The pH scale is mathematically defined as:

1. pH is a logarithmic scale specifically built around hydrogen ion concentration, not a direct or square-root measure of it. 2. The text explains: "calculated as the negative of the base 10 logarithm of this concentration. The log10 of 1 x 10-7 is -7.0, and the negative of" that value gives pH 7. 3. This is why a neutral solution with [H+] = 1x10⁻⁷ M has pH = 7, not the raw exponent -7 itself. 4. So pH is defined as the negative base-10 logarithm of hydrogen ion concentration, not the raw concentration, a hydroxide-based logarithm, or a square root. _Source: OpenStax Biology Ch 2 "The Chemical Foundation of Life", p.51 §2.2 | Water_