Final answer:
To determine the valence electrons for a negative ion like CHO₂⁻, add the valence electrons from each atom and an extra electron for the negative charge. Then, subtract the electrons used in bonding to find the remaining valence electrons.
Step-by-step explanation:
To determine the number of valence electrons in a molecule or ion, such as CHO₂⁻, you need to first add the valence electrons from each atom based on its position in the periodic table.
Then, since CHO₂⁻ is a negative ion, you would add an extra electron for each negative charge it possesses. In this case, the ion has a single negative charge, so we add one electron.
Once the total number of valence electrons is found, we need to account for electrons used in bonding. According to LibreTexts™, every single bond consumes two valence electrons. Therefore, to find the remaining valence electrons after bond formation, subtract the number of electrons consumed in bonds from the total valence electrons initially present.