Atomic structure common mistakes

Common mistakes

• Misplacing the 4s and 3d subshells

  Assuming 3d fills before 4s for all elements.

  Fix itIn neutral atoms, 4s is filled before 3d, but in ions the 4s electrons are removed first. Always apply the Aufbau principle to the neutral atom before considering ionisation.

• Confusing ionisation energy with electron affinity

  Students often confuse ionisation energy with electron affinity, thinking they are the same.

  Fix itRemember that ionisation energy is the energy required to remove an electron, while electron affinity is the energy change when an electron is added to an atom.

• Confusing ionisation energy with ionisation potential

  Using the term 'ionisation potential' to refer to the energy required to remove an electron, leading to incorrect equations.

  Fix itIonisation potential is the energy required to remove an electron from a gaseous atom, but it is not used in equations; instead, use 'ionisation energy' and write the equation as X(g) → X⁺(g) + e⁻.

• Confusing ionisation energy with ionisation potential

  Students often state that ionisation energy is the same as ionisation potential, ignoring that ionisation potential is the energy required to remove an electron from a gaseous atom in the gas phase, whereas ionisation energy is the energy per mole.

  Fix itClarify that ionisation energy (kJ mol⁻¹) is the molar quantity, while ionisation potential (eV) is the energy per electron. Both describe the same process but are expressed in different units.

• Confusing ionisation energy with electronegativity

  Students often confuse ionisation energy with electronegativity.

  Fix itRemember that ionisation energy refers to the energy needed to remove an electron, while electronegativity measures an atom's ability to attract electrons in a bond.