To determine the total number of valence electrons in a molecule like H2CO (formaldehyde), we need to consider the valence electrons contributed by each atom.
H (hydrogen) has 1 valence electron. C (carbon) has 4 valence electrons. O (oxygen) has 6 valence electrons.
In H2CO, there are two hydrogen atoms, one carbon atom, and one oxygen atom. Adding up the valence electrons from each atom:
2 (hydrogen atoms) × 1 (valence electron per hydrogen) = 2 valence electrons from hydrogen 1 (carbon atom) × 4 (valence electrons per carbon) = 4 valence electrons from carbon 1 (oxygen atom) × 6 (valence electrons per oxygen) = 6 valence electrons from oxygen
Adding these together, we get a total of 2 + 4 + 6 = 12 valence electrons in H2CO.