How would I find the number of protons, neutrons and electrons when I only have the atomic number and atom (assignment says assume the net charge is 0)

Explanation:

Atomic number , protons and electrons have the same value / their value is same .

But for the neutron there is no specific technique. You have to remember the neutrons of every element

since electrons are negative the answer is neagtaive

atomic mass = 39

number of neutrons = 20

number of protons= 19

electronic configuration = 1s2 2s2 2p6 3s2 3p6 4s1

the number of electron in first shell = 2

number of electrons in n=3 shell = 8