Key idea
Electron affinity
Start with the central idea, then test it against a concrete element or example. A scientific model is useful when we know what it explains — and where its limits are.
Electron affinity
The key idea
Electron affinity describes the energy change associated with adding an electron to a gaseous atom or species, with sign conventions requiring careful attention.
Why it matters
Across the periodic table it reflects a competition between nuclear attraction, electron repulsion and the structure of available states.
A picture to remember
Convention used on Mendeleev
Mendeleev uses the
Some textbooks instead quote the attachment enthalpy itself. Its sign is opposite. To avoid ambiguity, Mendeleev never mixes these two conventions.
Key idea
Electron affinity
Guided example
Electron affinity
Start with the central idea, then test it against a concrete element or example. A scientific model is useful when we know what it explains — and where its limits are.
Put it into practice
Electron affinity
Choose a concrete case linked to Electron affinity. Write down the known information, what you are trying to find, and the units. Then state the rule, model or trend you will use. If a calculation is involved, keep the units visible at every line; if it is conceptual, state what changes and what remains fixed.
Check your answer
A strong answer contains four things: the starting situation, the variable that changes, the direction or numerical result, and one check. The check can be a unit, an order of magnitude, a limiting case or a comparison with a familiar example.