Chapter focus
Classify materials by whether they contain one type of atom, chemically joined elements, or substances physically mixed together.
These are original study notes and practice questions prepared for revision. Use your assigned NCERT edition for the complete lesson, diagrams, activities, and exercise wording.
What you will learn
- Explain the main idea: Classify materials by whether they contain one type of atom, chemically joined elements, or substances physically mixed together.
- Use the key terms and relationships in the notes below.
- Show your reasoning and check whether an answer fits the question.
Key ideas and notes
- An element contains one kind of atom; a compound has elements chemically combined in a fixed proportion.
- A mixture contains substances physically combined and can often be separated by physical methods.
- A pure substance has a fixed composition; mixtures may be uniform or non-uniform.
Worked example
Air is a mixture because its gases are physically mixed and their proportions can vary.
Quick revision
An element contains one kind of atom; a compound has elements chemically combined in a fixed proportion.
A mixture contains substances physically combined and can often be separated by physical methods.
A pure substance has a fixed composition; mixtures may be uniform or non-uniform.
Original practice questions
Try each question first. Open the answer to check your reasoning.
Is water an element or compound?
Answer: A compound of hydrogen and oxygen.
Give a method to separate sand from water.
Answer: Filtration.
Is salt dissolved in water a mixture?
Answer: Yes; it is a solution (a homogeneous mixture).
Chapter summary
Classify materials by whether they contain one type of atom, chemically joined elements, or substances physically mixed together. The key ideas above give you a short revision path; practise explaining them in your own words and revisit any step you could not justify.