(Chapter 19)
Stability in Bonding
· Atoms come together to form compounds if the compound is more
stable than the separate atoms
o
When elements
combine chemically to form compounds, they no longer have the same properties
they did as elements
· A chemical
formula is composed of symbols and subscripts
o
Example: H2O
§
Symbols: H =
hydrogen, O = oxygen
§
Subscript: 2 =
means there are 2 hydrogen atoms
· Noble
Gases are more chemically stable
than other elements because they have a complete outer energy level (valence)
o
Elements that do
not have full valences are more stable as compounds
o
Atoms can gain, lose, or share electrons to get a
stable valence
o
A chemical bond is the force that
holds atoms together in a compound
Types of Bonds
Atoms can form bonds by transferring electrons—Ionic
bonds
· Ion—a charged particle that has more or fewer electrons
than protons
o
When an atom
loses an electron, it becomes positively charged
o
When an atom
gains an electron, it becomes negatively charged
· Ionic Bond—the force of attraction opposite charges of
ions
o
The result of an
ionic bond is a neutral compound
o
The sum of the
charges is zero
Atoms can form bonds by sharing electrons—Covalent
Bonds
· Molecules are neutral particles formed as a result of sharing
electrons
· Atoms can form double or triple bonds if they share 2
or 3 electron pairs
· Shared electrons are held more closely to atoms with
the larger nucleus
· A polar
molecule has one end that is slightly positive and one that is slightly
negative but the overall molecule is neutral (ex. H2O)
· In a nonpolar
molecule electrons are shared equally (ex. CH4)
