Ionisation energy

Ionisation energy

Definition:

• Ionisation energy is the energy required to remove one mole of electrons from one mole of atoms in the gaseous state.

First Ionisation Energy:

• The first ionisation energy measures the energy involved in removing the first electron from an atom.
• Example: The first ionisation energy of magnesium represents the energy required to remove one mole of electrons from one mole of gaseous magnesium atoms.

Second Ionisation Energy:

• The second ionisation energy measures the energy required to remove a second mole of electrons from an atom.
• Example: The second ionisation energy of magnesium represents the energy needed to remove a second mole of electrons after the first electron has already been removed.

Third Ionisation Energy:

• The third ionisation energy involves removing an electron from an energy level that has already lost one or more electrons.
• Example: The third ionisation energy of magnesium is significantly higher because it requires removing an electron from the second energy level after the first electron has been removed.

Trends in Ionisation Energy:

• Across a period (from left to right) in the periodic table, ionisation energy increases. This is because the increasing nuclear charge exerts a stronger pull on the electrons, requiring more energy to remove them.
• Down a group (from top to bottom), ionisation energy decreases. This is due to the shielding effect of the outer electrons, which reduces the effective nuclear charge, making it easier to remove electrons.

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Ionisation energy

Summary:

• Ionisation energy measures the energy needed to remove electrons from atoms. It increases across a period and decreases down a group in the periodic table due to changes in nuclear charge and shielding effects.