Chemistry Essentials: Mixtures and the Periodic Table

Unit 1: Matter and Mixtures

Mixtures are combinations of two or more substances that are not chemically combined. They keep their physical properties and can be separated by physical means.

Homogeneous and Heterogeneous Mixtures

• Homogeneous Mixtures: These are uniform throughout. Components cannot be seen, and they cannot be filtered.
  • Solutions: Evenly distributed liquids that do not filter; substances are dissolved (e.g., salt and water).
  • Alloys: Two or more elements where at least one is a metal; these can be separated but not by simple physical means.
  • Colloids: These can be separated (e.g., mayonnaise or gelatin).
• Heterogeneous Mixtures: These are non-uniform. Components can be seen.
  • Suspensions: These can be filtered as large particles are visible and do not dissolve (e.g., orange juice).

Methods for Separating Mixtures

• Filtration: Separation by particle size (not for solutions). This is used to separate heterogeneous mixtures of solids and liquids.
• Sifting: Separation by particle size (used only for solids).
• Magnetic Separation: Separates materials that are drawn to a magnetic field.
• Evaporation: Heating a solution causes water to evaporate, leaving the other part of the mixture behind.
• Crystallization: Separation by solubility. It relies on compounds forming crystals as they cool. It is the formation of pure solid particles from a solution.
• Extraction: Separates liquids by densities (for liquids that do not dissolve into each other).
• Distillation: Separates mixtures of liquids based on the boiling points of the components.
• Centrifugation: Separates components by density.

Pure Substances: Elements and Compounds

A substance is any matter that is not a mixture. It is pure matter with a definite and constant composition, making it difficult or impossible to break apart.

• Elements: The simplest form of matter, made entirely from one type of atom. Atoms make up elements, and they cannot be broken down further.
• Compounds: These have different characteristics than the elements they are made of and can be separated by chemical means.

Physical and Chemical Properties

Physical Properties are observed using the five senses (e.g., temperature, texture, luster, color, and odor).

• Solubility: Calculated as the mass of solute divided by the volume of solvent (e.g., salt dissolving in water or ripping a piece of paper).
• Metals and Non-metals: Physical properties include hardness for metals and malleability.

Chemical Properties include flammability, combustion, reactivity, oxidation, toxicity, and radioactivity (e.g., paper burning or food decomposing). Indicators of chemical change include changes in color, odor, temperature, or the formation of bubbles.

Unit 2: Atomic Structure and the Periodic Table

Valence Electrons and Shells

• Valence Electrons: Increase from left to right across the table.
• Valence Shells: Increase from top to bottom down the table.

The Periodic Table of Elements

Why do elements in the same group have similar properties? It is because they have the same number of valence electrons.

• Dmitri Mendeleev: The scientist responsible for the organization of the periodic table.
• Mercury: The only metal that exists as a liquid at room temperature.
• Bromine: The only non-metal that exists as a liquid at room temperature.
• Conductivity: A physical property of all metals is that they are good conductors of heat.
• Elements: There are 92 naturally occurring elements.
• Man-made Elements: An example is Neptunium.