Answer:
The atomic number gives the number of protons 19
p = 19
The atomic mass is the sum of the protons and neutrons
p+n = 39 p = 19
Put p into the equation and solve for n the neutrons
19+n = 39
Subtract 19 from both sides
19-19+n = 39-19
n = 20
The number of electons equal the number of protons in a neutral atom. The positive charge equal to the negative charge. The negative charge is the number of electons. This ion has a charge of +1. So solve for the negative charge.
-19+1 = -18
The negative charge is -18 so
e = 18