Introduction to General Chemistry: Matter, Scientific Method, and Properties

Introduction to Chemistry

What is Chemistry?

Chemistry is the scientific study of the composition, properties, and interactions of matter. Matter is defined as anything that has mass and occupies space. Chemicals are substances with a definite composition and set of properties, and they are present in everything around us.

• Matter: Anything with mass and volume.

• Chemicals: Substances with the same composition and properties throughout.

• Natural vs. Synthetic: Natural chemicals are found in nature without human intervention (e.g., caffeine, citric acid), while synthetic chemicals are human-made, often with altered properties (e.g., aspirin, plastics).

Additional info: The distinction between natural and synthetic does not imply safety or danger; both can be safe or hazardous depending on their properties and use.

Fields of Chemistry

Major Branches

• Inorganic Chemistry: Study of non-carbon-containing compounds.

• Organic Chemistry: Study of carbon-containing compounds.

• Analytical Chemistry: Characterization and analysis of matter's composition.

• Biological Chemistry (Biochemistry): Chemical processes in living organisms.

• Physical Chemistry: Principles of physics applied to chemical systems and interactions.

Additional info: Chemistry is interconnected with fields such as medicine, biology, environmental science, materials science, and more.

The Scientific Method

Steps and Definitions

• Observation: Gathering information using senses or tools. Can be qualitative (descriptive) or quantitative (numerical).

• Hypothesis: A testable statement proposed to explain observations. Must be falsifiable.

• Experiment: Controlled procedure to test a hypothesis. Generates data to accept or reject the hypothesis.

• Scientific Law: A statement based on repeated observations that describes what nature does (e.g., Law of Conservation of Mass: Matter is not created nor destroyed in a chemical reaction).

• Scientific Theory: An explanation for observations, supported by extensive evidence, that describes why or how nature behaves as it does (e.g., Atomic Theory).

Example: If both cans of soda are placed in water, the diet soda floats because it is less dense—a hypothesis that can be tested experimentally.

Classifying Matter

By State

• Solid: Particles are tightly packed in a fixed pattern; definite shape and volume; particles vibrate in place.

• Liquid: Particles are close but not fixed; definite volume but no definite shape; particles slide past each other.

• Gas: Particles are far apart and move rapidly; no definite shape or volume; fills container and can be compressed.

• Plasma: Like a gas, but particles are ionized (charged); conducts electricity; found in stars and neon signs.

By Composition

• Pure Substance: Composed of one type of matter; same properties throughout. Can be an element or a compound.

• Mixture: Composed of two or more types of matter; properties can vary between samples. Can be separated by physical means.

Types of Pure Substances and Mixtures

• Element: Cannot be broken down by chemical means (e.g., Au, O2).

• Compound: Two or more elements chemically combined (e.g., H2O, NaCl).

• Homogeneous Mixture (Solution): Uniform composition throughout (e.g., air, saltwater).

• Heterogeneous Mixture: Variable composition; different parts have different properties (e.g., oil and water, salad).

Physical and Chemical Properties and Changes

Physical Properties

Characteristics that can be observed or measured without changing the substance's chemical identity.

• Examples: shape, odor, mass, volume, density, boiling/melting points, electrical conductivity.

Physical Changes

Changes in state or appearance that do not alter the chemical identity of the substance.

• Examples: melting, freezing, dissolving, subliming, separating mixtures.

Chemical Properties

Characteristics that can only be observed by changing the chemical identity of a substance.

• Examples: flammability, acidity, toxicity, reactivity, corrosiveness.

Chemical Changes

Changes that result in the formation of new substances with different properties; atoms are rearranged.

• Examples: rusting, combustion, digestion, dye fading.

Tables and Diagrams

Classification of Matter by Composition

Type	Definition	Examples
Element	Cannot be broken down by chemical means	Gold (Au), Oxygen (O2)
Compound	Two or more elements chemically combined	Water (H2O), Sodium chloride (NaCl)
Homogeneous Mixture	Uniform composition throughout	Saltwater, air
Heterogeneous Mixture	Variable composition	Oil and water, salad

Key Equations

• Law of Conservation of Mass:

$\text{Total mass of reactants} = \text{Total mass of products}$

Examples and Applications

• Physical Change Example: Ice melting to water (no new substance formed).

• Chemical Change Example: Iron rusting (iron reacts with oxygen to form iron oxide).

• Mixture Example: Air (homogeneous mixture of gases).

• Compound Example: Table salt (NaCl), composed of sodium and chlorine atoms chemically bonded.

Review Questions

1. What is matter? Give two properties that define it.

2. Name one of the five major fields of chemistry.

3. Describe the difference between a qualitative and a quantitative measurement.

4. Classify the following as a physical or chemical change: burning wood, freezing water, digesting food.

5. Identify each of the following as an element, compound, homogeneous mixture, or heterogeneous mixture: air, brass, cookie, oxygen, carbon monoxide.