Mendeleev  -- devised the 1st periodic table

-- organized the elements based on increasing atomic mass, but the
modern periodic table is based on increasing atomic number

link to periodic table (local file)

link to Los Alamos National Laboratory's Chemistry Division educational periodic table link

[Organization of the Periodic Table]

family  (group)

-- vertical columns of the periodic table
-- all elements in a family have similar properties
-- all elements in a family have the same number of valence electrons

valence electrons  -- electrons in the outermost energy level of the atom

period (row) -- horizontal rows of the periodic table which are arranged on the basis
                        of increasing atomic number

[Interpreting Elemental Symbols]
 

              35
       Cl
17

Note:  The numbers be arranged differently on different tables.

atomic number -- small number --- number of protons  (17 in the example above)

atomic mass -- larger number -- number of protons + neutrons

Note that atomic masses are often expressed as decimals, while the atomic number is always
a whole number!

Some Major Element Categories

I.   Metals
 

• atoms of metals tend to lose their electrons easily to other atoms .. this means they corrode easily
• group IA and IIA metals (alkali and alkali earth metals) are the most chemically active
• many have luster or shine
• most metals are good conductors of heat and electricity
• most metals are ductile  (can be drawn into thin wires)
• most metals are malleable (can be shaped with a hammer)
• most metals are high in density
• most metals have high melting points ... mercury Hg is an exception as it is liquid at room temperature
• metals make up about 2/3 of the elements and are found on the left side of the zig-zag line of the periodic table

• tend to take electrons from other atoms -- the group 17 gases called halogens are the most reactive
• group 18 gases (called noble gases) are almost completely unreactive
• are brittle and break easily (those that are not gases)
• have no luster
• most are low in density and have low boiling points
• tend to be poor conductors
• found on the right hand side of the zig-zag line of the periodic table

• found along the zig-zag line of the periodic table
• have characteristics of both metals and nonmetals
• have properties part way between those of metals and nonmetals
• include the elements boron, silicon, germanium, arsenic, antimony, tellurium, polonium, and astatine