Understanding Electron Affinity in Oxygen Family

Electron affinity is the energy change when an atom gains an electron to form a negative ion. For the oxygen family (Group 16: O, S, Se, Te, Po), the trend is not perfectly regular due to atomic size and electronic repulsion effects.

Step 1: Know the Elements and Their Order

The oxygen family members in periodic order: Oxygen (O), Sulfur (S), Selenium (Se), Tellurium (Te), Polonium (Po).

Step 2: Recall the Experimental Values

First electron affinity values (in kJ/mol) are approximately:

• O: -141
• S: -200
• Se: -195
• Te: -190
• Po: -180 (estimated)

Step 3: Analyze the Trend

From O to S, electron affinity increases (becomes more negative) due to smaller atomic size. From S onward, it decreases (less negative) because larger atomic size reduces effective nuclear attraction, despite increasing nuclear charge.

Step 4: Identify the Correct Graph Shape

The graph should show a peak at sulfur (S), with oxygen (O) having lower affinity, and subsequent elements (Se, Te, Po) showing a gradual decrease. This creates a curve that rises to a maximum at S and then falls.

Final Answer

The correct graph is the one where the value is highest at sulfur (second element in the group) and lower for oxygen and the subsequent elements. Based on the options provided (though images cannot be displayed here), it is typically the graph with a distinct peak at the second position.

Related Topics

• Periodic Trends: Electron affinity generally increases across a period and decreases down a group, but exceptions occur due to electronic stability and size effects.
• Atomic Structure: Size and effective nuclear charge influence an atom's ability to attract additional electrons.
• Group 16 Elements: Also known as chalcogens, they have six valence electrons and show variable oxidation states.

Key Formulae and Theory

Electron affinity (EA) is expressed as: $X\left(g\right)+e^{-}\to X^{-}\left(g\right); \Delta H=EA$

Factors affecting EA:

• Atomic size: Smaller atoms have higher EA due to closer proximity of nucleus to incoming electron.
• Electronic configuration: Half-filled or fully filled subshells may lower EA due to stability (e.g., oxygen has lower EA than sulfur because adding an electron to O's half-filled p-subshell faces more repulsion).
• Nuclear charge: Higher effective nuclear charge increases EA, but size often dominates down a group.