The Structure of Matter (Water Treatment Foundations)

A vocabulary set covering key terms from the Structure of Matter lecture: matter, elements, atoms, subatomic particles, isotopes, ions, and the periodic table.

Matter

Anything that occupies space and has weight (mass).

Element

The building blocks of the universe; all matter is made of elements.

Atom

Smallest unit of an element that retains the element's properties.

Nucleus

Center of the atom; contains protons and neutrons and holds most of the atom's mass.

Proton

Positively charged particle in the atomic nucleus.

Neutron

Electrically neutral particle in the nucleus; similar in mass to protons.

Electron

Negatively charged particle that orbits the nucleus in electron shells and occupies most of the atom's space.

Subatomic particles

Particles smaller than atoms, including protons, neutrons, and electrons.

Atomic Number

The number of protons in the nucleus of an atom.

Atomic Weight

The sum of the protons and neutrons in the nucleus; for elements with isotopes, it is the weighted average of principal isotopes.

Isotopes

Atoms of the same element with the same number of protons but different numbers of neutrons.

Principal Isotopes

The most common neutron counts for a given element.

Ion

An atom with unequal numbers of protons and electrons, carrying a net electrical charge.

Cation

A positively charged ion (more protons than electrons).

Anion

A negatively charged ion (more electrons than protons).

Electron Shells

Regions surrounding the nucleus where electrons are found; determines an atom's chemistry.

Periodic Table

A table organizing elements by increasing atomic number into periods and groups.

Periods

Horizontal rows; elements in the same period have the same number of electron shells.

Groups

Vertical columns; elements in the same group have similar chemical properties.

Neutral Atom

An atom with equal numbers of protons and electrons (no net charge).