Final answer:
To find the number of valence electrons in an electron configuration, count the electrons in the highest-numbered shell and any in the last unfilled subshell. For molecules or ions, add the valence electrons from each atom and adjust for any charges by adding or subtracting electrons accordingly.
Step-by-step explanation:
To find the number of valence electrons from an electron configuration, you should consider the electrons present in the highest-numbered shell, as well as any electrons in the last unfilled subshell. The correct strategy is to look at the electron configuration and identify the electrons in the valence shell. For example, the electron configurations for the alkali metals (H, Li, Na, K, Rb, Cs) all end with s1, indicating they all have one valence electron.
To determine the total number of valence electrons in a molecule or polyatomic ion, you need to add together the valence electrons from each atom. In addition, if the species has a negative charge, such as CO32-, you add two electrons to the total count because of its -2 charge.
Lastly, it's important to note that for cations (positive ions), you must subtract an electron for each positive charge, and for anions (negative ions), you need to add an electron for each negative charge to arrive at the total number of valence electrons.
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