Final answer:
Calculating the total number of valence electrons in a molecule or ion involves adding the valence electrons of each atom and adjusting for charges if it's a polyatomic ion. Bonds consume two valence electrons, and balancing redox reactions may require multiplying by a coefficient to equalize electrons.
Step-by-step explanation:
To determine the number of valence electrons to use in forming bonds or assigning charges in an ion or molecule, we need to perform a series of steps as outlined in LibreTexts. First, we calculate the total number of valence electrons by adding together the valence electrons from each atom. Elements are positioned in the periodic table in such a way that allows the number of valence electrons to be inferred. For instance, for CO3²⁻, we start by adding the valence electrons from one carbon atom and three oxygen atoms. Since it is a polyatomic ion with a -2 charge, we then add two more electrons to the total count.
Once you've established the initial number of valence electrons, you'll need to account for the electrons consumed by bonding. In a single bond, two valence electrons are used. Therefore, to equalize the electrons during a reaction or to determine the remaining electrons after bonding, you might need to multiply by a specific coefficient. This sometimes involves using Avogadro's number to convert to moles of electrons, and in balancing redox reactions, adjusting half-reactions so the number of electrons gained and lost are equal.