Category
Element categories refer to groups of elements whose electrical conductivities are similar. They serve as a basic classification of the classical periodic table.
Nonmetals
Nonmetals are characterized by missing properties such as electrical and thermal conductivity, hardness, their gloss and good formability. They have the generally highest electron affinity.
Noble gases
Noble gases (inert gases or inert gases) form the 8th main group. They have only completely filled atomic orbitals, enter reactions only under extreme conditions and do not form molecules with each other.
Alkali metals
Alkali metals are all elements of the 1st main group. The reactive metals have a silvery shiny appearance, low densities and have only one weakly bound s-electron.
Alkaline earth metals
Alkaline earth metals include all elements of the 2nd main group. The light metals are poorly soluble in water, shine metallically, oxidize and are stable in dry air.
Metalloids
Metalloids stand between metals and non-metals, which they are not assignable due to their electrical conductivity and their appearance. They have semiconducting and amphoteric properties.
Halogens
Halogens refer to elements of the 7th main group, are very reactive in their elemental state, colored and react with metals to form salts. Their name (corpora halogenia) goes back to Jöns Jakob Berzelius.
Metals
Metals are electrically conductive elements to the left and below a dividing line from boron to astatine. They also have high thermal conductivity, ductility (deformability) and metallic gloss (mirror gloss).
Transition metals
Transition metals are called metals of the subgroup elements. They have high tensile strengths, densities, melting points and boiling points. Characteristic is an increase of electrons in the d-atomic orbitals along each period.
Lanthanides
Lanthanides is a group designation for similar, silvery-shining, relatively soft and reactive metals. Almost all have a typical dense sphere packing. Their hardness increases with increasing atomic number.
Actinides
Actinides are similar elements of the 7th period. The heavy metals have nuclear properties and are neutron-induced fissionable. Some actinides are pyrophoric in finely divided state.
Unknown
Elements of this category are not assigned to any of the known element categories.