Chemistry - Atoms, Molecules and Ions

anion

a negatively charged ion

atom

an extremely small particle of matter that retains its identity during chemical reactions

atomic mass unit

a mass unit equal to exactly one twelfth the mass of a carbon-12 atom

atomic number

the number of protons in the nucleus of an atom

atomic symbol

a one- or two-letter notation used to represent an atom corresponding to a particular element

atomic theory

an explanation of the structure of matter in terms of different combinations of very small particles

binary compound

a compound composed of only two elements

catalyst

a substance that increases the rate of reaction without being consumed in the overall reaction

cation

a positively charged ion

chemical equation

the symbolic representation of a chemical reaction in terms of chemical formulas

chemical formula

a notation that uses atomic symbols with numerical subscripts to convey the relative proportions of atoms of the different elements in a substance

chemical nomenclature

the systematic naming of chemical compounds

compound

a type of matter composed of atoms of two or more elements chemically combined in fixed proportions

element

a type of matter composed of only one kind of atom

formula unit

the group of atoms or ions explicitly symbolized in the formula

fractional (isotopic) abundance

the fraction of the total number of atoms that is composed of a particular isotope

group

the elements in any one column of the periodic table

hydrate

a compound that contains water molecules weakly bound in its crystals

hydrocarbons

compounds containing only carbon and hydrogen

inorganic compounds

compounds composed of elements other than carbon

ion

an electrically charged particle obtained from an atom or a chemically bonded group of atoms by adding or removing electrons

ionic compound

a compound composed of cations and anions

isotopes

atoms whose nuclei have the same atomic number but different mass numbers

law of multiple proportions

when two elements form more than one compound, the masses of one element in these compounds for a fixed mass of the other element are in ratios of small whole numbers

mass number

the total number of protons and neutrons in a nucleus

metalloid

an element having both metallic and nonmetallic properties

molecular formula

a chemical formula that gives the exact number of different atoms of an element in a molecule

molecule

a definite group of atoms that are chemically bonded together

monoatomic ion

an ion formed from a single atom

monomer

the small molecules that are linked together to form a polymer

nonmetal

an element that does not exhibit the characteristics of a metal

nucleus

the atom’s central core where the mass of the atom is concentrated

nuclide

a particular atom characterized by a definite atomic number and mass number

organic compounds

compounds that contain carbon combined with other elements, such as hydrogen, oxygen, and nitrogen

oxoacid

an acid containing hydrogen, oxygen, and another element (often called the central element)

period

the elements in any one horizontal row of the periodic table

periodic table

a tabular arrangement of elements in rows and columns, highlighting the regular repetition of properties of the elements

polyatomic ion

an ion consisting of two or more atoms chemically bonded together and carrying a net electric charge

polymer

a very large molecule made up of a number of smaller molecules repeatedly linked together

product

a substance that results from a chemical reaction

reactant

a starting substance in a chemical reaction