valence

A whole number (positive or negative) representing the power of one element to combine with another. In general terms, the valence number represents the number of electrons in an atom or combined group of atoms which can be easily given up or accepted to react with or bond to another atom or group of atoms to form a molecule. Example: Two hydrogen ions (each with a valence of +1) must be present for each ion of oxygen (-2) to form a molecule of water (H₂O).

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