SC8 Q2W4D1: Pure Substances & Elements

🎯 Learning Goals

At the end of the lesson, the learners will be able to:

1. Identify the characteristics of pure substances by citing real-life examples with at least 3 correct distinctions between elements and compounds.
2. Differentiate elements and compounds using a classification table with at least 80% accuracy.
3. Explain the importance of classifying matter as pure substances in everyday contexts through a short written reflection with clear reasoning.

🧩 Key Ideas & Terms

• Pure Substance → matter with fixed composition and identical properties
• Element → substance made up of only one kind of atom
• Compound → substance formed by two or more different elements chemically combined
• Atom → smallest particle of an element that retains its identity

🔄 Prior Knowledge

Activity: Classify Everyday Substances

Show students common materials: oxygen gas, water, copper wire, salt. Ask: How many types of atoms are needed to form each substance?

Guide Questions:

1. Is oxygen made up of one kind of atom or more?
2. What about water — how many elements combine to form it?
3. Why is copper considered an element?
4. Why is salt considered a compound?

Show Answer

Oxygen → element (O)
Water → compound (H₂O)
Copper → element (Cu)
Salt → compound (NaCl)

📖 Explore the Lesson (Day 1 – Pure Substances: Elements and Compounds)

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🌍 1. Starting the Journey: What Makes Up Matter?

Every object you see, touch, or even breathe is made of matter. But matter is not just a random collection of particles—it can be classified. One of the most important classifications in science is whether matter is a pure substance or a mixture.

A pure substance is matter that has a definite and fixed composition. This means no matter where you find it, its composition will remain the same. For example:

• Pure water (H₂O) always contains 2 hydrogen atoms and 1 oxygen atom in every molecule.
• Salt (NaCl) always contains sodium and chlorine atoms in a fixed 1:1 ratio.

By contrast, mixtures like air, soil, or juice may change in composition depending on location or preparation.

Guiding Question: Why do scientists classify matter into pure substances and mixtures?

Show Answer

To organize and understand the properties of materials, predict how they behave in reactions, and identify whether they are suitable for specific uses (e.g., medicines require pure substances for safety).

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⚛️ 2. Elements: The Simplest Pure Substances

An element is the simplest form of matter that cannot be broken down by chemical means. Each element is made up of only one kind of atom.

Examples of elements in daily life:

• Oxygen (O₂): the gas we breathe
• Copper (Cu): used in electrical wires
• Gold (Au): used in jewelry
• Iron (Fe): used in construction and tools

Elements are represented by symbols on the Periodic Table of Elements. Each element has a unique atomic number, which represents the number of protons in its atoms.

Checkpoint: Look around you and list 3 objects. Identify one element in each object.

Show Answer

• Mobile phone → Copper (Cu) in wires
• Soda can → Aluminum (Al) in the can
• Ring → Gold (Au) or Silver (Ag)

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🧪 3. Compounds: When Elements Combine

A compound is formed when two or more different elements are chemically combined in fixed proportions.

Examples:

• Water (H₂O): hydrogen and oxygen
• Carbon dioxide (CO₂): carbon and oxygen
• Table salt (NaCl): sodium and chlorine
• Sugar (C₆H₁₂O₆): carbon, hydrogen, oxygen

Compounds often have properties very different from the elements that form them. Sodium (Na) is a reactive metal + Chlorine (Cl) is a poisonous gas → but together they form NaCl (edible salt).

Guiding Question: Why are the properties of compounds different from the elements that make them?

Show Answer

Because when atoms bond, they form new substances with new chemical properties, not just a mixture of the old ones.

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🔬 4. Comparing Elements and Compounds

Feature	Elements	Compounds
Composition	One kind of atom	Two or more different atoms
Simplest Unit	Atom	Molecule or formula unit
Separation	Cannot be broken down chemically	Can be broken down into elements by chemical means
Examples	O₂, Fe, Cu	H₂O, NaCl, CO₂

Mini-Task: Classify the following: Oxygen, Water, Copper, Salt.

Show Answer

• Oxygen → Element
• Water → Compound
• Copper → Element
• Salt → Compound

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🌐 5. Real-World Connections

• Healthcare: Medicines must use pure substances for correct dosage.
• Environment: Polluted water is not a pure substance; it contains mixtures of harmful compounds.
• Technology: Pure silicon (element) is used in computer chips.
• Daily life: Salt and sugar are compounds we consume daily.

Checkpoint: Why would it be dangerous if medicines were made of impure mixtures instead of pure compounds?

Show Answer

Because impurities can cause side effects, reduce effectiveness, or even be toxic.

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🧩 6. Guided Discovery Activity

Activity: Element or Compound Hunt

1. List 5 items around your house.
2. Identify whether each is mainly an element, compound, or mixture.
3. Share why you classified it that way.

Examples:

• Coin → element (copper, nickel)
• Sugar → compound (C₆H₁₂O₆)
• Air → mixture
• Water → compound
• Steel spoon → mixture (alloy of iron + carbon)

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⚡ 7. Deeper Thinking: Why This Matters

Classifying substances helps in:

• Predicting reactions: Knowing if a material is an element or compound helps predict how it reacts.
• Safety: Some elements are toxic (like mercury), but in compounds (like mercury sulfide), their properties change.
• Innovation: Scientists design new compounds (medicines, fertilizers, plastics) to improve life.

Reflection Prompt: Which pure substance (element or compound) do you think is the most important for human life? Why?

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📚 References

• Helmenstine, A. M. (2020). What are the elements in the human body? ThoughtCo. https://www.thoughtco.com/elements-in-the-human-body-p2-602188
• Silberberg, M. (2013). Chemistry: The molecular nature of matter and change. McGraw-Hill Education.
• Zumdahl, S. S., Zumdahl, S. A., & DeCoste, D. (2018). Chemistry (10th Ed.). Cengage Learning.
• Madriaga, E. (2015). Science links: Worktext for scientific and technological literacy. Rex Book Store Inc.

💡 Example in Action (Day 1 – Pure Substances: Elements & Compounds)

✨ Example 1: Oxygen Gas (O₂)

Description: Oxygen is made of only one type of atom (oxygen atoms).
Classification: Element, because it cannot be broken down into simpler substances.

Now You Try 1: Classify Nitrogen (N₂). Is it an element or a compound?

Show Answer

Nitrogen is an element. It is made of only one type of atom (N).

✨ Example 2: Water (H₂O)

Description: Water is made of hydrogen and oxygen atoms chemically combined.
Classification: Compound, because it has more than one kind of atom bonded in a fixed ratio.

Now You Try 2: Classify Carbon dioxide (CO₂).

Show Answer

Carbon dioxide is a compound made of carbon and oxygen atoms in a fixed ratio.

✨ Example 3: Copper Wire (Cu)

Description: Copper is made entirely of copper atoms.
Classification: Element.

Now You Try 3: Classify Gold (Au).

Show Answer

Gold is an element made of only gold atoms.

✨ Example 4: Table Salt (NaCl)

Description: Salt is made of sodium and chlorine atoms chemically combined.
Classification: Compound.

Now You Try 4: Classify Sugar (C₆H₁₂O₆).

Show Answer

Sugar is a compound made of carbon, hydrogen, and oxygen.

✨ Example 5: Helium Gas (He)

Description: Helium is made of only one kind of atom.
Classification: Element.

Now You Try 5: Classify Methane (CH₄).

Show Answer

Methane is a compound, made of carbon and hydrogen atoms.

📝 Try It Out (8 items)

Directions: Classify each substance as Element or Compound.

1. Iron (Fe)
2. Ammonia (NH₃)
3. Diamond (C)
4. Baking soda (NaHCO₃)
5. Hydrogen (H₂)
6. Table sugar (C₆H₁₂O₆)
7. Silver (Ag)
8. Water (H₂O)

Show Answer

1. Iron → Element
2. Ammonia → Compound
3. Diamond → Element (carbon)
4. Baking soda → Compound
5. Hydrogen → Element
6. Table sugar → Compound
7. Silver → Element
8. Water → Compound

✅ Check Yourself (15-item Mixed Quiz)

Directions: Answer the following questions.

🔹 Part A. Multiple Choice (1–5)

1. Which of the following is an element?
   a. H₂O   b. O₂   c. CO₂   d. NaCl
2. Which of the following best defines a compound?
   a. Made of only one type of atom   b. Cannot be separated chemically   c. Composed of two or more different atoms chemically bonded   d. Exists as a mixture of elements
3. Which property is true only for elements?
   a. Can form molecules   b. Cannot be chemically broken down   c. Always exist as gases   d. Always exist as liquids
4. Which of the following is a compound found in the human body?
   a. Carbon (C)   b. Oxygen (O₂)   c. Water (H₂O)   d. Gold (Au)
5. Which is the simplest unit of a compound?
   a. Atom   b. Proton   c. Molecule   d. Neutron

🔹 Part B. True or False (6–10)

6. An element can be broken down into simpler substances.
7. Salt (NaCl) is an example of a compound.
8. All compounds are also molecules.
9. Copper (Cu) is an example of a pure substance.
10. The ratio of atoms in a compound is always fixed.

🔹 Part C. Short Answer (11–15)

11. Give one real-life example of an element and where it is used.
12. Give one real-life example of a compound and its importance.
13. Differentiate between an element and a compound in one sentence.
14. Which pure substance (element or compound) do you use most often at home? Explain why.
15. Why do scientists need to classify matter into elements and compounds?

Show Answer Key

Part A
1. b    2. c    3. b    4. c    5. c

Part B
6. F    7. T    8. F    9. T    10. T

Part C (Sample Answers)
11. Iron (Fe) – used in construction
12. Water (H₂O) – essential for life
13. An element is made of one kind of atom; a compound is made of two or more atoms chemically bonded.
14. Answers may vary (e.g., salt, sugar, water)
15. To better understand matter, predict reactions, and use substances safely.

🚀 Go Further (Day 1 – Pure Substances: Elements & Compounds)

Directions: Choose at least one activity to complete.

1. Element Collage 🎨
   Collect pictures (from magazines, internet, or drawings) of 5 elements used in daily life. Label each with its symbol and use.
   Example

   Copper (Cu) → electrical wires; Oxygen (O₂) → breathing; Gold (Au) → jewelry; Iron (Fe) → construction; Helium (He) → balloons.
2. Compound Detective 🔍
   Look at product labels at home (shampoo, toothpaste, food packages). Identify 3 compounds listed as “active ingredients.” Classify each as covalent or ionic.
   Example

   NaF (toothpaste) → ionic; H₂O (water) → covalent; C₆H₁₂O₆ (sugar) → covalent.
3. Periodic Table Hunt 📊
   Pick 5 elements from the periodic table. Write their symbol, atomic number, and one real-world use.
   Example

   • H (1) → used in fuel cells
   • O (8) → respiration
   • Fe (26) → steel production
   • Si (14) → electronics
   • Na (11) → table salt
4. Daily Life Reflection ✍️
   Write a 1-paragraph reflection: “How would life be different if only elements existed, and no compounds were possible?”
   Sample Idea

   Life would not exist, since compounds like water and proteins are necessary for organisms. Our world would be made of isolated elements without the complexity needed for living systems.
5. Molecule Models 🧩
   Using clay, beads, or paper cutouts, build simple models of H₂O, O₂, and NaCl. Take note of whether each is an element or compound.
   Classification

   H₂O → compound; O₂ → element; NaCl → compound.

🔗 My Reflection

❓ Guiding Questions

Answer in your notebook:

1. What is one new idea I learned about pure substances today?
2. How can I apply my knowledge of elements and compounds in real life?
3. Which part of the lesson was most challenging for me?
4. How can I improve my understanding of pure substances?

✅ Reflection Checklist

Put a ✔️ mark for the items you agree with:

• I can explain the difference between elements and compounds.
• I can give at least 3 examples of elements and compounds from daily life.
• I understand why compounds have different properties from their elements.
• I can classify a given substance as an element or a compound.
• I can explain why classifying matter is important in science.