Glossary: The periodic table

actinide.

Elements 89-102 are called actinides. Electrons added during the Aufbau construction of actinide atoms go into the 5f subshell. Actinides are unstable and undergo radioactive decay. The most common actinides on Earth are uranium and thorium.

alkali metal. (alkaline earth metal) alkali metal element.

The Group 1 elements, lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr) react with cold water for form strongly alkaline hydroxide solutions, and are referred to as "alkali metals". Hydrogen is not considered an alkali metal, despite its position on some periodic tables.

alkaline earth.

An oxide of an alkaline earth metal, which produces an alkaline solution in reaction with water.

alkaline earth metal. (alkali metal)

The Group 2 elements, beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra) form alkaline oxides and hydroxides and are called "alkaline earth metals".

amphoteric. ampholyte.

A substance that can act as either an acid or a base in a reaction. For example, aluminum hydroxide can neutralize mineral acids ( Al(OH)₃ + 3 HCl = AlCl₃ + 3 H₂O ) or strong bases ( Al(OH)₃ + 3 NaOH = Na₃AlO₃ + 3 H₂O).

atomic radius. metallic radius; covalent radius; atomic radii. Compare with ionic radius.

One half the distance between nuclei of atoms of the same element, when the atoms are bound by a single covalent bond or are in a metallic crystal. The radius of atoms obtained from covalent bond lengths is called the covalent radius; the radius from interatomic distances in metallic crystals is called the metallic radius.

block.

A region of the periodic table that corresponds to the type of subshell (s, p, d, or f) being filled during the Aufbau construction of electron configurations.

congener.

1. Elements belonging to the same group on the periodic table. For example, sodium and potassium are congeners. 2. Compounds produced by identical synthesis reactions and procedures.

first ionization energy. (IE,IP) first ionization potential. Compare with second ionization energy, adiabatic ionization energy, vertical ionization energy, electronegativity, and electron affinity.

The energy needed to remove an electron from an isolated, neutral atom.

group.

1. A substructure that imparts characteristic chemical behaviors to a molecule, for example, a carboxylic acid group. (also: functional group). 2. 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.

halogen. group VIIA; group 18.

An element of group VIIA (a. k. a. Group 18). The name means "salt former"; halogens react with metals to form binary ionic compounds. Fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At) are known at this time.

ionic radius. Compare with atomic radius.

The radii of anions and cations in crystalline ionic compounds, as determined by consistently partitioning the center-to-center distance of ions in those compounds.

ionization energy. (IE,IP) ionization potential. Compare with adiabatic ionization energy, vertical ionization energy, electronegativity, and electron affinity.

The energy needed to remove an electron from a gaseous atom or ion.

lanthanide contraction.

An effect that causes sixth period elements with filled 4f subshells to be smaller than otherwise expected. The intervention of the lanthanides increases the effective nuclear charge, which offsets the size increase expected from filling the n=6 valence shell. As a consequence, sixth period transition metals are about the same size as their fifth period counterparts.

lanthanide. Compare with actinide and inner transition metals.

Elements 57-70 are called lanthanides. Electrons added during the Aufbau construction of lanthanide atoms go into the 4f subshell.

main group elements.

Elements of the s and p blocks.

metal. metallic. Compare with nonmetal and metalloid.

A metal is a substance that conducts heat and electricity, is shiny and reflects many colors of light, and can be hammered into sheets or drawn into wire. Metals lose electrons easily to form cations. About 80% of the known chemical elements are metals.

nonmetal. (metal,metalloid) non-metal.

A nonmetal is a substance that conducts heat and electricity poorly, is brittle or waxy or gaseous, and cannot be hammered into sheets or drawn into wire. Nonmetals gain electrons easily to form anions. About 20% of the known chemical elements are nonmetals.

periodic law.

The periodic law states that physical and chemical properties of the elements recur in a regular way when the elements are arranged in order of increasing atomic number.

periodic table.

An arrangement of the elements according to increasing atomic number that shows relationships between element properties.

periodic trend.

A regular variation in element properties with increasing atomic number that is ultimately due to regular variations in atomic structure.

period.

Rows in the periodic table are called periods. For example, all of the elements in the second row are referred to as 'second period elements'. All elements currently known fall in the first seven periods.

second ionization energy. (IE,IP) second ionization potential. Compare with first ionization energy, adiabatic ionization energy, vertical ionization energy, electronegativity, and electron affinity.

The energy needed to remove an electron from an isolated +1 ion. The third ionization energy would be the energy required to remove an electron from an isolated +2 ion, and so on.

transition metal. transition element; outer transition element.

An element with an incomplete d subshell. Elements which have common cations with incomplete d subshells are also considered transition metals. Elements with incomplete f subshells are sometimes called "inner transition elements".

Copyright © 1997-2010 by Fred Senese
Comments & questions to fsenese@frostburg.edu
Last Revised 02/23/18.URL: http://antoine.frostburg.edu/chem/senese/101/periodic/glossary.shtml