Periodic table centre and the transition metals, lanthanides, and actinides occupying peninsulas. Most periodic tables are two-dimensional; three-dimensional tables are known to as far back as at least 1862 (pre-dating Mendeleev's two-dimensional table of 1869). More recent examples include Courtines' Periodic Classification (1925), Wringley's Lamina System (1949), Giguère's Periodic helix (1965) and Dufour's Periodic Tree (1996). Going one further, Stowe's Physicist's Periodic Table (1989) has been described as being four-dimensional (having three spatial dimensions and one colour dimension). The various forms of periodic tables can be thought of as lying on a chemistry–physics continuum. Towards the chemistry end of the continuum can
Element-reactant-product table reaction equation is not balanced, it needs coefficients to show equality. Here is an example with the separation of natural gas from hydrochloric acid using magnesium.<br> Mg + HCl = MgCl + H <br>Here is the element-reaction-product table:<br> From this table we see that the number of hydrogen and chlorine atoms on the product's side are twice the number of atoms on the reactant's side. Therefore, we add the coefficient "2" in front of the HCl on the products side, to get our equation to look like this:<br> Mg + 2HCl = MgCl + H<br> and our table looks like