Atoms, Elements, and Molecules

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Matter Noun

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[mat-er]

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Matter

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Anything that possesses mass and occupies space, existing in various states such as solid, liquid, gas, or plasma.

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Example: This diagram shows how the particles that make up matter are arranged in its three common states: tightly packed in a solid, close but free to move in a liquid, and far apart in a gas.

Front

Atom Noun

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[at-uhm]

Back

Atom

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The smallest unit of matter that retains all the chemical properties of an element and serves as a basic building block.

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Example: This diagram shows an atom's structure: a central nucleus with protons and neutrons, and electrons orbiting the nucleus in distinct energy shells.

Front

Proton Noun

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[proh-ton]

Back

Proton

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A stable subatomic particle with a positive electric charge, found within the nucleus of every atom.

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Example: This diagram shows a proton (orange sphere) as a particle located inside the central nucleus of an atom, grouped with neutrons.

Front

Neutron Noun

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[noo-tron]

Back

Neutron

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A subatomic particle with no electric charge, found within the nucleus of an atom alongside protons.

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Example: This diagram shows a neutron (blue sphere) is a particle located inside the atom's central nucleus, along with protons (green spheres).

Front

Electron Noun

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[ih-lek-tron]

Back

Electron

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A stable subatomic particle with a negative electric charge, found in the space orbiting an atom's nucleus.

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Example: This diagram shows an electron as a particle that orbits the central nucleus of an atom, which also contains protons and neutrons.

Front

Nucleus Noun

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[noo-klee-uhs]

Back

Nucleus

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The dense, positively charged central region of an atom, composed of protons and neutrons, containing nearly all its mass.

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Example: The nucleus is the dense, central core of an atom, containing positively charged protons and neutral neutrons, with electrons orbiting around it.

Front

Element Noun

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[el-uh-muhnt]

Back

Element

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A pure substance consisting of only one type of atom that cannot be broken down into simpler substances by chemical means.

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Example: This diagram shows a single atom of the element Sodium, with its nucleus (Na) and electrons arranged in shells, illustrating what an element looks like.

Front

Atomic Number Noun

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[uh-tom-ik nuhm-ber]

Back

Atomic Number

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The number of protons in the nucleus of an atom, which uniquely identifies a chemical element on the periodic table.

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Example: This diagram shows an atom's nucleus contains protons (green '+'). The total count of these protons (six in this case) is the atom's atomic number.

Front

Mass Number Noun

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[mas nuhm-ber]

Back

Mass Number

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The total count of protons and neutrons, collectively known as nucleons, within an atom's nucleus.

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Example: This diagram shows the standard notation for an element, indicating that the Mass Number (A) is the superscript number to the left of the element's symbol (X).

Front

Molecule Noun

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[mol-i-kyool]

Back

Molecule

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A group of two or more atoms held together by chemical bonds, representing the smallest unit of a chemical compound.

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Example: This diagram shows a water molecule, which is made of two hydrogen (H) atoms and one oxygen (O) atom chemically bonded together.