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Trends in the Periodic Table Explained
Nov 22, 2024
Lecture on Periodic Table Trends
Introduction
Focus on trends in the periodic table.
Key trends to be discussed:
Atomic radius
Ionic radius
Metallic character
Electronegativity (part of electropositivity)
Ionization energy
Atomic Radius and Ionic Radius
Atomic Radius
Trend Down a Group
:
Atomic radius increases as you move down a group.
Increase in the number of protons (nuclear charge, Z) and electron shells.
Increased shielding effect due to more inner electron shells.
Effective nuclear charge decreases, leading to less attraction to valence electrons.
Trend Across a Period
:
Atomic radius decreases from left to right across a period.
Number of electron shells remains constant.
Increase in nuclear charge, Z, while shielding effect remains constant.
Valence electrons experience increased inward attraction, pulling them closer to the nucleus.
Ionic Radius
Metals
:
Metals lose valence electrons when forming positive ions.
Example: Sodium atom (Na) becomes smaller as it loses an electron to form Na+.
Positive ions are smaller than their neutral atoms.
Non-Metals
:
Non-metals gain electrons when forming negative ions.
Example: Phosphorus (P) gains electrons to become P³⁻, increasing in size.
Negative ions are larger than their neutral atoms.
Increased electron repulsion leads to a larger ionic radius.
Metallic Character and Electronegativity
Metallic Character and Electropositivity
Trend Down a Group
:
Valence electrons are held more weakly.
Easier to lose electrons, increasing electropositivity and metallic character.
Trend Across a Period
:
Harder to lose valence electrons across a period due to increased effective nuclear charge.
Metallic character decreases.
Electronegativity
Trend Down a Group
:
Decrease in electronegativity as electropositivity increases (easier to lose electrons).
Trend Across a Period
:
Increase in electronegativity as it becomes harder to lose electrons, making it easier to gain electrons.
Conclusion
Next video will cover ionization energy in detail.
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