Summarizing the Periodic Table, Compounds and Nomenclature
Summary of lessons so far
The Periodic Table
The discovery of the periodic recurrence of similar properties among the elements led to the formulation of the periodic table, in which the elements are arranged in order of increasing atomic number in rows known as periods and columns known as groups.
Elements in the same group of the periodic table have similar chemical properties. Elements can be classified as metals, metalloids, and nonmetals, or as a main-group elements, transition metals, and inner transition metals. Groups are numbered 1–18 from left to right. The elements in group 1 are known as the alkali metals; those in group 2 are the alkaline earth metals; those in 15 are the pnictogens; those in 16 are the chalcogens; those in 17 are the halogens; and those in 18 are the noble gases.
Molecular and Ionic Compounds
Metals (particularly those in groups 1 and 2) tend to lose the number of electrons that would leave them with the same number of electrons as in the preceding noble gas in the periodic table. By this means, a positively charged ion is formed. Similarly, nonmetals (especially those in groups 16 and 17, and, to a lesser extent, those in Group 15) can gain the number of electrons needed to provide atoms with the same number of electrons as in the next noble gas in the periodic table. Thus, nonmetals tend to form negative ions. Positively charged ions are called cations, and negatively charged ions are called anions. Ions can be either monatomic (containing only one atom) or polyatomic (containing more than one atom).
Compounds that contain ions are called ionic compounds. Ionic compounds generally form from metals and nonmetals. Compounds that do not contain ions, but instead consist of atoms bonded tightly together in molecules (uncharged groups of atoms that behave as a single unit), are called covalent compounds. Covalent compounds usually form from two nonmetals.
Chemical Nomenclature
Chemists use nomenclature rules to clearly name compounds. Ionic and molecular compounds are named using somewhat-different methods. Binary ionic compounds typically consist of a metal and a nonmetal. The name of the metal is written first, followed by the name of the nonmetal with its ending changed to –ide. For example, K2O is called potassium oxide. If the metal can form ions with different charges, a Roman numeral in parentheses follows the name of the metal to specify its charge. Thus, FeCl2 is iron(II) chloride and FeCl3 is iron(III) chloride. Some compounds contain polyatomic ions; the names of common polyatomic ions should be memorized.
Molecular compounds can form compounds with different ratios of their elements, so prefixes are used to specify the numbers of atoms of each element in a molecule of the compound. Examples include SF6, sulfur hexafluoride, and N2O4, dinitrogen tetroxide.
Acids are an important class of compounds containing hydrogen and having special nomenclature rules. Binary acids are named using the prefix hydro-, changing the –ide suffix to –ic, and adding “acid;” HCl is hydrochloric acid. Oxyacids are named by changing the ending of the anion (–ate to –ic and –ite to –ous), and adding “acid;” H2CO3 is carbonic acid.
Glossary of Words
Actinide
inner transition metal in the bottom of the bottom two rows of the periodic table
Alkali metal
element in group 1
Alkaline earth metal
element in group 2
Binary acid
compound that contains hydrogen and one other element, bonded in a way that imparts acidic properties to the compound (ability to release H+ ions when dissolved in water)
Binary compound
compound containing two different elements.
Chalcogen
element in group 16
Covalent bond
attractive force between the nuclei of a molecule’s atoms and pairs of electrons between the atoms
Covalent compound
(also, molecular compound) composed of molecules formed by atoms of two or more different elements
Group
vertical column of the periodic table
Halogen
element in group 17
Inert gas
(also, noble gas) element in group 18
Inner transition metal
(also, lanthanide or actinide) element in the bottom two rows; if in the first row, also called lanthanide, or if in the second row, also called actinide
Ionic bond
electrostatic forces of attraction between the oppositely charged ions of an ionic compound
Ionic compound
compound composed of cations and anions combined in ratios, yielding an electrically neutral substance
Lanthanide
inner transition metal in the top of the bottom two rows of the periodic table
Main-group element
(also, representative element) element in columns 1, 2, and 12–18
Metal
element that is shiny, malleable, good conductor of heat and electricity
Metalloid
element that conducts heat and electricity moderately well, and possesses some properties of metals and some properties of nonmetals
Molecular compound
(also, covalent compound) composed of molecules formed by atoms of two or more different elements
Monatomic ion
ion composed of a single atom
Noble gas
(also, inert gas) element in group 18
Nomenclature
system of rules for naming objects of interest
Nonmetal
element that appears dull, poor conductor of heat and electricity
Oxyacid
compound that contains hydrogen, oxygen, and one other element, bonded in a way that imparts acidic properties to the compound (ability to release H+ ions when dissolved in water)
Oxyanion
polyatomic anion composed of a central atom bonded to oxygen atoms
Period
(also, series) horizontal row of the periodic table
Periodic law
properties of the elements are periodic function of their atomic numbers.
Periodic table
table of the elements that places elements with similar chemical properties close together
Pnictogen
element in group 15
Polyatomic ion
ion composed of more than one atom
Representative element
(also, main-group element) element in columns 1, 2, and 12–18
Series
(also, period) horizontal row of the period table
Transition metal
element in columns 3–11
This lesson is part of:
Atoms, Molecules and Ions