Science Class: Observations and Substance Properties

Qualitative and Quantitative Observations

• Qualitative observations use our senses to describe something.
• Quantitative observations use numbers and measurements.

Inferring and Classifying

• Inferring is drawing conclusions based on evidence.
• Classifying is grouping objects based on similarities, differences, and relationships.

Measuring

• Measuring uses numbers and involves two parts: magnitude and unit.

Observing

• We use our senses to observe objects.

Communicating

• We communicate observations and findings to inform others.

Pure Substances

• A pure substance consists of only one type of substance or particle.
• Pure substances cannot be separated by physical means.
• Examples: salt, hydrogen gas, gold metal, copper wire, diamonds.

Mixtures

• Mixtures are formed by physically combining two or more substances.

Properties of Pure Substances

• Boiling Point: Pure substances have a constant and lower boiling point.
• Melting/Freezing Point: Pure substances have a constant and higher melting/freezing point.

Elements

• Elements cannot be broken down into simpler substances.
• The periodic table contains 118 elements.
• 90 elements occur naturally, while 28 are created in labs.
• Elements have chemical symbols, usually one or two letters.
• Symbols can be capital letters or a capital letter followed by a small letter.
• Elements have English or Latin names.

Classification of Elements

• Metals: hard, shiny (lustrous), malleable (thin sheets), ductile (thin wire), good conductors of heat and electricity, extracted from ores.
• Nonmetals: mostly gases at room temperature, dull, brittle, poor conductors of heat and electricity.
• Metalloids: have properties of both metals and nonmetals.

Compounds

• Compounds are formed by chemically combining two or more elements or molecules.
• They have a fixed ratio or composition.
• Compounds are represented by chemical names or formulas.

Molecules

• Molecules are formed by chemically combining two or more atoms.
• Molecules are the smallest particle of a compound.

Classifying Compounds

• Organic Compounds: contain hydrogen and carbon atoms bonded together.
  • Carbohydrates
  • Lipids
  • Proteins
  • Nucleic acids
• Inorganic Compounds: do not contain hydrogen and carbon.
  • Examples: salt, soap, toothpaste.

Mixtures

• Heterogeneous Mixtures: particles are not evenly spread, sizes vary, and components are easily identified.
  • Suspension: Particles are large enough to be seen by the naked eye.
  • Colloids: Particles do not settle at the bottom.
  • Coarse: Particles can be easily recognized and picked apart by hand.

Properties of Solutions

• Solutions are formed by combining two or more substances.
• Solute + Solvent = Solution
• Solutions appear to be in one phase.

Solute, Solvent, and Dissolution

• Solute: The substance that dissolves in a solvent. The amount of solute affects concentration.
• Solvent: The substance that dissolves the solute. It is usually a liquid.
• Dissolution: The process of making a solution.

Soluble/Insoluble and Miscible/Immiscible

• Soluble/Insoluble: Refers to the dissolving ability of a substance in a specific amount.
• Miscible/Immiscible: Refers to the ability of substances to mix in any amount.

Unsaturated, Saturated, and Supersaturated Solutions

• Unsaturated Solution: More solute can be dissolved.
• Saturated Solution: No more solute can be dissolved.
• Supersaturated Solution: Excess solute cannot be dissolved, requiring additional solvent or heat to dissolve.

Factors Affecting Solubility

• Temperature: Solubility varies with temperature.
• Surface Area: Grinding solids into smaller pieces increases surface area, increasing solubility.
• Stirring: Speeding up the dissolution process.
• Pressure: Higher pressure increases the amount of gas dissolved in a liquid.
• Nature of Solute and Solvent: Inherent chemical properties of the substances being mixed.