science

this

100

a table of the chemical elements arranged in order of atomic number, usually in rows, so that elements with similar atomic structure (and hence similar chemical properties) appear in vertical columns.

periodic table

200

a length or portion of time.

period

300

a number of people or things that are located close together or are considered or classed together.

group

400

1. a law stating that the elements, when listed in order of their atomic numbers (originally, atomic weights), fall into recurring groups, so that elements with similar properties occur at regular intervals.

   
   

periodic law

500

1. a unit of mass used to express atomic and molecular weights, equal to one-twelfth of the mass of an atom of carbon-12. It is equal to approximately 1.66 x 10-27 kg.

   
   

atomic mass unit

is

100

a solid material that is typically hard, shiny, malleable, fusible, and ductile, with good electrical and thermal conductivity (e.g., iron, gold, silver, copper, and aluminum, and alloys such as brass and steel).

metals

200

1. any of the set of metallic elements occupying a central block (Groups IVB–VIII, IB, and IIB, or 4–12) in the periodic table, e.g., iron, manganese, chromium, and copper. Chemically they show variable valence and a strong tendency to form coordination compounds, and many of their compounds are colored.

   
   

transition metals

300

an element or substance that is not a metal.

nonmetals

400

an element (e.g. arsenic, antimony, or tin) whose properties are intermediate between those of metals and solid nonmetals or semiconductors.

metalloids

500

a single electron or one of two or more electrons in the outer shell of an atom that is responsible for the chemical properties of the atom.

valence electrons

science

100

any of the elements lithium, sodium, potassium, rubidium, cesium, and francium, occupying Group IA (1) of the periodic table. They are very reactive, electropositive, monovalent metals forming strongly alkaline hydroxides.

alkali metals

200

any of the elements beryllium, magnesium, calcium, strontium, barium, and radium, occupying Group IIA (2) of the periodic table. They are reactive, electropositive, divalent metals, and form basic oxides which react with water to form comparatively insoluble hydroxides.

alkaline earth metals

300

any of the elements fluorine, chlorine, bromine, iodine, and astatine, occupying group VIIA (17) of the periodic table. They are reactive nonmetallic elements that form strongly acidic compounds with hydrogen from which simple salts can be made.

halogens

400

any of the gaseous elements helium, neon, argon, krypton, xenon, and radon, occupying Group 0 (18) of the periodic table. They were long believed to be totally unreactive but compounds of xenon, krypton, and radon are now known.

noble gases