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🔬 Science - Class 7
Unit 9 · Matter

Molecules and Compounds Presentation

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Unit 9 · Matter

Molecules and Compounds

Science & Technology · Grade 7

Learning Objectives

🔗

Define a molecule and tell it apart from an atom

💧

Say what atoms are in H₂O, and in what numbers

🧂

Define a compound and explain why it has new properties

🔤

Explain how so few elements make so many substances

Same Atoms, or Different Atoms?

  • A molecule is two or more atoms joined chemically
  • All the same kind: a molecule of an ELEMENT. H₂, O₂, Cl₂
  • More than one kind: a molecule of a COMPOUND. H₂O, HCl
  • One question sorts every molecule you will ever meet
On the left, two H circles joined, two O circles joined and two Cl circles joined. On the right, two H joined to one O, and one H joined to one Cl

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Presenter notes: Write two things on the board: a metal that catches fire when it touches water, and a green gas once used as a poison. Ask what you would get if you put those two together, and let the class predict something dreadful. Then tell them the answer is the salt in the pot in their own kitchen, and let the disbelief sit for a moment. Say that today is about what happens when atoms join, and that the most surprising thing in the whole unit is that a compound behaves nothing at all like the things it was made from.