Chemical Bonds

A.  Why Atoms Combine

1.  Compounds

a.  Compounds are produced when chemical changes occur

b.  The properties of compounds are different from the elements they are made of

2.  Formulas

a.  Chemical shorthand names for compounds

b.  Subscripts show how many atoms there are of each element in a formula

c.  Subscripts after parentheses apply to every element in the parenthesis

3.  Chemical stability

a.  When atoms are chemically stable, they become resistant to change

b.  Atoms become chemically stable when their outermost energy level is filled

c.  All the noble gas elements are stable and do not normally react with other elements to make compounds

d.  Compounds form when elements can become more stable by combining with other elements

e.  Chemical bonds are the forces that hold together the atoms in a compound

B.  Kinds of Chemical Bonds

1.  Ionic bonds

a.  Ions are charged atoms that have lost or gained outer electrons

b.  If atoms lose electrons they become positive ions

c.  When atoms gain electrons they become negative ions

d.  The opposite charges of ions create attractions and make ionic bonds

e.  Ionic bonds tend to be fairly strong

2.  Covalent bonds

a.  Atoms that hold their electrons more tightly may share them with other atoms

b.  Molecules are the larger particles produced by covalent bonds

c.  Electrons are always shared in pairs (orbitals)

d.  Covalent bonds tend to be fairly weak (exception:  network solids)

3.  Polar and nonpolar molecules

a.  Shared electrons are usually not shared equally; one atom attracts them more than the other

b.  This makes certain parts of molecules slightly negative and other parts slightly positive

c.  Nonpolar molecules share electrons equally and have no charged parts

C.  Writing Chemical Formulas and Naming Compounds

1.  Each atom is given an oxidation number to show its combining ability in a compound

2.  The oxidation numbers of atoms in a compound must balance out to zero

3.  Binary compound consist of only two elements

4.  The element with the positive oxidation number is written first in the formula

5.  Naming binary compounds

a.  Write the name of the first element

b.  Write the root of the name of the second element

c.  Add the ending -ide to the root of the second element's name

6.  Polyatomic ions

a.  These are groups of atoms that have a charge and act as a single ion

b.  If more than one are in a formula parentheses must be around the entire group

7.  Hydrates

a.  These are compounds that have water molecules chemically attached to their ions

b.  Anhydrous is the term for these compounds when they do not have the water

c.  To detect whether crystals are hydrates they should be heated; they are if steam is given off