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 ClO4–

chlorate ClO3–

chlorite ClO2–

hypochlorite 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+CO3

-22

Ca+2 OH-2Ca( )

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: CrOchromium (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 di = 2tri = 3 tetra = 4penta = 5 hexa = 6hepta = 7 octa = 8nona = 9 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)