chem

Science

Knowledge gained through experience or experimentation; both an activity and the result of that activity.

Chemistry

The study of matter and its interactions with other matter and energy.

Hypothesis

A possible explanation for an event.

Law

A statement summarizing a large number of observations without explaining why.

Theory

An explanation of the laws of nature, explaining why the law is observed.

Matter

Anything that has mass and occupies space.

Mass

The quantity of matter in an object.

Weight

The force of attraction between an object and other objects, influenced by gravity.

Extensive properties

Properties that depend on the size of the sample, such as mass and volume.

Intensive properties

Properties that are independent of the sample size, such as density and color.

Physical property

A property that can be measured without changing the composition of the sample.

Chemical property

Describes the reactivity of a material.

Physical change

Occurs without changing the composition of the material.

Chemical change

Involves at least part of the material transforming into a different kind of matter.

Substance

Chemically the same throughout, can be an element or a compound.

Mixture

A combination of two or more substances that can be separated by physical methods.

Homogeneous mixture

Has a uniform composition throughout, also called a solution.

Heterogeneous mixture

Composition varies, such as rocks.

Accuracy

The agreement of a set of measurements with the true value.

Precision

The agreement among repeated measurements of the same quantity.

Significant figures

Includes all digits from the first non-zero digit to the last reported digit, indicating precision.

SI Units

The standard for measurements in science, including meter, kilogram, and second.

Atomic number (Z)

The number of protons in an atom's nucleus, defining the element.

Mass number (A)

The sum of protons and neutrons in an atom's nucleus.

Isotopes

Atoms of the same element with different numbers of neutrons.

Cations

Positively charged ions formed when atoms lose electrons.

Anions

Negatively charged ions formed when atoms gain electrons.

Ionic compound

Composed of cations and anions forming neutral species.

Molecular mass

The sum of atomic masses of all atoms in the molecular formula.

Electrolytes

Substances that form ions in water and allow electrical conductivity.

Nonelectrolytes

Substances that dissolve in water as neutral molecules and do not conduct electricity.