Elements, Compounds, and Molecules
What is the smallest unit of matter that keeps the properties of an element?
Atom
In which state of matter do particles vibrate in place?
Solid
What phase change occurs when water boils?
Evaporation – liquid to gas
Is melting ice physical or chemical? Why?
Physical; it’s still water, just a different state
What everyday process is an example of evaporation?
Water puddles drying up in the sun
Why is CaCO₃ a compound and not an element?
It has more than one type of element – calcium, carbon, and oxygen.
What happens to particle speed when temperature increases?
Particles move faster
When dry ice disappears, what type of phase change is happening?
Sublimation – solid to gas
Which of these is a chemical change: burning wood, breaking glass, melting butter?
Burning wood
Why does fog form on a bathroom mirror after a shower?
Water vapor condenses as it cools
All compounds are molecules, but not all molecules are compounds. Give one example of a molecule that is not a compound.
Examples: O₂, N₂, etc.
A block of iron is melted. How are its particles affected?
They move more rapidly and have more energy
Candle wax near the flame melts. What happens to the wax molecules to cause this?
Heat increases their kinetic energy, breaking them out of solid structure
Name two clues that a chemical change has occurred.
Gas produced, color change, temperature change, odor change, new solid formed
Why does the liquid inside a thermometer rise when heated?
Molecules expand as they move faster
Choose the two compounds: Neon (Ne), Ozone (O₃), Water (H₂O), Nitrogen (N₂), Ammonia (NH₃).
Water and Ammonia
Place these in order of increasing motion: ice cube, water, steam.
Ice cube → Water → Steam
Which phase change is occurring in this example: water droplets form on a bathroom mirror?
Condensation – gas to liquid
A student heats salt, oil, butter, and water. Which conclusion is best?
Heating and cooling affect different materials in different ways
Why is carbon especially important for living organisms?
It can form a wide variety of molecules essential for life
Explain why compounds cannot be separated by physical means and describe one way they can be separated.
They are chemically bonded; they can only be separated by chemical reactions.
A student sees liquid in a thermometer rise when moved from ice water to warm water. Explain why this happens.
Molecules in the liquid absorb heat, move faster, spread apart, and expand.
Explain how adding heat and removing heat affect particle motion during melting and freezing.
Adding heat → particles gain kinetic energy, move faster, break out of solid; Removing heat → particles lose kinetic energy, slow down, lock into solid structure
Explain why baking a cake is a chemical change, not a physical one.
New substances with different properties are formed – can’t reverse it
Describe how heat transfer from the environment affects both puddle evaporation and ice melting outside.
Heat is absorbed; in puddles → particles move faster and become gas; in ice → particles move faster, breaking free into liquid form