Ionisation Energy

• What is ionisation?

  Removing electrons from an atom or molecule
• What is the first ionisation energy (IE₁)?

  Energy to remove 1 mole of electrons
• Under what conditions are ionisation energies measured?

  Standard conditions: 298 K and 100 kPa
• What does a lower ionisation energy indicate?

  It is easier to form a positively charged ion
• What is the ionisation reaction for sodium (Na)?

  Na(g) → Na⁺(g) + e^-
• What is the first ionisation energy of sodium (Na)?

  +496 kJ/mol
• What is the first ionisation energy of magnesium (Mg)?

  +738 kJ/mol
• Why is magnesium's first ionisation energy higher than sodium's?

  Magnesium has more protons in its nucleus
• What is the second ionisation energy (IE₂)?

  Energy to remove 1 mole of electrons from 1 mole of gaseous 1⁺ ions
• Why are second ionisation energies higher than first ionisation energies?

  Electrons are removed from positively charged ions
• What is the second ionisation energy of magnesium (Mg)?

  +1451 kJ/mol
• What trend occurs in first ionisation energy down Group 2?

  There is a decrease in first ionisation energy
• Why does first ionisation energy decrease down Group 2?

  Increasing number of electron shells and shielding
• What is the first ionisation energy of beryllium (Be)?

  +900 kJ/mol
• What trend occurs in first ionisation energy across Period 3?

  There is generally an increase in first ionisation energy
• What causes drops in first ionisation energy in Period 3?

  Subshell structure of the elements
• What is the first ionisation energy of chlorine (Cl)?

  +1251 kJ/mol
• Why does the first ionisation energy drop between magnesium and aluminium?

  Aluminium's outer electron is in a higher energy 3p orbital
• Why does the first ionisation energy drop between phosphorus and sulphur?

  Electrons in sulphur experience spin-pair repulsion
• What are the factors affecting ionisation energy?

  • Nuclear charge: More protons increase attraction
  • Distance from nucleus: Closer electrons have stronger attraction
  • Electron shielding: Inner electrons weaken pull on outer electrons
• What are the trends in ionisation energy down Group 2 and across Period 3?

  • Down Group 2: Decrease in first ionisation energy due to increased shielding and distance
  • Across Period 3: Generally increase in first ionisation energy with drops due to subshell structure
• How do successive ionisation energies change within an atom?

  • Successive ionisation energies increase as electrons are removed from increasingly positively charged ions
  • Large increases occur when a new shell is reached
• What is the significance of changes in ionisation energy?

  They can determine the electronic structure of an element
• What happens to the attraction between electrons and the nucleus as electrons are removed?

  The remaining electrons are attracted more strongly
• What is the general trend in ionisation energy as you move from left to right across a period?

  Ionisation energy generally increases
• What is the relationship between ionisation energy and the number of protons in an atom?

  More protons generally lead to higher ionisation energy
• How does the electron configuration of an element affect its ionisation energy?

  Electron configuration determines the energy levels and shielding
• What is the electron configuration of sodium (Na)?

  1s² 2s² 2p⁶ 3s¹
• What is the electron configuration of magnesium (Mg)?

  1s² 2s² 2p⁶ 3s²
• What is the electron configuration of aluminium (Al)?

  1s² 2s² 2p⁶ 3s² 3p¹
• What is the electron configuration of silicon (Si)?

  1s² 2s² 2p⁶ 3s² 3p²
• What is the electron configuration of phosphorus (P)?

  1s² 2s² 2p⁶ 3s² 3p³
• What is the electron configuration of sulfur (S)?

  1s² 2s² 2p⁶ 3s² 3p⁴
• What is the electron configuration of chlorine (Cl)?

  1s² 2s² 2p⁶ 3s² 3p⁵
• What is the electron configuration of argon (Ar)?

  1s² 2s² 2p⁶ 3s² 3p⁶
• What is the significance of the electron configurations of elements in Period 3?

  They determine the ionisation energies and chemical properties
• How can ionisation energy be used to infer the electronic structure of an element?

  Changes in ionisation energy indicate electron shell levels
• What happens to the ionisation energy when a new electron shell is reached?

  There is a large increase in ionisation energy
• What is the relationship between ionisation energy and the distance of electrons from the nucleus?

  Greater distance leads to lower ionisation energy
• How does electron shielding affect ionisation energy?

  Increased shielding reduces the effective nuclear charge felt