Chemistry / core

Compound

Also known as: chemical compound

definition

A pure substance composed of two or more different elements chemically bonded together in a fixed ratio, whose properties differ entirely from those of its constituent elements and can only be separated by chemical means. Most materials in daily life are compounds, not pure elements.

This concept is covered in depth in our understanding chemistry terms guide, with worked examples, practice problems, and common mistakes.

💡 Intuition

Elements joined together to make something new with different properties.

Core Idea

Compounds have fixed proportions and properties different from their elements.

Formal View

A compound is a pure substance with a definite composition described by a chemical formula. According to the law of definite proportions (Proust's law), a given compound always contains the same elements in the same mass ratio regardless of its source or method of preparation.

🔬 Example

Water (\text{H}_2\text{O}): hydrogen + oxygen. Salt (\text{NaCl}): sodium + chlorine.

🎯 Why It Matters

Most materials in daily life are compounds, not pure elements. Water, salt, sugar, plastics, and medications are all compounds. Understanding compounds is essential for cooking, medicine, agriculture, and manufacturing.

⚠️ Common Confusion

A compound is different from a mixture—compounds are chemically bonded.

How to Use Compound

When this concept appears in chemistry, it usually controls how you interpret a representation, a quantity, or a change in a system. Students make faster progress when they can explain what compound tells them before reaching for an equation or memorized phrase.

A strong self-check is to say what compound does, what it does not do, and which nearby idea it is easiest to confuse with. That kind of explanation makes later calculations, lab reasoning, and compare pages much more reliable.

💭 Hint When Stuck

When identifying whether a substance is a compound, check two things. First determine if it contains two or more different elements (if only one element, it is an element, not a compound). Then check if the elements are chemically bonded in fixed ratios (if just mixed physically, it is a mixture). Finally, verify that the substance has different properties from its component elements.

Related Concepts

Prerequisites

Next Steps

How Compound Connects to Other Ideas

To understand compound, you should first be comfortable with element and molecule. Once you have a solid grasp of compound, you can move on to mixture.

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Go Deeper

Want the Full Guide?

This concept is explained step by step in our complete guide:

Chemistry Terms and Definitions: Product, Reactant, Solution, Base, Molecule →

Frequently Asked Questions

What is Compound in Chemistry?

A pure substance composed of two or more different elements chemically bonded together in a fixed ratio, whose properties differ entirely from those of its constituent elements and can only be separated by chemical means.

Why is Compound important?

Most materials in daily life are compounds, not pure elements. Water, salt, sugar, plastics, and medications are all compounds. Understanding compounds is essential for cooking, medicine, agriculture, and manufacturing.

What do students usually get wrong about Compound?

A compound is different from a mixture—compounds are chemically bonded.

What should I learn before Compound?

Before studying Compound, you should understand: element, molecule.

Visualization

Static

Visual representation of Compound