Lesson 6.3: Substances' properties depend on their bonds

Lesson Focus

This lesson explores how the way atoms bond determines a substance's properties. We will examine metallic, ionic, and covalent bonds and see how they create unique characteristics in different materials.

Learning Objectives

• Describe how metal atoms bond together by sharing electrons, forming unique metallic bonds.
• Analyze how ionic and covalent bonds directly affect a substance's properties, like melting point and conductivity.
• Identify how different bonding arrangements create various forms of an element, such as carbon as diamond and graphite.

Metals conduct electricity because of metallic bonds. Their atoms release electrons into a shared "sea" that flows freely, carrying electrical current and heat. This structure also allows atoms to slide past one another, making metals easy to shape. Why can you bend a paperclip without it breaking but can't bend a salt crystal?

Ionic bonds form when positive and negative ions lock into a rigid crystal lattice, creating hard solids with very high melting points. This strong structure is brittle and a poor electrical conductor. However, when dissolved in water, the ions separate and can move, allowing the solution to conduct electricity.

Covalent bonds form individual molecules, resulting in compounds with low melting points and poor conductivity. Unlike the strong ionic lattice, these separate molecules require less energy to pull apart. Since they have no free charges, covalent compounds do not conduct electricity, even when dissolved. Think about why sugar melts but salt doesn't.

The same element can have different properties based on its atomic bonds. In diamond, each carbon atom forms four strong covalent bonds in a rigid 3D network, making it extremely hard. In graphite, carbon atoms bond in flat layers that slide easily, making it soft. This shows how structure determines properties.