Assessing Acidity Qualitatively - Factor 1: Atom - YouTube

Exercise 3.13 - Assessing Acidity Qualitatively - Factor 1: Atom

Introduction

This video covers Exercise 3.13, focusing on assessing acidity qualitatively by examining the atom to which the hydrogen is bonded. The discussion introduces a mnemonic device, REO, to help remember the four key factors that influence acidity: Atom, Resonance, Induction, and Orbitals.

Main Points

• Atom Factor:

- The first factor to consider in assessing acidity is the atom to which the hydrogen is bonded.

- Column Trend: In a column of the periodic table, hydrogen on an atom further down the column is more acidic because larger atoms can better stabilize the negative charge left behind.

- Row Trend: In a row of the periodic table, hydrogen on an atom further to the right is more acidic because more electronegative atoms can better stabilize the negative charge.

• Why Atoms Matter:

- Column Trend Explanation:

    - As you go down a column, atoms become larger.
    - Larger atoms can spread out the negative charge more effectively, making the conjugate base more stable.

- Row Trend Explanation:

    - As you move to the right in a row, atoms become more electronegative.
    - More electronegative atoms pull the negative charge closer to the nucleus, stabilizing it better.

Examples

• Example A:

- Blue hydrogen on oxygen, red hydrogen on carbon.

- Oxygen and carbon are in the same row; oxygen is to the right.

- The hydrogen on oxygen is more acidic due to higher electronegativity.

- Molecule with negative charge on oxygen is more stable than on carbon.

• Example B:

- Blue hydrogen on nitrogen, red hydrogen on carbon.

- Nitrogen and carbon are in the same row; nitrogen is to the right.

- The hydrogen on nitrogen is more acidic due to higher electronegativity.

- Molecule with negative charge on nitrogen is more stable than on carbon.

• Example C:

- Blue hydrogen on oxygen, red hydrogen on sulfur.

- Oxygen and sulfur are in the same column; sulfur is lower.

- The hydrogen on sulfur is more acidic due to the larger size of sulfur.

- Molecule with negative charge on sulfur is more stable than on oxygen.

• Example D:

- Blue hydrogen on nitrogen, red hydrogen on oxygen.

- Nitrogen and oxygen are in the same row; oxygen is to the right.

- The hydrogen on oxygen is more acidic due to higher electronegativity.

- Molecule with negative charge on oxygen is more stable than on nitrogen.

Conclusion

The video demonstrates how to use the atom factor to assess the relative acidity of different hydrogens in a molecule. By understanding the trends in columns and rows of the periodic table, one can determine which hydrogen is more likely to dissociate, making the molecule more acidic.