The periodic table of elements

In short: The periodic table arranges all chemical elements by increasing atomic number (number of protons) in periods (rows) and groups (columns). Elements in a group have similar properties.

In more detail: Dmitri Mendeleev drew up a first arrangement in 1869. Today 118 elements are known.

In detail

• Main groups: Alkali metals (group 1, reactive), alkaline earth metals (2), halogens (17, form salts), noble gases (18, hardly reactive).
• Metals and non-metals: Mostly metals on the left and in the middle, non-metals on the right. Metalloids such as silicon in between.
• Electron shells: The period gives the number of occupied shells, the main group the number of outer electrons.
• Symbols: H hydrogen, C carbon, O oxygen, Fe iron, Au gold.
• Use: You can predict properties and reactions (ph-wert-saeuren-und-laugen).