Transcript chapter five notes97-2002

TYPES OF COMPOUNDS
Chemical Family Resemblances
Binary salts
Binary salts are made of a metal and a
nonmetal – only two different elements.
Examples: NaCl, MnO2
 Binary salts are named with the name of the
metal first, then the name of the nonmetal
with the “-ide” ending.
Example: K2O
potassium oxide

FORMULAS
 The formula unit is the simplest ratio of
ions in the salt.
Ga2O3
2:3 ratio of gallium atoms to oxygen atoms
2 gallium atoms and 3 oxygen atoms make
one formula unit
formulas
 Electrons and charge are conserved
in a
formula unit.
– 2 gallium atoms have a total of 6 valence
electrons and no charge
– 3 oxygen atoms have a total of 18 valence
electrons and no charge
– so gallium oxide (Ga2O3) has 18+6=24
valence electrons and no charge
conservation
 Conservation of
electrons and charge in
gallium sulfide (Ga2S3)
conservation
oxidation numbers
 Oxidation
number of an ion is equal to
the charge on an ion after it gains or loses
electrons.
 All atoms gain or lose electrons to try to
attain a noble gas configuration (8
valence electrons)
 Noble gases have no oxidation numbers
oxidation numbers
 Metals
– lose all valence electrons,
positive (+) oxidation numbers
 Metals lose electrons so as to expose full
valence shell in next lower level
– Alkali metals and hydrogen are +1
– Alkaline earths are +2
– Aluminum and friends are +3
oxidation states
– Tin and lead are +2 or +4
– Transition metals vary
 Nonmetals
– gain electrons, negative (-)
oxidation numbers
 Enough electrons are gained to complete
the valence shell
– Oxygen is always –2, and sulfur is –2 unless
with oxygen
ternary salts
– Halogens are –1 unless with oxygen
– Nitrogen and phosphorus are –3 unless with
oxygen or halogens
 Ternary salts are composed of
more than
two elements
 Ternary salts contain polyatomic ions
– Polyatomic ions contain more than one atom
example: CO3-2 carbonate
polyatomic ions
 Polyatomic anions
have a (-) charge, and
polyatomic cations a (+) charge
 Polyatomic ions act as a unit – the
subscripts of the formula may not be
changed
 Names and formulas
– Most names end in “-ate” or “-ite”, which
means the ion contains oxygen
naming polyatomic ions
– Examples: sulfate (SO4-2), sulfite (SO3-2)
– The ending and prefix (if present) indicate
the relative number of oxygen atoms in the
formula.
perchlorate
chlorate
chlorite
hypochlorite
ClO4–
ClO3–
ClO2–
ClO–
polyatomic cations
 The “-ium”
ending means a positive ion
(hydronium, H3O+, and ammonium,
NH4+)
 Multiple ions are indicated by
parentheses and a subscript
– Example: magnesium hydroxide is Mg(OH)2
– Ammonium sulfide: (NH4)2S
formulas with
polyatomic ions
 Formulas are
made the same way as the
binary salts, with the criss-cross method
+
Na 2
CO3
-2
+2 (OH-)
CaCa
2
Naming ternary salts
 Ternary salts are
named with the metal
name first, then the name of the
polyatomic ion
K3PO4
potassium phosphate
Transition metal salts
 Many transition and
“other” metals have
more than one oxidation number
 These numbers are found on some
periodic tables
 Metals to know: Fe (+2, +3), Cu (+1, +2),
Ag (+1), Zn (+2), Sn (+2, +4), Pb (+2, +4),
Bi (+3, +5)
transition metal salts
 Oxidation
number of transition metal is
indicated by a Roman numeral in
parentheses
 FeCl3 is iron (III) chloride
 Name these: CrO chromium (II) oxide
Cr2O3
chromium (III) oxide
CrO3
chromium (IV) oxide
transition metal salts
 The Roman
numeral is not needed if
there is only one oxidation state for the
metal (i.e. Zn, Ag, Sc)
 The Roman numeral is also used for
“other” metal salts like tin (II) fluoride
(SnF2, formerly used in toothpaste)
 Transition metal salts are often brightly
colored
hydrates
 Hydrates are salts that have water
incorporated into the crystal structure
 The water is usually associated with the
cation
 The number of water molecules in the
crystal are specified in the formula
MgCl2. 6H2O
hydrates
 The dot means they are
not chemically
bonded
 Names of hydrates – “hydrate” plus a
prefix is added to the salt name
MgCl2. 6H2O
is magnesium chloride hexahydrate
 Prefix indicates the number of water
molecules
hydrate prefixes
mono = 1
tri = 3
penta = 5
hepta = 7
nona = 9
di = 2
tetra = 4
hexa = 6
octa = 8
deca = 10
Formation of hydrates
 Hydrates can
be formed when certain
salts are crystallized from water.
 Example – CuSO4. 5H2O {copper (II)
sulfate pentahydrate}
 Hygroscopic compounds become
hydrates by taking water from the air.
Formation of Hydrates
 Example
– sodium carbonate becomes
sodium carbonate decahydrate
(Na2CO3. 10H2O)
 Deliquescent compounds take enough
water from the air to form concentrated
solutions – examples: calcium chloride
(CaCl2), sodium hydroxide (NaOH)