Periodic Trends

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Periodic Law Noun

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[peer-ee-od-ik law]

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Periodic Law

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The principle that chemical and physical properties of elements repeat periodically when arranged by increasing atomic number.

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Example: This diagram shows that as you move across or down the periodic table, properties like atomic size change in a predictable, repeating pattern.

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Period Noun

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[peer-ee-ud]

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Period

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A horizontal row in the periodic table, where the period number corresponds to the principal energy level of valence electrons.

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Example: This Bohr model shows that a Sodium (Na) atom has three electron shells, which is why it is located in Period 3 of the periodic table.

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Group Noun

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[groop]

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Group

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A vertical column in the periodic table, also known as a family, containing elements with similar chemical properties.

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Example: This image shows the elements of a periodic table group (Alkali Metals), illustrating that as you move down a group, the number of electron shells increases.

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Valence Electrons Noun

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[vay-lence ee-lek-trons]

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Valence Electrons

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The electrons in an atom's outermost orbitals that are involved in forming chemical bonds and determine chemical properties.

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Example: This diagram of an oxygen atom shows the six electrons in the outermost shell, which are the valence electrons.

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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 an element and organizes the periodic table.

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Example: An atom's atomic number is the number of protons in its nucleus; for Helium, the atomic number is 2 because it has 2 protons.

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Metal Noun

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[met-l]

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Metal

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An element that is typically shiny, solid, malleable, ductile, and a good conductor of heat and electricity.

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Example: This image shows cubes of various elements, most of which are metals, labeled with their name, symbol, atomic number, and atomic mass.

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Nonmetal Noun

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[non-met-l]

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Nonmetal

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An element that is generally a gas or a dull, brittle solid and a poor conductor of heat and electricity.

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Example: This periodic table highlights the nonmetal elements in yellow, showing they are located on the upper right side, separated from metals by a staircase line.

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Metalloid Noun

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[met-uh-loid]

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Metalloid

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An element that exhibits physical and chemical properties that are intermediate between those of metals and nonmetals.

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Example: This image shows the metalloids as a stair-step line on the periodic table, separating the metals from the non-metals.

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Representative Element Noun

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[rep-ri-zen-tuh-tiv el-uh-ment]

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Representative Element

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An element belonging to the s-block or p-block, which includes groups 1, 2, and 13 through 18.

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Example: This periodic table uses color-coding to show that representative elements are the elements in the main groups (the tall columns on the left and right).

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Alkali Metal Noun

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[al-kuh-lie met-l]

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Alkali Metal

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A highly reactive metallic element found in Group 1 of the periodic table, excluding hydrogen.

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Example: This image shows the periodic table and highlights the alkali metals in the first column (Group 1), identifying their specific location.