The atomic number of an element refers to the number of protons it has.

The names of elements are also represented by unique one- or two-letter symbols. Each element has a unique number of protons. An element's atomic number is equal to the number of protons in the nuclei of any of its atoms. The mass number of an atom is the sum of the protons and neutrons in the atom.

see the picture for the vector

the magnitude of the vector by pythagorean theorem

r = √( (-10)^2 + (3)^2 ) = √109

magnitude = √109 units

the direction angle between vector and x-axis is

tan^(-1)(3/10) = 16.699

so the direction is approximately 16.7 degrees north of west