Unstable Nuclei and Radioactive Decay

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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, composed of protons and neutrons, where nuclear reactions occur.

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Example: This diagram shows the nucleus at the center of an atom and a magnified view revealing it is made of protons and neutrons.

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Nuclear Reaction Noun

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[noo-klee-er ree-ak-shun]

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Nuclear Reaction

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A process that involves a change in an atom's nucleus, often resulting in the formation of a new element.

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Example: A neutron hits a large, unstable nucleus, causing it to split. This releases more neutrons, which then hit other nuclei, creating a chain reaction.

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Radioactive Decay Noun

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[ray-dee-oh-ak-tiv di-kay]

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Radioactive Decay

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The spontaneous process by which an unstable atomic nucleus loses energy by emitting radiation to become more stable.

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Example: This graph shows that during radioactive decay, the amount of a substance decreases by half over a set period called a 'half-life'.

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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 (1+) located in the nucleus, defining an element's atomic number.

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Example: This diagram shows a proton (red sphere) as a key particle located inside an atom's central nucleus, along with uncharged neutrons.

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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 located in the nucleus; variations in its number create different isotopes.

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Example: This diagram shows a neutron (n), a particle with no charge, located inside the atom's nucleus along with positively charged protons (p+).

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Atomic Number Noun

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[uh-tom-ik num-ber]

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Atomic Number

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The number of protons in an atom's nucleus, which uniquely identifies a chemical element and is denoted by Z.

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Example: This diagram of an oxygen atom shows 8 protons in its nucleus, which defines its atomic number as 8.

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Mass Number Noun

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[mas num-ber]

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Mass Number

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The total number of protons and neutrons found within the nucleus of an atom, denoted by the symbol A.

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Example: This diagram shows that the Mass Number (A) is the total count of protons and neutrons in an atom's nucleus, using a Helium atom as an example.

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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 versions of a hydrogen atom; each has one proton but a different number of neutrons, making them isotopes of each other.

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Radioactivity Noun

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[ray-dee-oh-ak-tiv-i-tee]

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Radioactivity

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The spontaneous emission of radiation from the nucleus of an unstable atom as it undergoes decay to become stable.

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Example: An unstable nucleus (like uranium-238) becomes more stable by releasing a small particle (an alpha particle), changing into a new, lighter nucleus (like thorium-234).

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Nuclear Equation Noun

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[noo-klee-er ih-kwey-zhuhn]

Back

Nuclear Equation

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A symbolic representation of a nuclear reaction, showing reactants and products with their respective atomic and mass numbers.

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Example: An unstable Uranium-238 nucleus (parent) decays into a more stable Thorium-234 nucleus (daughter) by emitting an alpha particle, balancing the nuclear equation.