BONDING
Chemical bond – force that hold two atoms together
A bond is either the attraction between ions (ionic bond) or the attraction between
the positive nucleus and negative electrons (covalent bond)
Atoms bond to become stable
Stable atoms have a full valence (like noble gases)
Ex. Na – lose one electron becomes like Ne
O – gain two electrons becomes like Ne
Ionic Bonds – electrostatic force that holds opposite charged ions together
Atoms can become ions to have full valence (like noble gases)
cation – lose electrons
anion – gain electrons
Stable octet – full valence (8 electrons)
Metals want to have octet like noble gas before them
Nonmetals want octet like noble gas after them
(transition metals form +2 or +3 ions)
Cation bonds with anion to make ionic compound
Ionic compounds – form a repeating pattern of + and – (salt crystal)
Crystal lattice – structure of an ionic compound
Properties:
high melting / boiling point
brittle
nonconductors as solids but in a liquid break into ions and c
onduct
energy released (exothermic) when ions form ionic
compounds
Lewis Dot Structure for ionic compounds:
Put valence electrons around symbol
Use arrows to move electrons so all atoms either have 8 or 0 valence electrons
Write formula based on how many atoms used
Writing Ionic Formulas
First find the charge of the ions you are bonding
Metals always cations (lose electrons), nonmetals always anions (gain
electrons)
Transition metals can be more than one ion – a roman numeral will be
after symbol to know which ion it is. Ex. Iron III = Fe+3
Use as many of each ion as necessary to make overall charge zero
Ex. Lithium sulfide = Li+1 S-2  Li2S
If you have polyatomic ions, you must put ion in parenthesis and the subscript
applies to both atoms in the ion. Ex. 2 sulfate ions = [SO4]2
+1 +2
+2 or +3
+3
-3 -2 -1
Metallic Bonds
Metals can join together because they form cations and will attract electrons from
each other
Metals share the electrons with each other
Metal properties
Most have high melting / boiling point
Ductile
Malleable
Good conductors
Alloy – mixture of metals
Covalent Bonds
Two or more nonmetals share electrons
Atoms share electrons to have stable octet (8 each)
Covalently bonded atoms make a molecule
Diatomic molecule – two of same atom join together (H2, O2)
Atoms always share pairs of electrons
Will share as many pairs as necessary to make atoms stable
Lewis structures
Use dots for valence electrons
Shared pair of electrons becomes a line connecting the two atoms
Share as many pairs as necessary to make stable octet for each atom
Ex. O2
H2
:O=O:
H-H