Structure of an Atom – Key Vocabulary

Vocabulary flashcards covering fundamental terms from the lecture on atomic structure, subatomic particles, atomic numbers, mass, isotopes, and related concepts.

Matter

Anything that has mass and takes up space; composed of atoms.

Atom

The basic building block of matter; each element is made of one type of atom that cannot be broken into a simpler substance.

Subatomic Particle

Particles that make up an atom: protons, neutrons, and electrons.

Nucleus

Small, dense, positively-charged center of the atom containing most of its mass.

Proton

Positively charged (+1) subatomic particle located in the nucleus; its count equals the atomic number.

Neutron

Electrically neutral subatomic particle found in the nucleus; contributes to atomic mass.

Electron

Negatively charged (-1) subatomic particle that orbits the nucleus in specific energy levels.

Electron Cloud

Region around the nucleus where electrons are likely to be found in various energy levels.

Energy Level

Fixed region of the electron cloud where electrons with similar energy are located.

Valence Electron

Electron located in the outermost energy level of an atom; determines chemical reactivity.

Atomic Number (Z)

Number of protons in an atom’s nucleus; uniquely identifies an element.

Atomic Mass (Average Atomic Mass)

Weighted average mass of an element’s naturally occurring isotopes, expressed in atomic mass units (amu).

Atomic Mass Unit (amu)

SI unit for atomic mass; 1 amu ≈ mass of one proton or one neutron.

Mass Number (A)

Whole-number sum of protons and neutrons in a single atom.

Isotope

Atoms of the same element (same Z) that have different numbers of neutrons (different A).

Isotopic Symbol

Notation showing an isotope as A/Z X, where X is the element symbol, A the mass number, and Z the atomic number.

Ion

Atom with a net electric charge due to loss or gain of electrons.

Neutral Atom

Atom in which the number of electrons equals the number of protons, resulting in no net charge.

Charge of an Atom

Overall electrical state determined by the difference between protons and electrons; electrons are easily gained or lost to create ions.

Relationship of Protons and Electrons

In a neutral atom, the number of electrons equals the number of protons.

Calculating Neutrons

Number of neutrons = Mass number – Atomic number (n = A – Z).

2-8-8 Rule

Electron-filling pattern where the first three energy levels hold a maximum of 2, 8, and 8 electrons (for the first 18 elements).

Building Blocks of Matter

Nickname for atoms because all matter is composed of them.

Unique Atomic Number

Fact that every element has its own distinct number of protons, giving each a unique atomic number.

Periodic Table Information

Element boxes show the atomic number (top), symbol, name, and average atomic mass (bottom).