Atomic Mass

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Atom Noun

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[at-uhm]

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Atom

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The smallest unit of matter that retains all the chemical properties of an element and is composed of subatomic particles.

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Example: This diagram shows an oxygen atom's nucleus contains 8 protons and 8 neutrons, which are added together to determine the atom's mass.

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Proton Noun

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[proh-ton]

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Proton

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A subatomic particle with a positive electric charge, found within the atomic nucleus and having a mass of one AMU.

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Example: This diagram shows protons (green spheres) clustered with neutrons in the atom's central nucleus, which contains nearly all the atom's mass.

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Neutron Noun

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[noo-tron]

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Neutron

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

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Example: This diagram shows a neutron as a neutral particle located in the atom's nucleus, where it contributes to the atom's total atomic mass.

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Electron Noun

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[ih-lek-tron]

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Electron

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A subatomic particle with a negative electric charge that orbits the nucleus of an atom in specific energy levels or shells.

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Example: This diagram shows an electron orbiting the nucleus, which contains protons and neutrons. Electrons have negligible mass compared to protons and neutrons, which make up the atomic mass.

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Nucleus Noun

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[noo-klee-uhs]

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Nucleus

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

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Example: This diagram shows the nucleus is the dense center of an atom, containing particles (protons and neutrons) that make up most of its atomic mass.

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Quark Noun

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[kwark]

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Quark

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A fundamental constituent of matter that combines in groups to form composite particles like protons and neutrons.

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Example: This diagram shows that a proton, a key part of an atom's nucleus, is made of even smaller fundamental particles called quarks (two 'up' and one 'down').

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Atomic Number Noun

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[uh-tom-ik nuhm-ber]

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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 of an Oxygen atom uses a key to show that its Atomic Number is 8 and its Atomic Weight (Mass) is 15.999.

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Mass Number Noun

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[mas nuhm-ber]

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Mass Number

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

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Example: This diagram shows that the mass number (27) is the sum of the protons (13) and neutrons (14) in an atom's nucleus.

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Isotope Noun

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[ahy-suh-tohp]

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Isotope

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Variants of a particular chemical element which differ in neutron number but have the same number of protons and electrons.

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Example: Isotopes are versions of an element with the same number of protons but a different number of neutrons, resulting in a different atomic mass.

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Atomic Mass Unit (AMU) Noun

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[uh-tom-ik mas yoo-nit]

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Atomic Mass Unit (AMU)

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

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Example: An atom's mass, measured in Atomic Mass Units (AMU), is determined by counting the protons (P) and neutrons (N) in its central nucleus.