Chapter 1

Chemistry- The Central Science

Scientific Method

A systematic approach to experimentation in science.

Observations

Natural phenomena and measured events that can be stated as a law if universally consistent.

Hypothesis

A tentative explanation that accounts for observations.

Experiment

A procedure to test a hypothesis by measuring one variable at a time.

Model (Theory)

A set of conceptual assumptions that explains data from experiments and predicts related phenomena.

Chemistry

The study of matter and the changes that matter undergoes.

Matter

Anything that has mass and occupies space.

Substance

A form of matter with a specific composition and distinct properties; can be elements or compounds.

Mixture

A combination of two or more substances where the substances retain their distinct identities.

Element

A substance that cannot be separated into simpler substances by chemical means.

Compound

A substance composed of atoms of two or more elements chemically united in fixed proportions.

Constituent Elements

The elements that make up a compound, which cannot be separated by physical means.

Quantitative Properties

Properties that can be measured and expressed with numbers.

Qualitative Properties

Properties that do not require explicit measurement.

International System of Units (SI Units)

Standard units used for measurements in science.

Derived Units

Units derived from combining base units, such as volume and density.

Homogeneous Mixture

A mixture with a uniform composition throughout.

Heterogeneous Mixture

A mixture with variable composition where substances remain distinct.

Physical Property

A property that can be observed and measured without changing the identity of the substance.

Physical Change

A change in which the state of matter changes but the identity of matter does not.

Exact Numbers

Defined values or counted numbers that have no uncertainty.

Inexact Numbers

Measured values that include uncertainty.

Significant Figures (SigFigs)

Digits used to indicate the uncertainty in measured values.

Uncertain Digit

The last digit in a measured value, representing uncertainty.

Chemical Property

A property that can only be studied by converting the substance into another substance.

Chemical Change

A process in which one or more substances are transformed into new substances.

Extensive Properties

Properties that depend on the amount of matter, such as mass.

Intensive Properties

Properties that do not depend on the amount of matter, such as density.

Conversion Factor

A fraction that expresses the same quantity in different units.

Dimensional Analysis (Factor-Label Method)

A method of problem-solving that uses conversion factors to convert units.

Accuracy

How close measured values are to the true value.

Precision

How close multiple measured values are to each other.