Chemical Formulas And Chemical Compounds
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2CHAPTER 7, CHEMICAL FORMULAS AND CHEMICAL COMPOUNDS
Binary acids are acids that consist of two elements, usually hydrogen and one of
the halogens.
Section 1, Chemical Names and Formulas
FORMULAS OF IONIC COMPOUNDS
Oxyacids are acids that contain hydrogen, oxygen, and a third element (usually a
nonmetal).
Subscript 3 = 3 of
Al
(SO
)
everything inside
2
4
3
Many polyatomic ions are produced by the loss of hydrogen ions from oxyacids.
parentheses (total of 3
Subscript 2 =
sulfur atoms and 12
Some examples include: sulfate from sulfuric acid, nitrate from nitric acid, and
Subscript 4 = 4 oxygen
oxygen atoms)
2 aluminum
atoms
atoms in sulfate ion
phosphate from phosphoric acid.
Aluminum Sulfate
!
An ionic compound composed of a cation and the anion from an acid is often
referred to as a salt. For example: NaCl contains the anion from HCl.
A monatomic ion is an ion formed from a single atom.
Monatomic cations are identified simply by the element’s name.
Section 2, Oxidation Numbers
Monatomic anions are identified by dropping the ending of the element’s name and
In order to indicate the general distribution of electrons among the bonded atoms in
adding –ide.
a molecular compound of a polyatomic ion, oxidation numbers, also known as
oxidation states, are assigned to the atoms composing the compound or ion.
A binary compound is a compound composed of two elements.
Assigning Oxidation Numbers
The nomenclature, or naming system, of binary ionic compounds involves
1.
Atoms in a pure element have an oxidation number of zero.
combining the names of the compound’s positive and negative ions. The name of
2.
The more-electronegative element in a binary molecular compound is
the cation is given first.
assigned the number equal to the negative charge it would have as an
anion.
The Stock system of nomenclature is used for elements that form tow or more
3.
Fluorine has an oxidation number of -1 in all of its compounds because it
cations with different charges. This system used a Roman numeral to indicate an
is the most electronegative element.
2+
ion’s charge. For example, Fe
is iron(II).
4.
Oxygen has an oxidation number of -2 in almost all compounds.
Exceptions: peroxides (such as H
O
) where oxidation number is -1 &
Oxyanions are polyatomic ions that contain oxygen.
2
2
compounds with F (such as OF
) where oxidation number is +2.
2
5.
Hydrogen has an oxidation number of +1 in all compounds containing
FORMULAS OF BINARY MOLECULAR COMPOUNDS
elements that are more electronegative than it; it has an oxidation number
Old System for Naming…is based on the use of prefixes.
of -1 in compounds with metals.
Rules
6.
The algebraic sum of the oxidation numbers of all atoms in a neutral
1.
The element that has the smaller group number is usually first. If both
compound is zero.
elements are in the same group, the element whose period number is
7.
The algebraic sum of the oxidation numbers of all atoms in a polyatomic
greater is given first. The element is given a prefix only if it contributes
ion is equal to the charge on the ion.
more than one atom to a molecule of the compound.
8.
Although rules 1 through 7 apply to covalently bonded atoms, oxidation
2.
The second element is named by combining
number can also be assigned to atoms in ionic compounds.
a.
a prefix indicating the number of atoms contributed by the
9.
A monatomic ion has an oxidation number equal to the charge of the ion.
element,
b.
the root of the name of the element, and
Listing of oxidation numbers: Appendix Table A-15.
c.
the ending –ide.
With few exceptions, the ending –ide indicates that a compound contains
FORMULAS OF BINARY MOLECULAR COMPOUNDS
only two elements.
New Stock System for Naming…is based on oxidation numbers.
3.
The o or a at the end of a prefix is usually dropped when the word
For example, PCl
! Prefix System = phosphorous trichloride | Stock System =
following the prefix begins with another vowel.
3
phosphorous(III) chloride
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