Sergey Bylikin, Gary Horner and, Brian Murphy Solutions for Chapter: Periodicity, Exercise 3: TOK

Mendeleev examined the properties of elements in minute detail and grouped elements with similar properties together. When Mendeleev published his first periodic table of elements in $1869$ he left gaps in the table for as yet undiscovered elements, and hence elements fell into their correct groups. Mendeelev was therefore able to predict the properties of yet undiscovered elements at the time. The predictive power of Mendeleev's periodic table illustrates the "risk taking" nature of science. What is the distinction between scientific and pseudoscientific claims?

The periodic table is an excellent example of classification in science. It classifies elements in several ways-metals, non-metals, and metalloids; main-group and transition elements; groups and periods; elements with acidic, basic, and amphoteric oxides; and $\mathrm{s}, \mathrm{p}, \mathrm{d}$ and $\mathrm{f}$ sublevels. How do classification and categorisation help and hinder the pursuit of knowledge? Why is it incorrect to classify scandium as a non-transition element?