Molecules

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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 the characteristic properties of a chemical element.

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Example: This diagram shows an atom's structure, with a central nucleus containing positive protons and neutral neutrons, and negative electrons orbiting the nucleus.

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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 nucleus of an 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.

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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 of an atom alongside protons.

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Example: This diagram shows that neutrons are neutrally charged particles found alongside protons in the central nucleus of an atom, while electrons orbit the nucleus.

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Electron Noun

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[ih-lek-tron]

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Electron

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A negatively charged subatomic particle that occupies shells or orbitals orbiting the atom's nucleus.

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Example: This diagram shows an electron moving between energy shells by absorbing or releasing energy, a key behavior in how atoms form molecules.

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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 an atom's nucleus, which uniquely identifies a specific chemical element.

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Example: This diagram of an oxygen atom shows 8 protons in the nucleus. The number of protons in an atom's nucleus is its atomic number.

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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.

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Example: This diagram shows a Helium atom has 2 protons and 2 neutrons in its nucleus, so its Mass Number (the top number) is 4.

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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 defined as exactly one-twelfth the mass of a single carbon-12 atom.

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Example: The atomic mass unit (amu) is based on the Carbon-12 atom, shown here with 6 protons (P) and 6 neutrons (N) in its nucleus.

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Molecule Noun

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[mol-i-kyool]

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Molecule

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The smallest particle of a substance, composed of two or more atoms chemically bonded together.

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Example: This image shows how a single water molecule (H₂O) is formed by two hydrogen (H) atoms and one oxygen (O) atom bonded together.

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Atomicity Noun

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[at-uh-mis-i-tee]

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Atomicity

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The total number of atoms present in a single molecule of an element or a compound.

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Example: Atomicity is the total number of atoms in a single molecule. This glucose molecule (C₆H₁₂O₆) has an atomicity of 24 (6 carbon + 12 hydrogen + 6 oxygen).

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Ion Noun

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[ahy-on]

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Ion

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An atom or group of atoms that has an electrical charge due to losing or gaining electrons.

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Example: A neutral sodium atom becomes a positive ion (Na+) when it loses an electron, because it then has more positive protons than negative electrons.