Fundamental Concepts in Chemistry: Matter, Mixtures & Atomic Principles

Understanding Substances and Mixtures

Substances are formed by identical particles, which can be either atoms or molecules. Within the realm of substances, we distinguish between:

• Elements: Pure substances that cannot be decomposed into simpler substances by chemical means.
• Compounds: Substances whose molecules are formed by two or more different elements chemically bonded together.

Mixtures: Combinations of two or more substances that are not chemically bonded.

Types of Mixtures

• Homogeneous Mixtures: Mixtures where components are uniformly distributed and indistinguishable, appearing as a single phase.
• Heterogeneous Mixtures: Mixtures where components are not uniformly distributed and are visibly distinct, appearing as multiple phases.

Mixtures can always be separated by physical methods.

Methods for Separating Mixtures

Mechanical Separation Techniques

• Sedimentation: A process where suspended solid particles settle to the bottom of a liquid due to gravity, allowing the separation of layers.
• Decantation: A process similar to sedimentation, used to separate immiscible liquids or a liquid from a settled solid by carefully pouring off the top layer.
• Centrifugation: A method that uses a centrifuge, a device that rotates at high speed, to separate components of a mixture based on density by applying centrifugal force.
• Elutriation: A method of separation by density where a fluid stream carries lighter particles away from heavier ones.
• Filtration: A method to separate insoluble solid particles from a liquid or gas by passing the mixture through a porous medium (filter) that retains the solids.
• Magnetic Separation: Used to separate magnetic materials from non-magnetic ones, often employed in mining to extract magnetic ores.

Phase Change Separation Techniques

• Crystallization: The process of forming solid crystals from a solution, often by evaporating the solvent, as seen in obtaining sea salts from seawater.
• Evaporation to Dryness: A method where a solution is heated in a crucible to completely remove the solvent, leaving the solid solute behind, especially when crystal size is not a concern.
• Distillation: A separation technique that involves heating a liquid mixture to create vapor, then cooling the vapor to condense it back into liquid, separating components based on their different boiling points.

Solutions and Concentration

Solutions are stable, homogeneous mixtures.

• Solute: The substance present in a smaller proportion within a solution, often the one that changes its physical state during dissolution.
• Solvent: The component present in a greater proportion in a solution, usually the one that retains its physical state during dissolution.

Solubility: The maximum amount of a substance (solute) that can dissolve in a given amount of solvent (e.g., 100 g of water) at a specific temperature.

Types of Solutions by Concentration

• Diluted Solution: Contains a very small amount of solute compared to its solubility limit.
• Concentrated Solution: Contains a significant amount of solute, approaching its solubility limit.
• Saturated Solution: Contains the maximum amount of solute that can be dissolved at a given temperature; no more solute can dissolve.

Concentration Calculations

• Percentage Mass (% Mass): (mass of solute (g) / mass of solution (g)) × 100%
• Percentage Volume (% Volume): (volume of solute (cm³) / volume of solution (cm³)) × 100%
• Mass Concentration (g/L): mass of solute (g) / volume of solution (L)

Coulomb's Law

Coulomb's Law: Describes the electrostatic force (F) between two charged particles (q₁ and q₂), separated by a distance (d), where K is Coulomb's constant. The formula is:

F = K • q₁ • q₂ / d²

Atomic Structure Fundamentals

• Atomic Number (Z): Represents the number of protons in an atom's nucleus.
• Mass Number (A): The total number of protons and neutrons in an atom's nucleus.
• In a neutral atom, the Number of Protons = Number of Electrons.