Why does atomic radius increase down a group?

As you go down a group, new principal energy levels (electron shells) are added. The inner shells shield outer electrons from nuclear pull, expanding the atom's size.

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Core Study Guide

Periodic Table Trends

The systematic classification and properties of chemical elements.

Dmitri Mendeleev organized elements by properties, predicting missing ones. The modern table aligns elements by atomic number.

This unit covers atomic radius, ionization energy, electronegativity trends, and properties of key chemical families.

Key Takeaways

•Periodic trends are governed by effective nuclear charge and electron shielding.
•Atomic radius increases down a group but decreases left-to-right across a period.
•Noble gases are chemically inert due to full valence shells.

Core Concepts & Definitions

1Electronegativity and Ionization Energy

Ionization energy is the energy required to remove an electron. Electronegativity is the ability to attract electrons.

•Both trends increase up and to the right across the periodic table.

•Fluorine is the most electronegative element.

Quick Revision Notes

•Alkali metals (Group 1) are highly reactive; Halogens (Group 17) are highly reactive non-metals.
•Noble gases (Group 18) have stable s²p⁶ octet configurations.