Chapter 1: Matter and Energy — Section 1: Matter and Its Classification

Vocabulary flashcards covering pure substances, mixtures, elements, compounds, atoms, molecules, and basic periodic table concepts from Chapter 1 notes.

Pure substance

A substance with the same chemical composition throughout and from sample to sample; it cannot be separated into different substances by physical means.

Mixture

A combination of two or more substances that may have a nonuniform composition and can be separated into the components.

Element

A substance that cannot be broken down into simpler substances by chemical reaction; elements are the basic building blocks of matter and are listed on the periodic table.

Compound

A substance made from two or more elements in a fixed, definite proportion; its properties differ from its constituent elements.

Atom

The smallest unit of an element that retains the element’s chemical properties.

Molecule

Two or more atoms bound together in a discrete arrangement; can be the same element or different elements.

Element symbol

A one- or two-letter abbreviation for an element; first letter is capitalized and a second letter (if present) is lowercase.

Periodic table

A chart that organizes all known elements by properties and increasing atomic number.

Metals

Elements that are typically shiny (have luster) and conduct electricity.

Nonmetals

Elements that are usually dull and poor conductors; they are not shiny.

Metalloids

Elements with properties between metals and nonmetals, located along the staircase line on the periodic table.

Luster

Shininess used to distinguish metals from nonmetals.

Stair-step line

A diagonal line on the periodic table; left of it are metals, right are nonmetals, with metalloids along the line.

Hydrogen molecule (H2)

Two hydrogen atoms bonded together to form a diatomic molecule.

Water (H2O)

A compound made of two hydrogen atoms and one oxygen atom in a 2:1 ratio.

Silicon dioxide (SiO2)

A compound with one silicon atom bonded to two oxygen atoms (SiO2).

Sodium chloride (NaCl)

A compound formed from sodium and chloride ions; common table salt.

Iron pyrite (Fe2S3)

Fool’s gold; a compound of iron and sulfur in a fixed 2:3 ratio.