Define first ionisation energy.

In the subtopic Electron configuration and ionisation energy, this AQA A-Level Chemistry 7405 learning objective focuses on define first ionisation energy. It belongs to Atomic structure, so revision should stay anchored to this exact subtopic rather than drifting into a generic GCSE-level chemistry summary. Approved keywords to use include ionisation energy. Ionisation energy trend. means the general pattern observed in ionisation energies across periods and groups in the periodic table, typically increasing across a period and decreasing down a group Avoid the mistake of students often confuse first ionisation energy with other forms of energy, such as total energy or binding energy; instead, first ionisation energy is defined as the energy required to remove one mole of electrons from one mole of gaseous atoms to form one mole of gaseous ions. To clarify, remember the formula: Ionisation Energy = Energy required to remove an electron from an atom. For example, for a sodium atom (Na), the first ionisation energy can be expressed as Na(g) → Na⁺(g) + e⁻. This shows that energy is needed to remove the electron, which is the essence of ionisation energy For exam answers, define first ionisation energy as the energy required to remove one mole of electrons from one mole of gaseous atoms to form one mole of gaseous ions