9 nomenclature of inorganic compounds
TRANSCRIPT
Nomenclature of Inorganic Compounds
Overview
• A lot of compounds are available nowadays.
• Remembering their names would be quite difficult.
• There must be a systematic method of naming (a technique that provides relationship of names with its formula) should be used.
Chemical formula
• It is a representation, which is used to denote one molecule of pure substance
Chemical formula
• It indicates the relative amount of atoms of each element in a molecule, which consists of symbols of the elements composing the pure substance and subscripts denoting relative number of atoms of each element in a unit particle or molecule of the element of compound.
OXIDATION NUMBERS
• Oxidation number or oxidation state is an apparent charge of an atom in a compound when electrons are transferred from one atom to another to form ions.
OXIDATION NUMBERS
• This set of whole numbers (sometimes positive and in other cases, negative) are very useful for predicting the formulas of the compounds, classifying them, comparing the chemical properties of the elements and describing chemical reactions
Rules for Assigning Oxidation Numbers/States 1. The oxidation numbers of an
element in the free or uncombined state is always zero.
• Example: Cu0, Si0, Mg0
Rules for Assigning Oxidation Numbers/States 2. The oxidation numbers of
monoatomic ion is the same as the charge on the ion.
• The group of numbers in the periodic table will help us remember the oxidation numbers.
Rules for Assigning Oxidation Numbers/States • There are two important general
observations:– A common oxidation number of all
metals is positive and is equal to its group number.
– A common oxidation number of all nonmetals is negative and is equal to the group number minus 8.
Common Oxidation States of Common Elements
GROUP NO.
OXIDATION NUMBERS
EXAMPLES
IA +1 Na+, Li+, Ag+1
IIA +2 Mg2+, Ba2+, Zn2+
IIIA +3 Al3+, B3+
IVA +4/-4 C4+
VA -3 N3-, C4-, Si4+
VIA -2 O2-
VIIA -1 F-, Cl-
Notes
• An element with positive oxidation number is a positive ion called CATION and an element with negative oxidation number is a negative ion called ANION.
Notes
• There are elements that have more than one oxidation numbers.
• Generally, they are the transition elements.
Common Oxidation Numbers of Common Transition Elements
OXID NO.
FORMULA NAME OF THE ION
OXID NO.
FORMULA NAME OF THE ION
Cr2+ chromous/chromium (II) Cu2+ cupric/copper (II)
Cr3+ chromic/chromium (III) Hg+ mercurous/mercury (I)
Mn2+ manganous/manganese (II)
Hg2+ mercuric/mercury (II)
Mn4+ manganic/manganese (IV)
Sn2+ stannous/tin(II)
Fe2+ ferrous/iron (II) Sn4+ stannic/tin (IV)
Fe3+ ferric/iron (III) Pb2+ plumbous/lead (II)
Co2+ cobaltous/cobalt (II) Pb4+ plumbic/lead (IV)
Co3+ cobaltic/cobalt (III) H+ hydrogen/hydronium
Cu+ cuprous/copper (I) H- hydride*H is not a transition element.
Rules for Assigning Oxidation Numbers/States 3. The algebraic sum of the oxidation
numbers for all the atoms in the formula of a compound is zero.
ex. Mg2+Br2-
+2 + (-1)(2) = 0
Rules for Assigning Oxidation Numbers/States 4. The sum of the oxidation numbers
of the atoms in a polyatomic ion must be equal the charge of the ion.
Common Polyatomic Ions
Monovalent IonsNH4
+ Ammonium HCO3- Bicarbonate
C2H3O2- Acetate NO2
- Nitrite
ClO- Hypochlorite NO3- Nitrate
ClO2- Chlorite MnO4
- Permanganate
ClO3- Chlorate HSO4
- Bisulfate
ClO4- Perchlorate HSO3
- Bisulfite
CN- Cyanide CNO- Cyanate OH- Hydroxide CNS- Thiocyanate
Common Polyatomic Ions
Divalent IonsCO3
2- Carbonate SO42- Sulfate
CrO42- Chromate S2O3
2- Thiosulfate
Cr2O72- Dichromate HPO4
2- Biphosphate
C2O42- Oxalate SiO3
2- Silicate
SO32- Sulfite ZnO2
2- Zincate
Common Polyatomic Ions
Trivalent IonsPO3
3- Phosphite
PO43- Phosphate
Polyvalent IonsP2O7
4- Pyrophosphate
Rules for Assigning Oxidation Numbers/States
5. Some common oxidation numbers:
– Hydrogen has usually +1, except in hydrides (ionic compounds with IA and IIA), it has –1.
– Oxygen has usually –2, except in peroxides, such as H2O2, and Na2O2, it has –1.
– Aluminum (Group IIIA) has +3: Zinc (Group IIB) has +2 and Silver (Group IB) has +1.
Rule in Writing Formulas
General Method
• The symbol of the cation is written first followed by the symbol of the anion then apply the criss-cross method.
Rule in Writing Formulas
• Metals, nonmetals and inert gases have their formulas the same as their symbols.
Example: Calcium CaMagnesium Mg
Rule in Writing Formulas
• Active gaseous elements are written correctly by taking two atoms of the elements since these are diatomic molecules.
Examples: Oxygen O2
Hydrogen H2
Rule in Writing Formulas
• Compounds: Write the symbol of the positive element or positive radical with their oxidation number first, then followed by the negative element or negative radical with their oxidation number also. The algebraic sum of the oxidation numbers must be equal zero so that the compound will be neutral.
Rule in Writing Formulas
• When the positive oxidation numbers and the negative oxidation numbers are the same, the formula is the same as it stands.
Example: K+Br- KBrSr+2O-2 SrO
Rule in Writing Formulas
• When the positive oxidation number and the negative oxidation numbers are not the same, apply the criss-cross rule so that the algebraic sum of the oxidation numbers will be equal to zero.
Example: Al+3S-2 Al2S3
Ca+2Cl- CaCl2
Rule in Writing Formulas
• Whenever a radical in a formula is taken more than once, enclose the radical inside a parenthesis and write the correct subscript after the parenthesis.
Example: K+(Cr2O7)2- K2Cr2O7
Ba+2(OH)-
Ba(OH)2
Examples
• Sodium chloride• Ferrous oxide• Aluminum iodide• Calcium phosphate• Ammonium carbonate
Systematic Naming of Compounds• Binary Compounds• compound which is composed of two
elements
Binary Salts (M + NM)
• For metals with fixed oxidation no.• Rule: name the (+) ion + name
the stem of (-) ion + IDENaI Sodium iodideMgBr2 Magnesium
bromideK3N Potassium nitride
CaO Calcium Oxide
Binary Salts (M + NM)
• For metals with variable oxidation nos.
• Method I: Old or Classical Method
• Rule : name the metal with suffixes –ous or –ic + name of non-metal + IDE
Cu3B Cuprous boride
SnS2 Stannic sulfide
Binary Salts (M + NM)
• For metals with variable oxidation nos.• Method II : Stock or Roman Numeral
Method• Rule : name of metal + (Roman
numeral of the oxid no) + Name of stem of non-metal + IDE
PbBr2 Lead (II) bromide
AuCl3 Gold (III) chloride
Binary Acids (H + NM)
• Dry form (when acid is not dissolved in water)
• Rule: Hydrogen + name of non-metallic element + IDE
HCl Hydrogen chlorideHBr Hydrogen bromide
Binary Acids (H + NM)
• Aqueous Form (when acid is dissolved in water to form an acidic solution)
• Rule: Hydro + name of the non-metal with suffix –ic + acid
HCl(aq) Hydrochloric acid
HBr(aq) Hydrobromic acid
Non-metal + Non-metal
• Greek prefixes are used to indicate the number of atoms in each element present in a molecule of a compound
• Numeric Prefixes1 - mono 4 - tetra 7 - hepta 10 - deca2 - di 5 - penta 8 - octa 11 - undeca3 - tri 6 - hexa 9 - nona 12 - dodeca
Non-metal + Non-metal
• Rule:• Name the more positive element first
and followed by the name of the more negative element
• Use the Greek prefixes listed above, to indicate the number of atoms of each type of element present in the formula of the compound.
Non-metal + Non-metal
• Rule:• The prefix -MONO is often omitted when it
applies to the first element in a compound.• Use the suffix -IDE to the second element.
N2O dinitrogen monoxide
CO carbon monoxide
SO2 sulfur dioxide
CO2 carbon dioxide
Hydrides
• Hydrogen reacts with many metals to form binary compounds called hydrides.
• In these compounds, the hydrogen is more electronegative than the metal and it is assigned an oxidation number of –1.
• Rule: name the metal + hydrideRbH Rubidium hydrideCsH Cesium hydrideLiH Lithium hydride
Systematic Naming of Compounds• Ternary Compounds• compound which is composed of
three or more elements
Ternary Acids or Oxy-Acids
• Dry form• Rule: Hydrogen + Oxy-ion in –ATE form
H2CO3 Hydrogen carbonate
H3PO4 Hydrogen phosphate
• Rule: Hydrogen + Oxy-ion in –ITE formH2SO3 Hydrogen sulfite
H3PO3 Hydrogen phosphite
Ternary Acids or Oxy-Acids
• Aqueous form• The negative ion is in the form of suffix
–ATE• Rule: name the root of the middle
element + IC plus the word acidH2CO3(aq) Carbonic acid
• The negative ion is in the form of suffix –ITE
• Rule: name the root of the middle element + OUS plus the word acid
H2SO3(aq) Sulfurous acid
Ternary Salts
• Salts of the oxy-acids (Metal + Oxy-ion)
• Metals with fixed oxidation number.
• Rule: name the metal or (+) ion + name of the negative (-) ion
NaNO3 Sodium nitrate
NaNO2 Sodium nitrite
Ternary Salts
• Salts of the oxy-acids (Metal + Oxy-ion) • Metals with fixed oxidation number.
• Metals with variable oxidation numbers• Rule: name the metal or positive ion
(Roman numeral) + name of the negative ion.
FeCO3 Iron (II) carbonate