Stability in Bonding

Combined Elements  Some of the matter around you is in the form of uncombined elements such as copper, sulfur, and oxygen.  When the conditions are right, these and other chemicals will combine to form compounds.  The green coating on the Statue of Liberty is an example of these chemical changes. This new compound is copper sulfate. (copper, sulfur, and oxygen combined)  These new compounds have their own unique properties.  Sodium chloride (table salt) is a compound made from sodium (a shiny, soft, silver metal) and chlorine ( a poisonous greenish-yellow gas).

Formulas  A chemical formula tells what elements a compound contains and the exact number of the atoms of each element in a unit of the compound.  Example: NaCl stands for Sodium Chloride and tells you that there is one atom of sodium and one atom of chlorine in each unit. H 2 O shows that there are two atoms of hydrogen and one atom of oxygen in each unit or molecule of water.

Some Familiar Compounds Familiar NameChemical NameFormula SandSilicon dioxideSiO 2 Cane sugarSucroseC 12 H 22 O 11 LimeCalcium oxideCaO VinegarAcetic acidHC 2 H 3 O 2 Stomach acidHydrochloric acidHCl

Atomic Stability  Atoms combine when the compound formed is more stable than the separate atoms.  However, some of the atoms are stable by themselves.

The Unique Noble Gases  To understand the stability of the noble gases, you must look at electron dot diagrams.  Electron dot diagrams show only the electrons in the outer energy level of an atom.  Ex. Elements in Group 1 have one electron in the outer energy level, Group 2 has two, Group 13 has 3, Group 14 has 4, and so on to Group 18 which has 8.  An atom is chemically stable when the outer energy level is complete.  The noble gases are stable because they each have a complete outer energy level.

Energy Levels and Other Elements  Groups 1, 2, 13, 14, 15, 16, and 17 do not have a full outer energy level, so they are more stable when they are found in compounds.  For example, hydrogen only has one electron in its outer energy level, which means its outer energy level is not complete. This is why there are so many hydrogen-containing compounds found on earth.

Outer Energy Levels- Getting Their Fill  Atoms with partially stable outer energy levels can lose, gain, or share electrons to obtain a stable outer energy level.  They do this by combining with other elements that have partially complete outer energy levels.  This helps them both become stable.  Example: sodium and chlorine

Stability is Reached  Sodium has only one electron in its outer energy level, which is lost to combine with chlorine in sodium chloride.  Now we look to next level down in sodium and see that it is full, so now both elements have a complete energy level and both are now stable.  When atoms gain, lose, or share electrons, an attraction forms between the atoms, pulling them together to form a compound. This attraction is called a chemical bond.  A chemical bond is the force that holds atoms together in a compound.