Chemistry: Pure Substances vs Mixtures

Study Notes

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.

Description

Test your knowledge on the differences between pure substances and mixtures in chemistry. This quiz covers elements, compounds, and the characteristics of homogeneous and heterogeneous mixtures. Challenge yourself to identify key concepts related to the classification of materials.