The more exposure students have to the Periodic Table
the more familiar they will become with the elements. The Periodic Table is
arranged so that nonmetals are on the right side of the chart and metals on
the center and to the left. The color coding on the chart indicates this
classification. Note the right-descending "staircase line"
separating nonmetal and metals. The elements to the immediate left of the
"staircase line" are called "semi-metals" or
"metalloids" because they can behave chemically as both metals or
nonmetals. The metallic elements are characterized by a metallic luster and
high electrical and thermal conductivity. The nonmetals may be gases,
liquids or crystalline solids.
An element that has a charge is called an
"ion." Generally, the metals have a positive charge (a positive
ion) and the nonmetals a negative charge (a negative ion). There are several
exceptions to this rule but there is no need to point this out to the
students at this time. A chemical reaction can take place when a positively
charged element meets a negatively charged element.
Minerals are compounds made of elements that have both
negative and positive charges, which combine so that the overall charge
equals zero, making the compound electrically neutral. For example table
salt (the mineral halite) is composed of sodium, which has a +1 charge, and
chlorine, which has a charge of -1. Since there are equal numbers of sodium
and chlorine atoms in halite, the overall charge is zero. We will not be
concerned with balancing charges in this activity, because the main point is
to illustrate that positive and negative elements come together.