PS

PS-4.3 Illustrate the fact that ions attract ions of opposite charge from all directions and form crystal lattices.

Metals are atoms that have 3 or fewer valence electrons. metal atoms tend to lose electrons to become stable.

Note that group 1 metals have one electron in the outer energy level; Group 1 metals will tend to lose one electron and become an ion with a 1+ charge because the number of electrons is now one less that the number of positive protons.

Note that group 2 metals have two electrons in the outer energy level; Group 2 metals will tend to lose two electrons and become an ion with a 2+ charge because the number of electrons is now two less than the number of positive protons.

Generally, nonmetals have atoms with 5, 6, 7 or 8 valence electrons. The chart below is a summary of Groups 15 through Group 18 nonmetals.

Atoms are stable with 8 valence electrons...Except for Helium. It is stable with a filled first level containing 2 valence electrons. These elements are stable. Their valence level is filled.

Group 16 atoms have 6 electrons in the outside energy level; Group 16 atoms such as oxygen become stable by gaining two electrons and become ion with a 2- charge because they now have two more negative electrons than positive protons.

Group 17 atoms have seven electrons in the outside energy level; Group 17 atoms such as chlorine can become stable most easily by gaining one electron to become an ion with a 1- charge because they now have one more negative electron than positive protons.

Remember! Ionic bonds form when positively charged metal ions attract negatively charged nonmetal ions. ( Oppositely charged ions attract! )

When oppositely charged ions attract each other to form ionic bonds, the oppositely charged ions can surround each other and form a crystal lattice. Within the crystal, ions cluster together in a pattern that will cancel the net charge of the ions. This often results in a regular repeating pattern that is expressed outwardly as a crystal shape. Salt crystals are cubic because the outward shape is controlled by the arraignment of the Sodium and Chlorine ions.

In diagram "D" below, a Sodium atom and a Chlorine atom form a formula unit, NaCl. Note that the Sodium atom is a metal from Group 1, and the Chlorine atom is a nonmetal from Group 17. The formula unit results from the transfer of a single valence electron from the Sodium atom to the Chlorine atom: Na1+ + Cl1- NaCl.

Diagram "E" below, shows what happens when formula units of Sodium Chloride cluster together in a pattern that will cancel the net charge of the ions. In this case the clusters of ions forms a cubic lattice. Diagram "F" shows a Hexagonal arraignment of ions forming a Hexagonal crystal lattice. Click Here to see some other interesting crystal shapes.