Any pure water sample contains 2 g of hydrogen for every 16 g of oxygen. An isotope of hydrogen that contains one neutron and one proton in its nucleus. A property used to explain attractions and repulsions between certain objects. An element is a substance composed of atoms with identical atomic number . An international abbreviation for element names, usually consisting of the first one or two distinctive letters in element name.
Some symbols are abbreviations for ancient names.
A substructure that imparts characteristic chemical behaviors to a molecule, for example, a carboxylic acid group. A vertical column on the periodic table, for example, the halogens . Elements that belong to the same group usually show chemical similarities, although the element at the top of the group is usually atypical. An atom or molecule that has acquired a charge by either gaining or losing electrons. Compare with isomer , allotrope , isobar , and isotone .