Transcript ionic vs covalent notes

Chapter 5
• Combined elements
– Compounds = unique properties from the
elements that make them up.
– NaCl for example
• Na = shiny, soft, silvery, metal that reacts
violently with water
• Cl = a poisonous greenish yellow gas
• NaCl = table salt
Formulas
• Chemical formula = tells what
elements a compound contains and the
exact number of atoms of each element
in a unit of that compound.
• Example: N2O = (2 nitrogen atoms 1
oxygen atom)
Atomic Stability
• Why do atoms form compounds?
– The electric forces between electrons and
protons (opposites) cause compounds to
form
Atomic Stability
• An atom is chemically stable when its
outermost energy level has the
maximum number of electrons.
• For H and He …2 electrons equal stable
• For all other elements…8 electrons =
stable
How do outer levels get their
fill?
• Atoms with partially stable outer energy
levels can lose, gain, or share electrons
to obtain stable outer energy levels
• Ion = an charged particle because it
has more or less electrons than protons
• They do this by combining with other
atoms
Chemical Bond
• Chemical bond = the force that holds
atoms together in a compound
• The force occurs when atoms gain,
lose, or share electrons…an attraction
forms that pulls the atoms together to
from a compound
• What holds bonded atoms together?
– When their valence electrons interact
(outer most shell)
– Atoms join so that each atom has a full
outermost energy level
Ionic Bonds
• Formed by the transfer of electrons
• Ex) Na+ bonds w/ Cl- = NaCl
•
•
•
•
Each atom loses or gains electrons
Metals bond with nonmetals
Melting point = high
Ionic bonds tend to conduct electricity
Ionic Bond
Covalent Bonds
• Bond formed when elements share one
or more electrons.
• Ex) Cl- bonds with a Cl- = Cl2
EX) C+2 bonds w/ O-2 = CO (carbon
monoxide)
• Nonmetals combine with nonmetals
• Melting point = low
Ionic and Covalent Bond
Video
Polyatomic Ions
• Can have both ionic and covalent bonds
• Usually groups of covalently bonded atoms
that have lost or gained electrons
• Ex) NaHCO3 (sodium hydrogen carbonate)
NaOH (Sodium Hydroxide)
(NH4)SO4 (ammonium sulfate)
Metallic Bonds
• Bond formed by the attraction between
positively charged metal ions
• Electrons move freely from metal atom
to metal atom
• This is why metals conduct electricity so
well