Card 2 / 19: Visit this website ( http://openstaxcollege.org/l/ptable ) to view the periodic table. In the periodic table of the elements, elements in a single column have the same number of electrons that can participate in a chemical reaction. These electrons are known as "valence electrons." For example, the elements in the first column all have a single valence electron-an electron that can be "donated" in a chemical reaction with another atom. What is the meaning of a mass number shown in parentheses?

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