Lecture Notes: The Periodic Table

Introduction

• The periodic table organizes all known chemical elements.
• Developed by Dmitri Mendeleev in the mid-1800s.
• Arranged in rows (periods) and columns (groups).
• Reveals patterns in element properties and behavior.

Mendeleev's Contribution

• Mendeleev's table successfully correlated data and predicted unknown elements.
• Elements in the same group have similar behaviors due to having the same number of valence electrons.

Periodic Table Structure

• Periods: Horizontal rows in the table.
• Groups: Vertical columns where elements show similar chemical behavior.
• Group 1: Elements have one valence electron.
• Group 2: Elements have two valence electrons.

Periodic Trends

Atomic Radius

• Increases down a group (more electron shells).
• Decreases across a period from left to right (increased nuclear charge pulling electrons closer).

Ionic Radius

• Electrons repel each other: Adding an electron increases size, removing one decreases size.
• Ions with the same electron configuration have decreasing radii as atomic number increases.

Ionization Energy

• Energy required to remove an electron from the outer shell.
• Increases across a period from left to right.
• Decreases down a group (electrons farther from nucleus).
• Exceptions due to orbital symmetry (e.g., nitrogen and oxygen).

Electron Affinity

• Energy change when an atom gains an electron.
• Increases across a period (excluding noble gases).
• Highest for elements wanting to achieve noble gas configuration, like fluorine.

Electronegativity

• Ability of an atom to attract electrons in a bond.
• Increases across a period, decreases down a group.
• Highest in small atoms with high effective nuclear charge, like fluorine.

Key Points

• Atomic radius trend: increases downwards and decreases rightwards.
• Ionization energy, electron affinity, and electronegativity: increase across a period.
• Understanding these trends helps in predicting element behavior in reactions.

Conclusion

• These fundamental concepts provide a foundation for learning more about chemical bonds in future lessons.
• Important to understand these trends for deeper comprehension of chemistry.

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