Copyright Sautter 2003

CHEMICAL FORMULAE*

HOW TO WRITE FORMULAS FROM NAMES AND NAMES

FROM FORMULAS*

* SOME BOOKS USE FORMULAE ENDING IN AE WHICH IS THE LATIN PLURAL INSTEAD OF FORMULAS

TYPE OF COMPOUNDS

• (1) IONIC COMPOUNDS – THOSE CONSISTING PRIMARILY OF METALS COMBINED WITH NONMETALS

• (A METAL COMBINED WITH A NONMETAL IS CALLED A SALT. SODIUM CHLORIDE OR “TABLE SALT” IS NOT THE ONLY SALT, THERE ARE MANY DIFFERENT KINDS OF SALTS. IT HOWEVER IS ONE OF THE MOST COMMON SALTS.)

• (2) MOLECULAR COMPOUNDS – THOSE CONSISTING OF NONMETALS

WHAT ARE IONS?CHARGED ATOMS OR GROUPS OF ATOMS

THERE ARE TWO KINDS OF IONS, POSITIVE AND NEGATIVE

• POSITIVE IONS ARE ATOMS OR GROUPS OF ATOMS WITH MISSING ELECTRONS

• THESE IONS USUALLY CONSIST OF METALS

• THEY ARE ALSO CALLED CATIONS

• NEGATIVE ION ARE ATOMS OR GROUPS OF ATOMS WITH EXTRA ELECTRONS

• THESE IONS USUALLY CONSIST OF NONMETALS

• THEY ARE ALSO CALLED ANIONS (NOT DOG IONS AS YOU MIGHT EXPECT !!)

SOME COMMON CATIONS (POSITIVE IONS)

• NAME• SODIUM

• ZINC

• POTASSIUM

• CALCIUM

• MAGNESIUM

• COPPER II (CUPRIC)

• IRON II (FERROUS)

• IRON III (FERRIC)• AMMONIUM*

*ONE OF THE FEW POLYATOMIC CATIONS

• FORMULAS• Na+1

• Zn+2

• K+1

• Ca+2

• Mg+2

• Cu+2

• Fe+2

• Fe+3

• NH4+1

SOME COMMON ANIONS (NEGATIVE IONS)

• NAMES• CHLORIDE

• SULFIDE

• BROMIDE

• SULFATE

• SULFITE

• NITRATE

• NITRITE

• CARBONATE

• CHROMATE

• FORMULAS• Cl-1

• S-2

• Br-1

• SO4-2

• SO3-2

• NO3-1

• NO2-1

• CO3-2

• CrO4-2

SOME RULES REGARDING CATIONS (POSITIVE IONS)

• IONS FROM COLUMN I (ALKALI METALS) ON THE PERIODIC TABLE ARE ALWAYS +1

• IONS FROM COLUMN II (ALKALINE EARTH METALS) ON THE PERIODIC TABLE ARE ALWAYS +2

• IONS FROM COLUMN II (THE ALUMINIUM GROUP) ON THE PERIODIC TABLE ARE +3

• THE TRANSITIONAL METALS HAVE VARIABLE CHARGES RANGING FROM +1 TO +5

• EXAMPLES:

• COLUMN I COLUMN II

• Na+1 Ca+2

• K+1 Mg+2

• etc. etc.

• COLUMN III

• Al+3

• Ga+3

• TRANSITIONAL METALS

• Cu+2

• Fe+2

• Cr+3

TRANSITIONAL METALS WITH VARIABLE CHARGE STATES

• SOME TRANSITIONAL METALS CAN EXSIST AS IONS IN TWO DIFFERENT CHARGE STATES. SOME OF THESE ELEMENTS ARE COPPER, TIN, IRON, COBALT, LEAD, MERCURY, CHROMIUM AND MANGANESE.

• * THESE VARIABLE CHARGES HAVE NO PATTERN AND MUST BE MEMORIZED

• EXAMPLES:• COPPER +1 OR +2• TIN +2 OR +4• IRON +2 OR +3• COBALT +2 OR +3• LEAD +2 OR +4• MERCURY +1 OR +2• CHROMIUM +2 OR +3• MANGANESE +2 OR +3• * THE SAME ATOM WITH

DIFFERENT CHARGE STATES ARE DESIGNATED USING ROMAN NUMERIALS SUCH AS COPPER I FOR Cu+1 OR LEAD II FOR Pb+2

RULES REGARDING FORMULAS AND NAMES FOR ANIONS (NEGATIVE IONS)

• ANIONS FROM COLUMN VII (HALOGENS) ARE CHARGED –1

• ANIONS FROM COLUMN VI (OXYGEN GROUP) ARE CHARGED –2

• ANIONS FROM COLUMN V (NITROGEN GROUP) ARE CHARGED –3 WHEN THE IONS ARE SINGLE ATOMS (MONATOMIC)

• EXAMPLES:

• COLUMN VII

• Cl-1

• Br-1

• COLUMN VI

• S-2

• O-2

• COLUMN V

• N-3

P-3

NAMING MONATOMIC (SINGLE ATOM) ANIONS

• ANIONS THAT CONSIST OF ONLY ONE ATOM END IN ALWAYS “IDE”.

• ANIONS THAT CONSIST OF MORE THAN ONE ATOM BUT CONTAIN NO OXYGEN ALSO END IN “IDE”

• THE HYROXIDE ION IS AN EXCEPTION IN THAT IT CONTAINS OXYGEN AND POLYATOMIC BUT ENDS IN “IDE”

• CHLORIDE Cl-1

• SULFIDE S-2

• NITRIDE N-3

• CYANIDE CN-1

• THIOCYANIDE SCN-1

• HYDROXIDE OH-1

POLYATOMIC IONS ARE THOSE THAT CONSIST OF MORE THAN ONE ATOM. MOST ARE ANIONS.

• POLYATOMIC IONS THAT CONTAIN OXYGEN END IN “ATE” OR “ITE”

• ONCE POLYATOMIC IONS ENDING IN “ATE” ARE KNOWN, IONS OF SIMILAR COMPOSITION BUT DIFFERING BY ONE LESS OXYGEN ATOM END IN “ITE”

• EXAMPLES:• SULFATE • SO4

-2

• SULFITE HAS ONE LESS OXYGEN ATOM

• SO3-2

• NITRATE• NO3

-1

• NITRITE HAS ONE LESS OXYGEN ATOM

• NO2-1

POLYATOMIC IONS ARE THOSE THAT CONSIST OF MORE THAN ONE ATOM. MOST ARE ANIONS.

• Polyatomic anions which contain one more oxygen than the “ate” form are given the prefix “per”

• ClO3-1 is chlorate, ClO4

-1 is perchlorate

• Polyatomic anions which contain one less oxygen than the “ite” form are given the prefix “hypo”

• ClO2-1 is chlorite, ClO-1 is hypochlorite

FORMULAS OF IONIC COMPOUNDS(CATIONS ARE ALWAYS NAMED FIRST FOLLOWED BY THE

NAME OF THE ANION IN THE COMPOUND)

• IONIC SALTS ARE FORMED WHEN CATIONS COMBINE WITH ANIONS

• THE NET CHARGE ON ALL SALTS MUST BE ZERO WHICH MEANS ALL THE POSITIVE CHARGES ON THE CATIONS MUST BALANCE ALL THE NEGATIVE CHARGE ON THE ANIONS

• EXAMPLE:

• WHEN SODIUM CHLORIDE IS FORMED FROM A POSITIVE SODIUM ION AND A NEGATIVE CHLORIDE ION, JUST ONE SODIUM WITH A +1 CHARGE IS REQUIRED TO BALANCE JUST ONE CHLORIDE WITH A –1 CHARGE. SO THE FORMULA IS JUST NaCl.

WHAT ABOUT FORMULAS FOR COMPOUNDS WHEN THE POSITIVE AND NEGATIVE CHARGES DON’T

EXACTLY BALANCE

• ZINC CHLORIDE CONSISTS OF ZINC WITH A +2 CHARGE AND CHLORIDE WITH A –1 CHARGE.

• IN ORDER TO BALANCE THE CHARGES, ONE ZINC MUST COMBINE WITH TWO CHLORIDES. THE FORMULA FOR ZINC CHLORIDE IS ZnCl2.

• (+2) + ( 2 x (-1)) = 0

• IRON III SULFIDE CONSISTS OF TWO IRON ATOMS AND THREE SULFUR ATOMS.

• EACH IRON III ION HAS A +3 CHARGE AND EACH SULFIDE ION HAS A –2 CHARGE. THE FORMULA FOR IRON III SULFIDE IS Fe2S3.

• (2 x ( +3)) + (3 x (-2)) = 0

IONIC COMPOUNDS CONTAINING POLYATOMIC IONS (CATIONS AND ANIONS)

• LEAD II NITRATE CONSISTS OF ONE LEAD II ION WITH A +2 CHARGE AND TWO NITRATE IONS EACH WITH A –1 CHARGE.

• IN ORDER TO BALANCE THE CHARGES, ONE LEAD II MUST COMBINE WITH TWO NITRATES. THE FORMULA FOR LEAD II NITRATE IS Pb(NO3)2.

• ( +2) + (2 x (-1)) = 0

• AMMONIUM PHOSPHATE CONSISTS OF THREE AMMONIUM IONS EACH WITH A +1 CHARGE AND ONE PHOSPHATE WITH A –3 CHARGE.

• IN ORDER TO BALANCE THE CHARGES, THREE AMMONIUM IONS MUST COMBINE WITH ONE PHOSPHATE. THE FORMULA FOR AMMONIUM PHOSPHATE IS (NH4)3PO4.

• (3 x (+1)) + (-3) = 0

The positive ioncharge without itssign becomes thesubscript of the

negative ion

The negative ion charge without itssign becomes the subscript of the

positive ion1 (+3) + 3(-1) = 0

FORMULAS AND NAMES FOR MOLECULAR COMPOUNDS (COMPOUNDS CONSISTING OF ONLY

NONMETALS, NOT IONS)

• NONMETALS ARE THE ELEMENTS ON THE RIGHT SIDE OF THE PERIODIC TABLE.

• WHEN NAMING COMPOUNDS, PREFIXES ARE USED TO TELL THE NUMBER OF EACH KIND OF ATOM.

• PREFIXES USED

• MONO = 1

• DI = 2

• TRI = 3

• TETRA = 4

• PENTA = 5

• HEXA = 6

• HEPTA = 7

• OCTA = 8

NAMES AND FORMULAS OF MOLECULAR COMPOUNDS

• SULFUR DIOXIDE CONSISTS OF ONE SULFUR ATOM (NO PREFIX IS USED) AND TWO (DI) OXYGEN ATOMS. BOTH SULFUR AND OXYGEN ARE NONMETALS. THE FORMULA FOR SULFUR DIOXIDE IS SO2

• DINITROGEN PENTOXIDE CONSISTS OF TWO NITROGEN ATOMS (DI) AND FIVE OXYGEN ATOMS (PENTA). BOTH NITROGEN AND OXYGEN ARE NONMETALS. THE FORMULA FOR DINITROGEN PENTOXIDE IS N2O5.