Atomic Theory

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Atom Noun

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[at-uhm]

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Atom

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The smallest particle of a chemical element, consisting of a nucleus with protons and neutrons, surrounded by electrons.

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Example: An atom consists of a central nucleus, containing protons and neutrons, which is orbited by electrons moving in distinct paths called electron shells.

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Electron Noun

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[ih-lek-tron]

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Electron

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A stable, negatively charged subatomic particle that orbits the nucleus of an atom in a region called a cloud.

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Example: This diagram shows negatively charged electrons orbiting the central nucleus of an atom, which also contains protons and neutrons.

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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, that contains most of its mass.

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Example: This diagram shows the nucleus, the central part of an atom, which contains the protons (positive charge) and neutrons (no charge).

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Proton Noun

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[proh-ton]

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Proton

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A stable, positively charged subatomic particle with significant mass that is found within the nucleus of an atom.

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Example: This diagram shows a proton, a particle with a positive charge (+), located in the center (nucleus) of a simple atom.

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Neutron Noun

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[noo-tron]

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Neutron

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An electrically neutral subatomic particle with a mass similar to a proton, located within the nucleus of an atom.

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

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Atomos Noun

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[at-uh-mohs]

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Atomos

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The ancient Greek term, meaning 'uncuttable,' used by Democritus to describe the indivisible particles he believed composed all matter.

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Example: This image shows the philosopher Democritus, who first proposed the 'Atomos' model, suggesting matter is made of tiny, indivisible particles of different shapes.

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Molecule Noun

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[mol-i-kyool]

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Molecule

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An electrically neutral group of two or more atoms held together by chemical bonds, forming the smallest unit of a compound.

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Example: This image shows a water molecule, which is made of one oxygen atom and two hydrogen atoms chemically bonded together.

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Alpha Particle Noun

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[al-fuh pahr-ti-kuhl]

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Alpha Particle

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A positively charged particle consisting of two protons and two neutrons, used in experiments like Rutherford's gold foil test.

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Example: This diagram shows a large atomic nucleus (Uranium-235) releasing an alpha particle, which is identical to a helium nucleus, during radioactive decay.

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Gamma Rays Noun

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[gam-uh reyz]

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Gamma Rays

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Penetrating electromagnetic radiation arising from the radioactive decay of atomic nuclei, sometimes used in particle experiments.

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Example: This diagram shows the electromagnetic spectrum, where gamma rays have the shortest wavelength and highest energy compared to other waves like X-rays and radio waves.

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Beta Particle Noun

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[bey-tuh pahr-ti-kuhl]

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Beta Particle

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A high-speed, high-energy electron or positron emitted in the radioactive decay of an atomic nucleus during beta decay.

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Example: This diagram shows that a beta particle is a high-energy electron that is released when a neutron inside an atom's nucleus changes into a proton.