The Nucleus

Front

Nucleus Noun

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[noo-klee-uhs]

Back

Nucleus

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

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Example: This diagram shows a cutaway view of the cell's nucleus, labeling key parts like the nucleolus, chromatin, and the protective nuclear envelope with pores.

Front

Proton Noun

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[proh-ton]

Back

Proton

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

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

Front

Neutron Noun

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[noo-tron]

Back

Neutron

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A subatomic particle with no net electric charge, found within the atomic nucleus, possessing a mass similar to a proton.

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Example: This diagram shows a neutron (blue) located in the central nucleus of an atom, alongside a proton (red), defining its place and neutral nature.

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 that orbits the nucleus of an atom in an electron cloud.

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Example: This diagram of an atom shows electrons as negatively charged particles that orbit the central nucleus in distinct energy shells.

Front

Nucleons Noun

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[noo-klee-ons]

Back

Nucleons

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The collective term for the subatomic particles that make up the atomic nucleus, which are protons and neutrons.

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Example: This diagram shows that the nucleus of an atom is made of two types of particles, protons and neutrons, which are collectively called nucleons.

Front

Atomic Number (Z) Noun

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[uh-tom-ik num-ber]

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Atomic Number (Z)

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The number of protons in an atom's nucleus, which uniquely identifies a chemical element and its chemical properties.

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Example: This diagram of a periodic table element tile shows that the Atomic Number, located at the top, indicates the number of protons in an atom's nucleus.

Front

Mass Number (A) Noun

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[mass num-ber]

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Mass Number (A)

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The total count of protons and neutrons, collectively known as nucleons, found within a single atomic nucleus.

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Example: This diagram shows the standard notation for an element, where the top number is the Mass Number (the total count of protons and neutrons in the nucleus).

Front

Atomic Mass Unit (u) Noun

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[uh-tom-ik mass yoo-nit]

Back

Atomic Mass Unit (u)

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A standard unit of mass for atoms and molecules, defined as one-twelfth the mass of a single carbon-12 atom.

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Example: This diagram of a periodic table tile for Carbon shows that the number at the bottom (12.01) is the atomic mass, measured in atomic mass units.

Front

Isotopes Noun

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[ahy-suh-tohps]

Back

Isotopes

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Variants of a chemical element that have the same number of protons but differ in their number of neutrons.

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Example: This image shows three forms of the Carbon atom, called isotopes. They all have the same number of protons but different numbers of neutrons in their nucleus.

Front

Strong Nuclear Force Noun

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[strong noo-klee-er fors]

Back

Strong Nuclear Force

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A fundamental attractive force that binds nucleons together, holding the atomic nucleus intact against the repulsion between protons.

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Example: This diagram shows the strong nuclear force (arrows) acting between protons and neutrons, holding them tightly together to form the atom's nucleus.