Atomic Mass and Mass Number

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Atom Noun

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[at-uhm]

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Atom

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The basic unit of a chemical element, consisting of a central nucleus surrounded by one or more electrons.

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Example: This diagram shows an atom's nucleus, containing protons and neutrons, which together determine the atom's mass number, and the orbiting electrons.

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Subatomic Particle Noun

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[suhb-uh-tom-ik par-ti-kuhl]

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Subatomic Particle

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A particle smaller than an atom, such as a proton, neutron, or electron, which are the constituents of atoms.

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Example: This diagram shows an atom's three types of subatomic particles: protons and neutrons in the central nucleus, and electrons orbiting the nucleus in shells.

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Proton Noun

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[proh-ton]

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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 (red sphere) located inside the atom's central nucleus, which is essential for understanding its contribution to atomic 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 electric charge and a mass similar to a proton, located in the atom's nucleus.

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Example: This diagram shows a neutron is a particle found inside the atom's central core, the nucleus, along with protons.

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Electron Noun

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[ih-lek-tron]

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Electron

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

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Example: This Bohr model shows electrons as particles orbiting the central nucleus of an oxygen atom, illustrating their location within the atom's structure.

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Nucleus Noun

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[noo-klee-uhs]

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Nucleus

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The dense, positively charged central region of an atom, which is composed of both protons and neutrons.

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Example: This diagram shows the nucleus at the center of an atom, containing protons and neutrons, which together determine the atom's mass number.

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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.

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Example: The image shows that the atomic number of an element, like Fluorine's 9, is found on the periodic table and equals the number of protons in the atom's nucleus.

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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 number of protons and neutrons combined within a single atomic nucleus for a specific isotope.

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Example: This image shows that the mass number (27) is the total count of 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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Atoms of the same element that have the same number of protons but a different number of neutrons.

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Example: This image shows three isotopes of hydrogen; each has one proton, but a different number of neutrons, resulting in different mass numbers.

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Atomic Mass Noun

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[uh-tom-ik mas]

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Atomic Mass

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The weighted average mass of all the naturally occurring isotopes of a particular chemical element, expressed in amu.

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Example: This diagram of an element's square from the periodic table shows that the atomic mass (15.999) is the decimal number, distinct from the atomic number.