Lesson 4: 2.4 Structure of Metals and Alloys

What is the "electron sea model," and how does it explain why metals are malleable and ductile?
How do interstitial and substitutional alloys differ in their particulate packing and mechanical strength?

Delocalized Electrons
Sea of Electrons
Malleability
Ductility
Substitutional Alloy
Interstitial Alloy
Interstices

Learning Objective 2.4.A; Suggested Skill 1.A (Models and Representations)

Introduces metallic bonding via a rigid array of metal cations immersed in a delocalized cloud of valence electrons. Students must contrast substitutional alloys (atoms of similar radii replace each other) with interstitial alloys (small atoms fit into the interstitial spaces between large atoms), noting that interstitial alloys are typically harder and l

When talking about alloys, connect it to historical metallurgy—such as the transition from the Copper Age to the Bronze Age. Early civilizations mixed copper with tin to intentionally create a substitutional alloy (Bronze) that was significantly harder than copper alone, transforming tools, agriculture, and defense structural engineering across early societies globally.

Support: Provide a drawing page with pre-drawn grids of large iron atoms, and give students templates to draw small carbon circles in the empty cracks to visualize an interstitial alloy.
Extension: Have students evaluate a series of metal pairs (e.g., Cu/Zn vs. Fe/C) using a table of atomic radii, and predict which will form a substitutional alloy versus an interstitial alloy.

Sample Problem: Brass is an alloy composed of copper and zinc, which have atomic radii of 128pm and 134pm, respectively. Steel is an alloy composed of iron (126 pm) and carbon (77 pm).

1. Identify the specific type of alloy formed by brass and the type formed by steel.

2. Draw a particulate-level representation of a small section of steel, using distinct symbols for iron and carbon atoms. Ensure relative atomic sizes are represented accurately.