Electron affinity

Definition

Electron affinity is the amount of energy released when an atom in the gas phase gains an electron to form a negatively charged ion. This concept is crucial for understanding how atoms interact and bond with each other, particularly as it relates to the position of elements on the periodic table and their electron configurations. Elements with high electron affinity tend to attract electrons more strongly, influencing their chemical reactivity and the types of bonds they can form.

5 Must Know Facts For Your Next Test

1. Electron affinity values generally become more negative as you move from left to right across a period in the periodic table, indicating a stronger attraction for electrons.
2. Noble gases typically have low or even positive electron affinity values because their outer electron shells are already full, making them less likely to gain additional electrons.
3. Halogens have high electron affinity values, which explains their strong tendency to form negative ions and react vigorously with metals.
4. The trend in electron affinity can vary across different groups; for example, alkaline earth metals usually have lower electron affinities compared to alkali metals.
5. The measurement of electron affinity is usually expressed in units of kilojoules per mole (kJ/mol), reflecting the amount of energy released during the electron gain process.

Review Questions

• How does electron affinity influence the reactivity of elements on the periodic table?
  • Electron affinity significantly influences the reactivity of elements because it indicates how readily an atom will gain an electron. Elements with high electron affinities, like halogens, readily accept electrons, leading to strong chemical reactions, particularly with metals. Conversely, elements with low electron affinities may not participate in reactions that involve gaining electrons as readily, affecting their overall reactivity.
• Compare and contrast the trends in electron affinity as you move across a period and down a group in the periodic table.
  • As you move across a period from left to right, electron affinity generally increases (becomes more negative), indicating that elements are more likely to gain electrons. In contrast, as you move down a group, electron affinity tends to decrease (becomes less negative) because added energy levels increase the distance between the nucleus and the incoming electron, reducing its attraction. These trends reflect underlying changes in atomic structure and effective nuclear charge.
• Evaluate how understanding electron affinity can help predict the behavior of certain elements in chemical reactions.
  • Understanding electron affinity allows chemists to predict how certain elements will behave in chemical reactions based on their likelihood of gaining electrons. For instance, knowing that halogens have high electron affinities informs us that they will readily accept electrons and form anions, which influences their ability to react with metals. This insight helps chemists design reactions and synthesize compounds by anticipating which elements will combine based on their tendency to gain or lose electrons.

Related terms

ionization energy: The energy required to remove an electron from a neutral atom in the gas phase, often used in conjunction with electron affinity to explain an element's reactivity.

electronegativity: A measure of an atom's ability to attract and hold onto electrons when forming chemical bonds, closely related to both electron affinity and ionization energy.

anion: A negatively charged ion that is formed when an atom gains one or more electrons, a direct result of the process described by electron affinity.