Periodic Table and Chemical Properties

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Periodic Table

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A tabular arrangement of the chemical elements, ordered by their atomic number, electron configuration, and recurring chemical properties. The table shows trends in properties across periods and down groups.

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Period

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A horizontal row in the periodic table. Elements in the same period have the same number of electron shells.

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Group (or Family)

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A vertical column in the periodic table. Elements in the same group have similar chemical properties due to having the same number of valence electrons.

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Atomic Radii

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The average distance between the nucleus and the outermost electron shell of an atom. Trend: Atomic radii generally decrease across a period (left to right) and increase down a group (top to bottom).

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Ion Radii

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The radius of an ion (an atom that has gained or lost electrons). Trend: Cations (positive ions) are smaller than their neutral atoms, and anions (negative ions) are larger than their neutral atoms. Ion radii trends follow similar patterns to atomic radii.

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Ionization Energy

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The minimum energy required to remove an electron from a gaseous atom or ion. Trend: Ionization energy generally increases across a period and decreases down a group.

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Electronegativity

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The measure of an atom's tendency to attract a bonding pair of electrons. Trend: Electronegativity generally increases across a period and decreases down a group.

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Electron Affinity

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The change in energy when an electron is added to a neutral atom to form a negative ion. Trend: Electron affinity trends are complex, but generally become more negative (more energy released) across a period (excluding noble gases) and less negative down a group.

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Valence Electrons

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The electrons in the outermost shell of an atom, which are involved in chemical bonding.

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Alkali Metals (Group 1)

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Highly reactive metals that readily lose one electron to form a +1 ion.