However when considering ions, you do have to think distinctly about cations and anions. Calcium forms a positively charged +2 cation. Chlorine forms a negatively charged -1 anion.

R.J. HAYNES, Active ion uptake and maintenance of cation-anion balance: A critical examination of their role in regulating rhizosphere pH, Plant and Soil, Vol. 126, No. 2 (August (II), 1990), pp.