The valency of an element can often be determined by examining its position on the periodic table. Elements in the same group often have similar valencies. For example, elements in Group 1 typically have a valency of one, while those in Group 17 have a valency of seven. Additionally, knowledge of common ions and their charges can also help determine valency.
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The valency of an element is determined by its ability to gain, lose, or share electrons to achieve a stable electron configuration. For main-group elements, the valency often corresponds to the number of electrons an element gains or loses to achieve a noble gas configuration. Transition metals may have variable valencies based on their electron configurations and bonding patterns in compounds.