The zigzag, staircase, line in the diagram of the periodic table above separates the metals, on the left, from non-metals, on the right. Hydrogen is a non-metal, but it is often put in the middle.

Want to learn more about this centerpiece of chemistry? Take your pick from this collection of links about elements and the periodic table! Build an element ball, solve periodic puzzles, and check out ...

Electronegativity, an essential characteristic of all elements in the periodic table, measures an atom's ability to attract ... with a large difference indicating a polar covalent bond (e.g., H-F bond ...

Browse a list of curated classroom activities by the American Association of Chemistry Teachers. Lesson Plans: The Periodic Table and Bonding Download inquiry-based lesson plans and activity sheets to ...

On 17 February 1869, Russian chemist Dmitri Mendeleev jotted down the symbols for the chemical elements, putting them in order according to their atomic weights and inventing the periodic table.