Chemistry: The Central Science

Definition and Importance

Chemistry is the study and investigation of the structure and properties of matter. It is considered the central science because it connects and is integral to many other scientific disciplines, including biology, physics, environmental science, geology, astronomy, and medicine.

• Matter: Anything that has mass and occupies space. All chemicals are made up of matter.

• Macroscopic: Objects or substances large enough to be seen with the naked eye (e.g., keys, oceans, textbooks, planets, people).

• Microscopic: Objects or substances too small to be seen without magnification (e.g., atoms, molecules).

Additional info: Chemistry helps explain the composition, structure, and changes of matter, making it foundational for understanding the natural world.

Atoms, Molecules, and Chemical Compounds

Basic Building Blocks

• Atoms: The simplest form of matter; the basic units that make up elements.

• Molecules: Combinations of two or more atoms bonded together (e.g., H2O).

• Chemical Compounds: Substances composed of two or more different elements chemically bonded (e.g., SiO2).

Everything in the macroscopic world is made up of microscopic components—atoms and molecules. Chemistry studies both the visible and invisible aspects of matter.

The Periodic Table

The periodic table is an organized collection of all known elements (atoms). It provides both qualitative and quantitative information about each element.

• Students are responsible for knowing the names and symbols for elements #1-57, 72-89, 92, and 94.

The Scientific Method

Process of Scientific Inquiry

The scientific method is a systematic procedure for processing and understanding certain types of information. It is fundamental to scientific investigation.

• Observation: Gathering information, often involving measurement.

• Formulating a Hypothesis: Proposing a possible explanation for an observation.

• Experimentation: Testing the hypothesis through controlled experiments.

• Theory (Model Formation): Developing a set of tested hypotheses that provide a general explanation for a phenomenon.

Key Terms

• Hypothesis: A possible explanation for an observation. It must be testable.

• Theory: A well-substantiated explanation of some aspect of the natural world, based on a body of evidence. Theories are dynamic and can change with new evidence.

• Law: A statement that summarizes what happens; a concise description of observed phenomena. Laws do not change often.

Example: The law of conservation of mass states that in a chemical reaction, matter is neither created nor destroyed.

Measurement in Chemistry

Quantitative Observations and SI Units

Quantitative observations consist of a number and a unit. The international system of units used in science is called the SI system.

From these seven primary units, many other units can be derived. For example, volume is derived from length: 1 cubic meter (1 m3) = 1,000,000 mL. 1 cm3 = 1 mL.

• 1 lb = 453.59 g

• 1 in = 2.54 cm

• 1 U.S. gallon = 3.785 L

Mass vs. Weight

• Mass: A measure of the amount of matter in an object. It is independent of location.

• Weight: A measure of force; depends on the gravitational pull on the object. Weight can change depending on location (e.g., Earth vs. Moon).

Formulas:

• Force:

• Weight:

On Earth, mass and weight are often used interchangeably, but they are not the same in scientific contexts.

Practice and Application

Sample Questions and Concepts

• As temperature increases, the molecules in a gas move farther apart.

• Order of the scientific method: Conducting experimental work, collecting observations, making a hypothesis, establishing a theory.

• Theories do not become laws; they serve different purposes in science.

• Common SI units for mass, length, and time: kilogram (kg), meter (m), second (s).

• 1 cm3 = 1 mL.

• A picometer is less than a micrometer.

Additional info: Mastery of SI units, scientific method, and the distinction between mass and weight is essential for success in general chemistry.