Defining Electron Affinity
Electron affinity is the change in energy that occurs when a neutral atom in the gaseous state gains an electron to form a negative ion. It is a direct measurement of an atom's ability to accept an electron. A more negative electron affinity value indicates a greater attraction for an electron, as energy is released during the process.
Section 2: Key Influencing Factors
The value of electron affinity is primarily influenced by atomic size and effective nuclear charge. Smaller atoms with a higher effective nuclear charge (a stronger pull from the nucleus on its outermost electrons) generally have a greater attraction for an additional electron. This results in a more negative, or more exothermic, electron affinity.
Section 3: A Practical Example with Halogens
A chlorine atom (Cl) is a perfect example. It has seven valence electrons and only needs one more to achieve a stable octet. When a chlorine atom gains an electron to become a chloride ion (Cl⁻), a significant amount of energy is released. This gives chlorine a very high (and thus very negative) electron affinity, reflecting its strong tendency to accept an electron.
Section 4: Importance in Chemistry
Electron affinity is a fundamental periodic property that helps predict an element's chemical behavior, especially its likelihood of forming anions and engaging in ionic bonding. It works alongside ionization energy and electronegativity to provide a complete picture of an atom's reactivity and bonding characteristics.