Chemistry: Pure Substances and Mixtures

Pure Substances and Mixtures

• Pure Substances: Composed of a single type of particle; have consistent properties throughout (e.g., elements and compounds).
• Mixtures: Combinations of two or more pure substances; properties can vary throughout the mixture.

Classification of Elements

• Metals: Typically solid (except mercury), good conductors of heat and electricity, and malleable. Examples include iron, copper, and gold.
• Non-Metals: Can be solid, liquid, or gas; poor conductors and often brittle. Examples are oxygen, sulfur, and bromine.
• Metalloids: Exhibit properties intermediate between metals and non-metals; semiconductors are important in electronics. Examples include silicon and arsenic.

Types of Compounds

• Acids: Substances that release hydrogen ions (H⁺) in solution; characterized by a sour taste and can conduct electricity. Examples include hydrochloric acid and sulfuric acid.
• Bases: Substances that release hydroxide ions (OH⁻) in solution; have a bitter taste and slippery feel. Common bases include sodium hydroxide and potassium hydroxide.

Homogeneous and Heterogeneous Mixtures

• Homogeneous Mixtures: Components are uniformly distributed; the mixture looks the same throughout and cannot be easily separated. Examples include saltwater and air.
• Heterogeneous Mixtures: Components can be seen and separated; the mixture has varying composition and properties. Examples include salad and sand.

Types of Mixtures

• Solutions: Mixtures where one substance is dissolved in another; they are homogeneous and transparent.
• Suspensions: Mixtures where particles are dispersed but not dissolved; they are heterogeneous and tend to settle over time. Examples include muddy water.
• Colloids: Mixtures with smaller particles that remain dispersed and do not settle; can appear homogeneous but scatter light. Examples include milk and fog.