4.3.1 Atomic Radius Explained

Key Concepts

1. Definition of Atomic Radius

Atomic radius is a measure of the size of an atom, typically defined as half the distance between the nuclei of two identical atoms that are bonded together.

2. Factors Affecting Atomic Radius

Atomic radius is influenced by several factors, including the number of electron shells, nuclear charge, and electron shielding.

3. Trends in Atomic Radius Across the Periodic Table

Atomic radius generally decreases across a period from left to right and increases down a group.

Detailed Explanation

Definition of Atomic Radius

Atomic radius is a measure of the distance from the nucleus to the outermost electron shell. It provides insight into the size of an atom and its ability to attract bonding electrons.

Factors Affecting Atomic Radius

The number of electron shells (energy levels) increases down a group, causing the atomic radius to increase. The nuclear charge increases across a period, pulling the electrons closer to the nucleus and decreasing the atomic radius. Electron shielding, where inner electrons block the outer electrons from the full attractive force of the nucleus, also affects atomic radius.

Trends in Atomic Radius Across the Periodic Table

Across a period, atomic radius decreases because the increasing nuclear charge pulls the electrons closer to the nucleus. Down a group, atomic radius increases because the addition of electron shells results in a greater distance between the nucleus and the outermost electrons.

Examples and Analogies

Example: Period 2 Elements

In Period 2, lithium (Li) has the largest atomic radius, while neon (Ne) has the smallest. This decrease in radius from lithium to neon is due to the increasing nuclear charge across the period.

Analogy: Atomic Radius as a Sphere

Think of an atom as a sphere. As you add more layers (electron shells) to the sphere, it gets bigger. However, if you increase the strength of the core (nuclear charge), it pulls the layers closer, making the sphere smaller.

Example: Group 1 Elements

In Group 1, the atomic radius increases from lithium (Li) to francium (Fr). This increase is due to the addition of electron shells as you move down the group, resulting in a larger atomic size.