Compounds, Formulas, and Chemical Classification
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Compounds, Formulas, and Chemical Classification
Year 9 Science Understanding Chemical Bonds and Formulas Western Australian Curriculum
What Are Compounds?
Two or more different atoms chemically bonded together Have different properties from their constituent elements Examples: Water (H₂O), Salt (NaCl), Carbon dioxide (CO₂) Cannot be separated by physical means
Demonstration: Sodium + Chlorine = Salt
Sodium (Na): Soft, reactive metal Chlorine (Cl): Toxic yellow-green gas Sodium Chloride (NaCl): Safe table salt Properties completely change when elements combine!
Ionic vs Covalent Compounds
{"left":"Metal + Non-metal\nElectrons transferred\nForm crystals\nExamples: NaCl, MgO","right":"Non-metal + Non-metal\nElectrons shared\nForm molecules\nExamples: H₂O, CO₂"}
Reading Chemical Formulas
Chemical symbols represent elements Subscript numbers show how many atoms H₂O = 2 hydrogen atoms + 1 oxygen atom CO₂ = 1 carbon atom + 2 oxygen atoms
Formula Detective Challenge
NH₃: How many atoms total? CaCl₂: Which elements are present? CH₄: What type of compound? Work in pairs to solve these formula puzzles!
Think-Pair-Share
Why do you think compounds have different properties than their elements? Discuss with your partner Consider the bonding and structure changes
Success Check & Next Steps
Can you define a compound? Can you read chemical formulas and count atoms? Can you identify ionic vs covalent compounds? Next: We'll explore naming compounds and their real-world applications