Chemistry: Pure Substances vs Mixtures

Pure Substances vs. Mixtures

• Pure Substances: Composed of one type of particle, can be elements or compounds.
• Elements: Made up of only one type of atom (examples: gold, oxygen).
• Compounds: Formed from two or more types of atoms chemically bonded (example: water H₂O).
• Mixtures: Contains two or more substances physically combined, not chemically bonded.
• Homogeneous Mixtures: Uniform composition; components are evenly distributed (example: saltwater).
• Heterogeneous Mixtures: Non-uniform composition; components are distinct (example: salad).

Atoms, Molecules, Elements, and Compounds

• Atom: The fundamental unit of matter, retains chemical properties.
• Molecule: Two or more atoms bonded together (examples: O₂, H₂O).
• Element: Comprised solely of one type of atom (examples: helium, carbon).
• Compound: Two or more types of atoms chemically combined (examples: NaCl, CO₂).

Particle Theory

• Phase Changes: Matter transitions between solid, liquid, and gas due to energy changes (heat).
• Melting: Solid to liquid.
• Evaporation: Liquid to gas.
• Condensation: Gas to liquid.
• Freezing: Liquid to solid.
• Expansion: Increased temperature causes particles to move faster and spread apart.
• Diffusion: Movement of particles from high to low concentration.

Density

• Density Formula: Density = Mass / Volume
• Density Units:
  • Liquids: g/mL
  • Solids: g/cm³
• Example: A material with mass 10g and volume 5cm³ has a density of 2g/cm³.

Properties of Solid, Liquid, and Gas

• Solid: Particles are tightly packed with a definite shape and volume.
• Liquid: Particles are closely packed but can move; definite volume but no fixed shape.
• Gas: Particles are widely spaced, moving freely; neither definite shape nor volume.

Chemical vs. Physical Changes

• Physical Change: Alters state or appearance without changing the substance (examples: melting, freezing).
• Chemical Change: Forms new substances with different chemical properties (examples: burning, rusting).

Rates of Reaction

• Temperature: Higher temperatures boost particle energy, elevating reaction rates.
• Concentration: Increasing reactant concentration leads to more collisions.
• Surface Area: Smaller particles enhance surface area, boosting reaction speed.
• Catalysts: Speed up reactions without being consumed in the process.
• Pressure: For gases, increased pressure brings particles closer, resulting in more collisions.

Model of Atoms

• Protons: Positively charged particles found in the nucleus.
• Neutrons: Neutral particles also located in the nucleus.
• Electrons: Negatively charged particles orbiting the nucleus.
• Atomic Number: Total number of protons in an atom.
• Mass Number: Total count of protons and neutrons in an atom.

Formulas of Atoms and Molecules

• Atoms: Denoted by elemental symbols (example: C for Carbon).
• Molecules: Represented by atomic symbols with subscripts indicating number of atoms (example: H₂O for water).

Periodic Table Names and Symbols

• Elemental Symbols: Represent elements using one or two letters (examples:
  • C for Carbon
  • N for Nitrogen
  • Na for Sodium
  • O for Oxygen)
• Chemical Formulas:
  • H₂O: Water (2 Hydrogen + 1 Oxygen)
  • H₂: Hydrogen gas (2 Hydrogen atoms)
  • CO₂: Carbon Dioxide (1 Carbon + 2 Oxygen atoms)

Chemical Equations

• Representation: Illustrate chemical reactions with reactants transitioning into products.
• Example Equation: 2H₂ + O₂ → 2H₂O
• Balancing: Ensures equal numbers of each atom on both sides of the equation for conservation of mass.