Question

How to find the number of electrons taking part in a reaction?

Answer 1

on the basis of atomic number

Answer 2

Analyze the chemical formula and write down the element types that comprise the compound as well as the number of atoms of each type. The first example, KNO3, contains the elements potassium (K—1 atom), nitrogen (N—1 atom) and oxygen (O—3 atoms). The second example, SO42-, contains the elements sulfur (S—1 atom) and oxygen (O—4 atoms).

Navigate to the periodic table of the chemical elements (see Resources) and find out the integer atomic number for each element identified in Step 1—the number that appears just above the chemical symbol for each element. In our example, the atomic numbers of the elements potassium (K), nitrogen (N), oxygen (O) and sulfur (S) are 19, 7, 8 and 16, respectively.
Analyze the chemical formula and write down the element types that comprise the compound as well as the number of atoms of each type. The first example, KNO3, contains the elements potassium (K—1 atom), nitrogen (N—1 atom) and oxygen (O—3 atoms). The second example, SO42-, contains the elements sulfur (S—1 atom) and oxygen (O—4 atoms).

Navigate to the periodic table of the chemical elements (see Resources) and find out the integer atomic number for each element identified in Step 1—the number that appears just above the chemical symbol for each element. In our example, the atomic numbers of the elements potassium (K), nitrogen (N), oxygen (O) and sulfur (S) are 19, 7, 8 and 16, respectively.

Multiply the element’s atomic number by the number of atoms of this type (see Step 1) in the molecule. Repeat for all elements in the molecule, then add up all the products to calculate the number of electrons. In the first example, the number of electrons in KNO3 equals (19 x 1) + (7 x 1) + (8 x 3) = 50. In the second example, the number of electrons in SO42- equals (16 x 1) + (8 x 4) = 48.