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Chemical Nomenclature and Chemical Formulas
Chemistry is involved with various and diverse interactions of matter either around us or simply inside the laboratory. These are described using the language of chemistry which consists of symbols, formulas and equations.
Symbols are used as shorthand abbreviations for elements composed of a single capital letter or a capital letter and one or two small letters like H, O, Cl, Na, or Unq.
Formulas are combinations of symbols such as CO2 for carbon dioxide, C6H22O11for table sugar and HCl for hydrochloric acid.
Chemical reactions are composed of elements and compounds which are described through chemical equations using symbols and formulas.
Chemical symbols are shorthand abbreviations for elements composed of a single capital letter or a capital letter and one or two small letters.
Chemical formula indicates the relative number of atoms of each element in a substance. It consists of symbols of elements and subscripts which give the number of atoms of each element.
- The formula of water is H2O
There are 2 atoms of Hydrogen and 1 atom of oxygen
- The formula of glucose is C6H12O6
There are 6 atoms of Carbon, 12 atoms of Hydrogen and 6 atoms of Oxygen.
In writing formulas, the total positive charges plus the total negative charges must equal to zero since the compound is electrically neutral.
Rules in writing formulas of compounds
There are basic rules in writing formulas of compounds. These are:
- Write first the symbol of the positive ion followed by the symbol of the negative ion or radical. A radical or polyatomic ion is a group of atoms which acts as a single atom.
- Criss-cross: the valence of the positive ion becomes the subscript of the negative ion, while the valence of the negative ion becomes the subscript of the positive ion. (You have to disregard the sign) Example: Al+3 O-2 = Al2O3
- If the valence is numerically equal, there is no need to criss -cross since the sum of the valence is zero. Example: Ca+2O-2 = CaO
- Do not write the subscript if it is only 1.
- If the subscript of the radical is greater than 1, the radical is enclosed with a parenthesis. Example: Mg-2PO-3 = Mg3 (PO2)2
- Subscripts should be reduced to the lowest ratio. Example: Sn+4 O-2 = Sn2 O4 = SnO2
How Are Compounds Named
There are several types of compounds. These are the acids, bases, salts, and oxides. This lesson will show you how to name each compound correctly.
These are compounds of weakly bonded H atoms. In solution, they release ions. A given nonmetal may form a series of acids.
HBrO3 - Bromic acid
HlO3 - Iodic acid
HClO3 - Chloric acid
HBO3 - Boric acid
HMnO3 - Manganic acid
H2SO4 - Sulfuric acid
H3PO4 - Phosphoric acid
H3AsO4 - Arsenic acid
- Note that all acids above have names ending in ‘ic’ attached to the stem of the name of the nonmetal. The number of oxygen atoms in common acid is either 3 (column 1) or 4 (column 2). You have to remember this:
To name a series of acids formed by a given nonmetal, consider the following:
HClO4 perchloric acid
HCIO3 chloric acid
HCLO2 chlorous acid
HCIO hypochlorous acid
HCI hypochloric acid
The system adopted is as follows:
- The suffix ‘ic’ denotes the common acid (HCIO3).
- The suffix ‘ous’ denotes an acid containing one less oxygen atom than the common acid (HCIO2).
- The prefix ‘hypo’ with the suffix ‘ous’ denotes an acid with two less oxygen atoms than the common acid (HCIO).
- The prefix ‘per’ with the suffix ‘ic’ denotes an acid containing one more oxygen atom than the common acid (HClO4).
- The prefix ‘hydro’ with the suffix ‘ic’ denotes an acid with no oxygen (HCl).
Answer the following:
1. Name the following acids:
2. Write the chemical formula of the following:
a. Hydrobromic acid d. Hypoiodous acid
b. Nitrous acid e. Bromous acid
c. Periodic acid
- Note: (c) is read as per-iod-ic acid.
Names of 10 Acids
- 10 Common Acids and Chemical Structures
Here is a list of ten common acids with chemical structures.
These are the compounds identified by the presence of the hydroxide group (OH). Name of the metallic portion first followed by the word hydroxide.
NaOH - Sodium Hydroxide
Fe(OH)2 - Iron(II) Hydroxide or Ferrous Hydroxide
Fe(OH)3 - Iron(III) Hydroxide or Ferric Hydroxide
Names of 10 Bases
- Names of 10 Bases With Chemical Structures and Formulas
Here is a list of ten common bases with chemical structures.
The strengths and weaknesses of acids and bases
Salts are formed when metallic atoms replace the weakly bonded hydrogen atoms of an acid. They are named after the acid from which they are formed. The name of the metal comes first, followed by the name of the nonmetallic group. The ending ‘ic’ is changed to ‘ate’ and the ending ‘ous’ to ‘ite’. For salts with no oxygen atom, the prefix ‘hydro’ is dropped and ending ‘ic’ is changed to ‘ide’.
For example, the acid HNO3 (nitric acid) forms the salt KNO3 (potassium nitrate), when the metallic atom K places H atom of the acid. As another example, the acid HNO2 (nitrous acid) forms the salt KNO potassium nitrate). The ending ‘ous’ of the acid is changed to ‘ite’.
HI (hydroiodic acid) forms the salt KI (potassium iodide). Since there is no more hydrogen atom in the salt, the prefix “hydro” of the acid name is dropped. The ending ‘ic’ of the acid is changed to “ide’ in salt.
♦ Consider the following series:
NaClO4 - Sodium Perchlorate
NaClO3 -Sodium Chlorate
NaClO2 - Sodium Chloride
NaClO - Sodium Hypochloride
NaCl - Sodium Chloride
These salts are formed by replacement of the H of the series of acids.
♦ Give the name of each of the following salts:
a. K2SO4 d. Lil
b. Ca3(PO4)2 e. KmnO4
♦ Write the chemical formula of:
a. Sodium Nitrate
b. Magnesium Chloride
c. Calcium Sulfite
d. Sodium Hypobromite
e. Ammonium Periodate
When a metal has a variable oxidation number, its name is followed by the oxidation number written in Roman numeral enclosed in parenthesis. The old method used the stem of the Latin name and the suffixes ‘ous’ and ‘ic’ for the lower and higher states, respectively.
FeCI2 – iron (II) chloride or ferrous chloride
FeCI3 – iron (III) chloride or ferric chloride
Other Metallic Ions with Variable Oxidation Number
tin(II) or stannous
tin(IV) or stannic
mercury(I) or mercurous
mercuric(II) or mercuric
copper(I) or cuprous
copper(II) or cupric
gold(I) or aurous
gold(III) or auric
lead(II) or plumbous
lead(IV) or plumbic
Acids, Bases and Salts
Oxides are compounds of oxygen with metals or nonmetals. Name the metal or the nonmetal first. Then use the prefixes di, tri, tetra or penta before the term oxide to indicate the number of oxygen atoms present. In case where the number of oxygen atom present can determine from oxidation number of the combined metal, the prefix is omitted.
NO2: Nitrogen Dioxide
N2O4: Dinitrogen Tetroxide
P2O5: Phosphorus Pentoxide
PbO: Lead(II) oxide or Plumbous Oxide
PbO2: Lead(IV) oxide or Plumbous Oxide
Questions for Study and Review
I. Name the following compounds by identifying the oxidation number of the metal as you name the compounds listed below:
II. Formula Writing: Write the correct chemical formula of the following:
- Calcium carbonate
- Magnesium hydroxide
- Copper sulfate
- Carbon tetrachloride
- Potassium bromate
- Ammonium hydroxide
- Lead nitrate
- Sulfuric acid
- Nitric acid
- Boric acid