an electron from an atom.
• Periodic trends in ionisation energy result from changes in nuclear charge, atomic radius, and effective nuclear charge.