Pure Substances, Mixtures, and the Particle Theory of Matter: Grade 7 Science Dossier

Learning Shift: The Grade 7 science lessons change from looking at big physical properties to understanding tiny particles and how they work together.
Connected Learning: This module includes updates for Strand C (about Matter and Energy) along with important STEM skills and real-life examples found in Strand A.
Structure: The content is split into three parts, serving as a resource for teachers and curriculum developers.

What It Is: A model that helps us understand how matter behaves, even when we can't see it.
Six Key Ideas:
1. Tiny Parts: Everything is made up of tiny pieces called particles (atoms or molecules), not just one solid block.
  - Example: You can squeeze gas to make it take up less space.
2. Same Particles: All particles in one type of matter are the same, giving it consistent properties.
  - Example: Pure water always boils at $100^\text{C}$ .
3. Moving Particles: Particles are always moving around randomly unless they're at absolute zero.
  - Example: Food coloring spreads in still water.
4. Heat and Motion: Heat makes particles move faster due to added energy.
  - Example: A balloon inflates when taken from a cold place to a warm room.
5. Spaces Between Particles: There’s space between particles, and this varies depending on the state of matter.
  - Example: Sugar dissolving in water doesn’t make it overflow.
6. Forces Between Particles: Particles are attracted to each other, and how strong this attraction is depends on the substance.
  - Example: Diamonds are very strong, while orange juice flows freely.
Learning Shift: Students need to connect what they see to how particles are modeled. A temperature rise means particles are moving faster on average.
Experiment: Heating air in a bottle can push up a coin.

Pure Substances: Only one type of particle inside, with the same properties throughout.
- Elements: Simplest forms of matter made of one type of atom (e.g., gold, oxygen).
- Compounds: Two or more different elements that are mixed chemically (e.g., water $H_2O$ ).
Mixtures: Combinations of substances that keep their original properties.
- Heterogeneous Mixtures: Different components are visible (e.g., sand and water).
- Homogeneous Mixtures: Uniform appearance (e.g., salt in water).

How Dissolving Works: Dissolving is a physical change. The forces between the solute and solvent must be strong enough to break the solute's internal forces.
Water's Role: When salt (sodium chloride) dissolves in water, the water molecules surround and separate the salt particles.
Dissolving Rules:
- "Like dissolves like": Polar (water) dissolves polar/ionic substances (salt/sugar).
- Solubility Limit: The maximum solute that can dissolve in a certain amount at a set temperature.
Factors Influencing Dissolving Speed:
1. Temperature: Higher temperature boosts particle movement.
2. Stirring: Stirring helps mix solute particles with the solvent.
3. Size of Particles: Smaller particles dissolve faster because they have more surface area.

Types of Solutions:
- Unsaturated: Can dissolve more solute.
- Saturated: Can't dissolve any more solute, extra settles at the bottom.
- Supersaturated: More solute than usual is dissolved, forcing crystal formation when disturbed.
Steps of Dissolving:
1. Breaking the solute bond (needs energy).
2. Breaking the solvent bond (also needs energy).
3. Making new bonds between the solute and solvent (releases energy).
Gases in Solutions: Gases dissolve less in warmer liquids. Warmer water holds less oxygen, affecting fish.

Mineral Extraction:
- Mechanical Methods: Like crushing to expose more surface area.
- Gravity Methods: Using weight differences, like in gold panning.
- Magnetic Separation: Sorting metals in recycling.
- Chemical Methods: Using toxic chemicals (cyanide) to extract metals.
Air Separation: Uses cooling techniques to separate nitrogen, oxygen, and argon from air.
Oil Refining: Uses heating to separate crude oil into various useful products based on boiling points.
Water Treatment:
- Primary: Mechanical cleaning with screening.
- Secondary/Tertiary: Additional filtering and cleaning to remove bacteria.

E-Waste: Ontario produces a lot of electronic waste, which can be toxic.
- Common toxins include lead and mercury.
- Recycling: New laws shift recycling responsibility to producers and ensure high recycling targets.
Green Chemistry: Focus on reducing waste and using sustainable materials, with support from businesses for innovative solutions.

Heating Safety: Use hot plates instead of burners; hot plates can burn too but don’t look hot.
Glassware: Use specific type of glass for heating and check for cracks.
Spill Kits: Required for managing spills, using materials like cat litter for oil.
Safety Data Sheets: All chemicals must have clear safety information.
Learning Modules: Activities designed for understanding Matter, Solutions, and Separation, including cool experiments.