CH 1 & 2: General Chemistry I: Properties of Matter, Mixtures, and Atomic Theory

Properties and Changes of Matter

Classification of Matter

All matter (anything that has mass and occupies space) can be classified by its state and its properties. The three primary states of matter are:

• Solid: Definite shape and volume; particles are closely packed in a fixed arrangement.

• Liquid: Definite volume but no definite shape; particles are close together but can move past one another.

• Gas: No definite shape or volume; particles are far apart and move freely.

Example: Ice (solid), water (liquid), and steam (gas) are all forms of H2O.

Physical and Chemical Properties

• Physical property: A property of matter that can be measured without changing the identity and composition of the substance. Example: Melting point, boiling point, density, color.

• Chemical property: Describes the way a substance may change or react to form other substances. Example: Flammability, reactivity with acids, ability to rust.

By classifying the properties of matter, we can also classify the changes in matter as physical or chemical.

Physical vs. Chemical Changes

• Physical change: A change that alters the physical form of a substance without changing its chemical identity. Example: Boiling water (liquid to gas), dissolving sugar in water.

• Chemical change: A change that results in the formation of one or more new substances with different chemical properties. Example: Burning wood, rusting of iron.

Concept Check Example: Boiling water is a physical change; the formation of water from hydrogen and oxygen gases is a chemical change.

Pure Substances and Mixtures

Definitions

• Pure substance: Has a constant composition and a fixed set of physical and chemical properties. Examples: Water (H2O), sodium chloride (NaCl).

• Mixture: A combination of two or more substances in which each substance retains its own chemical identity and properties. Mixtures can be physically separated into their components.

Types of Mixtures

• Homogeneous mixture (solution): Uniform composition throughout; components are not visibly distinguishable. Examples: Saltwater, air.

• Heterogeneous mixture: Non-uniform composition; components are visibly distinguishable. Examples: Sand in water, salad.

Question: Can a solid or gas be a solution? Yes, alloys (solid solutions) and air (gaseous solution) are examples.

Separation of Mixtures

• Physical methods such as filtration, distillation, and chromatography can be used to separate mixtures based on differences in physical properties.

Modern Atomic Theory

Fundamental Laws

• Law of Conservation of Mass: In a chemical reaction, matter is neither created nor destroyed. Equation: $\text{Total mass of reactants} = \text{Total mass of products}$

• Law of Definite Proportions: All samples of a given compound have the same proportions of their constituent elements. Example: Water always contains hydrogen and oxygen in a 2:1 ratio by atom count.

Dalton's Atomic Theory

1. All matter is composed of indivisible atoms. An atom is an extremely small particle of matter that retains its identity during chemical reactions.

2. An element is a type of matter composed of only one kind of atom; each atom has the same properties.

3. A compound is a type of matter composed of atoms of two or more elements chemically combined in fixed proportions.

4. A chemical reaction consists of the rearrangement of the atoms present in the reacting substances to give new chemical combinations present in the substances formed by the reaction.

Discussion: Some aspects of Dalton's theory have been revised (e.g., atoms are divisible into subatomic particles, and isotopes exist), but the core ideas remain foundational.

Additional Information and Study Tips

• Be familiar with SI units and prefixes (from mega to pico) and common derived units.

• Understand reliability of measurement, significant figures, and calculations involving significant figures, precision, and accuracy.

• Know atomic structure basics: electrons, protons, neutrons, mass number, atomic number, and isotopes.

Additional info: For more details on measurement and atomic structure, refer to textbook sections on SI units, significant figures, and atomic models.