Final answer:
To determine the total number of valence electrons in a molecule or ion, add up the valence electrons from each atom. Adjust for the charge if it's a polyatomic ion. Examples include CO2 with 16 valence electrons, and CH4 with 8.
Step-by-step explanation:
Determining the Total Number of Valence Electrons
To determine the total number of valence electrons in a molecule or ion, begin by adding together the valence electrons from each atom based on their position in the periodic table. For instance, each hydrogen atom has one valence electron, each carbon atom has four, and each oxygen atom has six. When dealing with a polyatomic ion, like CO32-, adjust the total by adding or subtracting electrons according to the ion's charge. As an example:
- For CH4, the total valence electrons are 4 (C) + 4x1 (H) = 8 valence electrons.
- For PCl3, the calculation is 5 (P) + 7x3 (Cl) = 26 valence electrons.
- For CO2, it's 4 (C) + 6x2 (O) = 16 valence electrons.
- For HCN, the sum is 1 (H) + 4 (C) + 5 (N) = 10 valence electrons.
Keep in mind, the bonding pair of electrons counts towards the total valence electrons of each bonded atom.