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Chemical Names and Formulas
The total number of natural and synthetic chemical compounds runs in the millions
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For example, everybody recognizes dihydrogen monoxide by its popular name,
water
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For a molecular
compound, the chemical formula reveals the number of atoms of
element contained in a single molecule of the compound
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Subscript indicates that there are 18 hydrogen atoms in a
molecule of octane
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The chemical formula for an ionic compound represents one formula unit—the simplest ration of the
compound’s positive ions (cations) and its negative ions (anions)
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Subscript 4 refers to 4 oxygen
polyatomic sulfate anions, is:
Al2(SO4)3

atoms in sulfate ion
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Monatomic Ions
By gaining or losing electrons, many main-group elements form ions with noble-gas configurations
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Group 2 metals lose two electrons to give 2+ cations,
such as Mg 2+
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The nonmetals of Groups 15, 16, and 17
gain electrons form anions
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Rather than gain or lose electrons, atoms carbon and silicon
form covalent bonds in which they share electrons with other atoms
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Elements from the d-block form 2+, 3+, or, in a few cases, 1+ or 4+ cations
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For example, copper form s 1+ and 2+ cations as well as 3+ cations
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Naming Monatomic Ions
Monatomic cations are identified simply by the element’s name
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First, the
ending of the element’s name is dropped
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The numerals of the ions in the tables are part

Examples of Anions
Element
F
Flourine
N
Nitrogen

Anion
FFluoride anion
N-3
Nitride anion

of the Stock system of naming chemical ions and elements
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In a binary ionic compound, the total of
positive charges and negative charges must be equal
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EX: Magnesium and Bromine combine to form the ionic compound magnesium bromide
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Bromine forms the Br- anion when combined with a metal
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The compound’s formula must therefore indicate
one Mg2+ cation and two Br
anions
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Ions combined: Mg2+, Br-, Br-

Chemical formula: MgBr2

Note that the 2 in Br is written as a subscript
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This is usually the
case when writing formulas for binary ionic compounds
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” Crossing over is a method of balancing the charges between ions in an ionic compound
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1
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Write the cation first
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Cross over the charges by using the absolute value of each ion’s charge as the subscript for the other ion
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Check the subscripts and divide them by their largest common factor to give the smallest possible whole-number
ratio of ions
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Multiplying the charge by the subscript shows that the charge on two Al cations (2 x 3+ = 6+) equals the charge
of three O2- anion (3 x 2- + 6+)
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The correct formula is
therefore written as follows
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The name of the cation is given first, followed by the name of the anion
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The Stock System of Nomenclature
Some elements, such as iron, form two or more cations with different charges
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This system sues a Roman numeral to indicate an ion’s charge
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EX: Fe

iron (II)

Names of metals that commonly form only one cation do not include a Roman numeral
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Compounds Containing Polyatomic Ions
Most common polyatomic ions are negatively charged and oxyanions—polyatomic ions that contain oxygen
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The name of the ion with the greater
number of oxygen atoms ends in –ate
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In a
case where an element can form more than two types of oxyanions, the one that has one fewer oxygen atom than the –ite
anion has is given the prefix hypo-
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Compounds containing polyatomic ions are named in the same manner as binary ionic compounds
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Naming Binary Molecular Compounds
Unlike ionic compounds, molecular compounds are composed of
individual covalently bonded units, or molecules
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The newer system is
the Stock system for naming molecular compounds, which requires and
understanding of oxidation numbers
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For example, the
molecular compound CCl is named carbon tetrachloride
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The two oxides of carbon, CO and CO , are named carbon
monoxide and carbon dioxide, respectively
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1
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If both elements are in the same group, the element whose period number is greater is given first
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2
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With few exceptions, the ending –
ide indicates that a compound contains only two elements
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The o or at the end of a prefix is usually dropped when the word following the prefix begins with another
vowel
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In general, the order of nonmetals in binary compound names and formulas is C, P, N, H, S, I, Br, Cl, O, and F
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Instead, each atom is joined to all its neighbors’
distinct units in these compounds, just as there are no such units in ionic compounds
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SiC = silicon carbide
SiO = silicon dioxide
Si N = tirsilicon tetranitride
Acids and Salts
An acid is a distinct type of molecular compound
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Binary acids are acids that consists of two elements, usually hydrogen and one of the halogens—

fluorine, chlorine, bromine, iodine
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Acids were first recognized as a specific class of compounds based on their properties in solutions of water
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Many polyatomic ions are produced by the loss of hydrogen ions from oxyacids
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Table salt, NaCl,
contains the anion from hydrochloric acid
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Some
slats contain anions in which one or more hydrogen atoms from the acid are retained
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The best known such anion comes from carbonic acid,
H2CO3
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