(55) The Periodic Table: Atomic Radius, Ionization Energy, and Electronegativity

Introduction to the Periodic Table

• The periodic table organizes elements in a systematic way that reveals patterns in their properties.

• Initially, many formats for the periodic table were proposed, but Dmitri Mendeleev's arrangement proved effective due to its predictive abilities and correlation with existing data.

Mendeleev’s Table

• Arrangement: Elements are organized in rows (periods) and columns (groups).

• Similar Behavior: Elements within the same group share similar characteristics due to the same number of valence electrons.

• Prediction: Gaps in Mendeleev's table indicated the presence of undiscovered elements, which were later found to match his predictions.

Understanding Groups and Valence Electrons

• Group 1: One valence electron in the outermost shell.

• Group 2: Two valence electrons, and this continues for other groups, influencing elements' characteristics.

Periodic Trends

Atomic Radius

• Definition: The size of an atom.

• Trend:

  • Increases down a group due to the addition of electron shells.

  • Decreases across a period (to the right) due to increased nuclear charge attracting electrons more tightly.

Ionic Radius

• Definition: Size of an ion.

• Trend: Adding electrons results in a larger radius due to repulsion; removing electrons makes the ion smaller. Ions with the same electron configuration will see reduced radii as atomic number increases.

Ionization Energy

• Definition: Energy required to remove an outermost electron.

• Trend:

  • Increases across a period due to greater nuclear charge holding electrons tighter.

  • Decreases down a group as valence electrons are farther from the nucleus.

• Special Cases: Notable jumps in ionization energy occur when reaching a noble gas configuration (full electron shell).

Successive Ionization Energies

• The second ionization energy is greater than the first. Subsequent removals continue to increase in energy required.

• Special stability is observed in half-full or full sub-shells, which affects trends.

Electron Affinity

• Definition: Energy change when an atom gains an electron.

• Trend: Increases to the right of the periodic table (excluding noble gases), as elements like fluorine achieve a full outer shell by gaining an electron.

• Exceptions: Trends shift similarly to ionization energy due to stability in filled shells.

Electronegativity

• Definition: An atom's ability to attract electrons in a chemical bond.

• Trend: Increases across a period and decreases down a group due to effective nuclear charge.

• Special focus on fluorine as the most electronegative element.

Conclusion

• Key trends to remember:

  • Atomic radius increases down, decreases across.

  • Ionization energy, electron affinity, and electronegativity all increase across a period.

• Encourage further exploration of these concepts.