Recording-2025-02-24T18_10_57.841Z

Key Concepts in Electron Affinity and Ion Formation

Electron Affinity

• Electron affinity refers to the energy change that occurs when an electron is added to an atom.

• When discussing electron affinity, we consider the trend of increasing favorability as the absolute value of electron affinity increases (becomes more negative).

• Elements in the upper right of the periodic table (e.g., halogens) generally have higher electron affinities, meaning they favorably gain an electron.

  • Example: Fluorine has a high electron affinity and is more favorable for adding electrons.

Effective Nuclear Charge

• When an electron is added, it feels an effective nuclear charge, which is the net positive charge experienced by the electron due to the nucleus.

• Inner electrons partially shield the outer electron from the full nuclear charge.

Trends in the Periodic Table

• Noble Gases: Stable electron configurations with full valence shells (octets), thus nonreactive.

• Alkali Metals: These have one valence electron and typically lose it to form cations (e.g., Na+).

• Halogens: Tend to gain one electron to form anions (e.g., Cl-).

Ion Formation

• Cations: Positively charged ions formed by metals losing electrons (e.g., Na → Na+).

• Anions: Negatively charged ions formed by nonmetals gaining electrons (e.g., Cl + e- → Cl-).

Octet Rule in Electron Configuration

• Elements in the s and p blocks tend to gain, lose, or share electrons to achieve a full outer shell (octet).

• Example: Oxygen has six valence electrons and tends to gain two electrons to form O2-.

  • Electronic Configuration: From oxygen (1s2 2s2 2p4) gaining two electrons, becomes stable as 1s2 2s2 2p6 (like neon).

• Elements like sulfur or selenium will behave similarly to oxygen, gaining two electrons to fill their p orbitals.

Specific Element Behaviors

• Fluorine and Chlorine: High electron affinities leading to stable anions (F- and Cl-).

• Alkali Metals (e.g., Lithium, Sodium): Have one valence s electron, lose it easily; form +1 charged cations.

• Alkaline Earth Metals (e.g., Beryllium, Magnesium): Lose two valence electrons to form +2 charged cations.

• Transition Metals: Show variable oxidation states; often form multiple types of cations.

Summary of Electron Behavior and Ion Formation

• Elements in the upper right (especially halogens) favor gaining electrons (are strong electron acceptors) due to their high electron affinity.

• Metals will lose electrons to become cations, whereas nonmetals generally gain to form anions.

• Periodic trends are useful in predicting how different elements will behave in chemical reactions.