7th Grade Physical Science Review

Front

Atom Noun

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[at-uhm]

Back

Atom

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The basic unit of a chemical element, consisting of a dense central nucleus surrounded by a cloud of electrons.

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Example: An atom consists of a central nucleus, containing positive protons and neutral neutrons, which is orbited by negative electrons.

Front

Proton Noun

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[proh-ton]

Back

Proton

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A stable subatomic particle with a positive electric charge, found within the atomic nucleus of every element.

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Example: This diagram shows a model of an atom, identifying protons as the green particles clustered with neutrons inside the central nucleus.

Front

Neutron Noun

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[noo-tron]

Back

Neutron

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A subatomic particle without an electric charge, present in all atomic nuclei except for ordinary hydrogen.

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Example: This diagram shows that neutrons are particles found inside the nucleus of an atom, along with protons, while electrons orbit the nucleus.

Front

Electron Noun

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[ih-lek-tron]

Back

Electron

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A stable subatomic particle with a negative electric charge that orbits the nucleus of an atom.

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

Front

Nucleus Noun

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[noo-klee-uhs]

Back

Nucleus

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The 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 at the center of an atom, containing protons and neutrons, with electrons orbiting around it.

Front

Element Noun

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[el-uh-muhnt]

Back

Element

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A pure substance consisting only of atoms that all have the same numbers of protons in their atomic nuclei.

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Example: This diagram shows an atom of the element Oxygen. An element is a pure substance defined by the number of protons in its atoms (8 for Oxygen).

Front

Molecule Noun

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[mol-i-kyool]

Back

Molecule

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An electrically neutral group of two or more atoms held together by attractive forces known as chemical bonds.

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Example: This diagram shows a carbon dioxide (CO₂) molecule, where one carbon atom is chemically bonded to two oxygen atoms, forming a single unit.

Front

Compound Noun

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[kom-pound]

Back

Compound

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A substance formed when two or more different chemical elements are chemically bonded together in a fixed ratio.

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Example: This diagram shows a water molecule (H₂O), a classic example of a compound, where two different elements, hydrogen (H) and oxygen (O), are chemically bonded together.

Front

Isotope Noun

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[ahy-suh-tohp]

Back

Isotope

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

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Example: This diagram shows three forms of hydrogen. All have one proton, making them hydrogen, but they are isotopes because they have different numbers of neutrons.

Front

Ion Noun

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[ahy-on]

Back

Ion

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An atom or molecule with a net electric charge due to the loss or gain of one or more electrons.

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Example: A neutral sodium atom (Na) loses an electron to become a positively charged sodium ion (Na+), because it now has more protons than electrons.