Elements and Compounds

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Element Noun

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[el-uh-muhnt]

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Element

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A pure substance that cannot be separated into simpler substances by any physical or chemical means.

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Example: This diagram shows an atom of Oxygen, a specific element. All elements are made of a single type of atom, defined by their number of protons.

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Pure Substance Noun

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[pyoor suhb-stuhns]

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Pure Substance

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A substance, either an element or a compound, that possesses a uniform and unchanging chemical composition.

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Example: This bar of 'fine gold' is an element, which is a type of pure substance because it is made up of almost 100% gold atoms.

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Chemical Symbol Noun

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[kem-i-kuhl sim-buhl]

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Chemical Symbol

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A unique one, two, or three-letter abbreviation universally used by scientists to represent a specific chemical element.

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Example: This image shows the periodic table entry for Gold. The large letters 'Au' in the center are the chemical symbol, a unique abbreviation for the element.

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Periodic Table Noun

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[peer-ee-od-ik tey-buhl]

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Periodic Table

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A chart organizing elements into rows and columns based on their atomic number and recurring chemical properties.

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Example: This image displays the periodic table, a chart that organizes all known chemical elements by their atomic number, electron configuration, and recurring chemical properties.

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Periods Noun

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[peer-ee-uhds]

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Periods

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The horizontal rows in the periodic table of elements, with each row representing a principal energy level.

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Example: This diagram shows the outline of the periodic table, highlighting that the horizontal rows are called periods.

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Groups Noun

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[groops]

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Groups

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The vertical columns in the periodic table, containing elements that share similar chemical and physical properties.

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Example: This image shows the Noble Gases, which are all in the same group (column) on the periodic table and share similar properties, like having a full outer shell of electrons.

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Compound Noun

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[kom-pound]

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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 molecule of carbon dioxide (CO₂), a compound formed when one carbon atom chemically bonds with two oxygen atoms.

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Chemical Formula Noun

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[kem-i-kuhl fawr-myuh-luh]

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Chemical Formula

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A representation showing the types and numbers of atoms in a single molecule of a substance using symbols and subscripts.

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Example: The image shows a model of a methane molecule and its chemical formula, CH₄, which uses symbols and numbers to represent its composition.

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Subscript Noun

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[suhb-skript]

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Subscript

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A number in a chemical formula written to the lower right of a symbol indicating the number of atoms of that element.

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Example: In a chemical formula like H₂O, the subscript '2' indicates there are two hydrogen atoms in one molecule of water.

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Electrolysis Noun

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[ih-lek-trol-uh-sis]

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Electrolysis

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A process that uses a direct electric current to drive an otherwise non-spontaneous chemical reaction, like separating compounds.

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Example: This diagram shows electrolysis, where an electric current in a liquid separates a compound. Positive ions (cations) move to the negative cathode, and negative ions (anions) move to the positive anode.