📖 Lesson 3: Elements, Compounds, and Mixtures

👩🏽‍🏫 Introduction

Hello again, science sleuth! 🕵🏽

Have you ever cooked jollof rice? You combine rice, tomatoes, oil, spices—and voilà, you have a tasty meal. But did you know that science also “mixes” things to form new substances?

In this lesson, we’ll learn the difference between elements, compounds, and mixtures. These are the basic forms in which matter exists, and knowing how to identify them helps you understand how everything—yes, everything—is made!

📘 Core Concepts

🔹 What is an Element?

An element is a pure substance made of only one kind of atom. It cannot be broken down into simpler substances.

• Examples:

  • Oxygen (O) – in the air

  • Iron (Fe) – used in construction

  • Gold (Au) – used in jewelry

There are 118 known elements, and about 92 occur naturally. All are listed in the Periodic Table.

🔹 What is a Compound?

A compound is a substance formed when two or more elements chemically combine in fixed proportions.

• Example:

  • Water (H₂O) = 2 atoms of hydrogen + 1 atom of oxygen

  • Salt (NaCl) = sodium + chlorine

Compounds:

• Have different properties from the elements that make them.

• Can only be separated by chemical means (not physically).

🔹 What is a Mixture?

A mixture contains two or more substances that are not chemically combined.

• Examples:

  • Air (a mixture of gases like oxygen and nitrogen)

  • Salad 🥗 (a mix of vegetables)

  • Seawater 🌊 (water + salt + minerals)

Mixtures:

• Can be separated by physical methods (e.g., filtering, boiling).

• Keep the properties of their individual parts.

🧪 Real-Life Examples

🧬 Comparing Elements, Compounds, and Mixtures

🧩 Sample Problem Walkthrough

🧠 Problem:

You’re given three substances:
(1) Iron filings,
(2) Salt (NaCl),
(3) A mixture of sand and salt.
How would you classify each one?

✅ Step-by-Step Solution:

1. Iron filings → One type of atom (Iron) → Element

2. Salt (NaCl) → Sodium + Chlorine chemically combined → Compound

3. Sand and Salt → Two substances mixed, not chemically joined → Mixture

✔️ Final Answer:

• Iron filings → Element

• Salt → Compound

• Sand + Salt → Mixture

✍🏽 Practice Exercises

Exercise 1: Fill-in-the-Blanks

1. A compound is formed when two or more ______ combine chemically.

2. A mixture can be separated by ______ means.

3. Water is a ______ because it contains hydrogen and oxygen.

Answers:

1. elements

2. physical

3. compound

Exercise 2: Multiple Choice

1. Which of the following is a compound?
   A. Oxygen
   B. Iron
   C. Salt
   D. Air
   Answer: ✅ C. Salt

2. Which statement is true about mixtures?
   A. They have fixed ratios
   B. Their parts are chemically combined
   C. They keep individual properties
   D. They can’t be separated
   Answer: ✅ C. They keep individual properties

Exercise 3: Classify These Substances

Answers:

• Carbon dioxide → Compound

• Milk → Mixture

• Hydrogen gas → Element

• Orange juice → Mixture

🌀 Recap

Let’s review what we’ve learned:

• Elements: Pure substances with one type of atom (e.g., Gold, Oxygen).

• Compounds: Formed by chemical bonds between elements (e.g., Water).

• Mixtures: Physical combinations of substances (e.g., Air, Salad).

• Compounds have fixed ratios; mixtures do not.

💭 Reflection Prompt

Pick three things around you right now—maybe in your kitchen, bedroom, or schoolbag. Can you classify each one as an element, compound, or mixture? Write your choices and reasons in your science journal!