Download Hints for Names and Formulas (Ch. 4 in Zumdahl Chemistry)

Hints for Names and Formulas (Ch. 4 in Zumdahl Chemistry)
COVALENT MOLECULES AND COMPOUNDS
(1) in this course, molecules are usually defined as two or more nonmetallic atoms bonded covalently
(2) molecules are finite groupings of nonmetallic atoms that may or may not be different elements
● only 10 elements exist as molecules when free in nature: H2, N2, O2, F2, Cl2, Br2, I2, At2, P4, S8
● these 10 elements may have different subscripts when in combination with other elements
◘ examples: H2O, CO, CCl4, CaBr2 (ionic), Na2O (ionic)
◘ reaction: 4 Na(s) + O2 (g) → 2 Na2O(s)
(3) molecules can have either single, double or triple covalent bonds
● examples: H-H, O=O, N≡N, H-O-H, CH4 (4 single bonds)
(4) only true covalent molecules can be built with the molecular model kits with gray bonds
(5) only covalent compounds (with all nonmetals) use prefix-type nomenclature
● examples: CO2 (carbon dioxide), N2O5 (dinitrogen pentoxide), CCl4 (carbon tetrachloride)
(6) covalent compound formulas usually list the more positive oxidation state first and more negative last
● examples: CO2 (C+4 and O-2), N2O5 (N+5 and O-2), CCl4 (carbon tetrachloride)
● exceptions: NH3 (N-3 and H+1), PH3 (P-3 and H+1), and a few others
(7) all polyatomic ions have atoms that are bonded covalently, but total charge does not equal zero
(8) most organic molecules are named according to systematic IUPAC nomenclature rules
● IUPAC stands for the International Union of Pure and Applied Chemistry committee
(9) most covalent inorganic molecules are gases (sometimes liquids) at room temperature (R.T.)
IONIC COMPOUNDS
(1) ionic compounds are never called molecules and have covalent bonds only in their polyatomic ions
(2) ionic compounds are generally classified as salts, acids, or bases
(3) ionic compounds are orderly, infinite arrangements of positive and negative ions
(4) ionic compounds are built with foam balls and toothpicks, not the molecular model kits
(5) The positive ion (cation) is written first, and is usually a metallic ion and uses the name of the metal
● transition metals, tin and lead are known to have more than one ionic charge and must be
shown in the name as a Roman numeral in parentheses
◘ examples: CuCl is copper(I) chloride and CuCl2 is copper(II) chloride
(6) The negative ion (anion) is written last, and is either a nonmetallic ion or a negative polyatomic ion
● for a negative, monoatomic ion, the name of the nonmetallic element ends in "-ide"
● for polyatomic anions, parentheses are needed if there are two or more of them present
◘ examples: Co(OH) 3 is cobalt(III) hydroxide and Al2(SO3) 3 is aluminum sulfite
(7) The sum of the positive and negative charges must total zero for any ionic compound formula
● this fact enables you to predict the subscripts of the ionic formula
◘ in aluminum sulfate Al3+ ion combines with sulfate SO42- ion to form Al2(SO4) 3
because two times Al3+ = +6 and three times SO42- = -6, and +6 and -6 = 0
(8) Most ionic compounds are solids at R.T., have high melting points (M.P.), and may be soluble in water
(9) When dissolved in water, the physical change can be shown in a dissociation equation:
[notice that both atoms and charges balance]
Al2 (SO4) 3 (s) → 2 Al3+ (aq) + 3 SO42- (aq)
OTHER BONDING ARRANGEMENTS
(1) covalently-bonded atoms in an orderly, infinite arrangement are called network solids
● examples: graphite, (pure C), diamond (pure C), and quartz (SiO2 network)
(2) metals have unique orderly, solid structure called metallic bonding with mobile electrons around cation
● examples: gold, silver, sodium, calcium, etc.
TECHNICAL NOTES
(1) ion charges are always oxidation states, but oxidation states are not always ion charges!
(2) for ionic charges the number is followed by the sign, S2-; otherwise the sign is followed by the number, S+6
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H 2O
water
dihydrogen oxide
H 2O 2
CHEMICAL COMPOUND SYSTEMATIC NOMENCLATURE
hydrogen peroxide
dihydrogen dioxide
NaCl
metal present?
table salt
sodium chloride
no
P4O10
yes
ionic cpd;
infinite crystal model
tetraphosphorus decoxide
Al2O3
metal have more than
one cation charge?
use prefix name
bauxite
aluminum oxide
Ag2S
silver tarnish
silver sulfide
N 2O
nonmetal-nonmetal;
covalent molecule;
ball & stick model
laughing gas
dinitrogen monoxide
no
use the element name
for the cation
yes
use (Roman numeral)
after positive element
name
CuBr
copper (I) bromide)
cuprous chloride
CuBr2
copper (II) bromide)
Prefix Names (nonmetals-nonmetals bonded covalently)
(1)
(2)
(3)
(4)
First element in the formula is named first using the element name.
Second element is named as if it were a monatomic anion, i.e., CO2
Prefixes are used to denote the numbers of atoms present:
Exceptions:
(a) the prefix “mono-” is never used for naming the first element.
(b) drop the final vowel of the prefix if the element begins with a vowel.
monoditritetrapenta-
(1)
(2)
(3)
(4)
(5)
hexaheptaoctanonadeca-
(6)
(7)
(8)
(9)
(10)
Element Names (metals bonded ionically to nonmetal or polyatomic anions)
(1)
(2)
(3)
(4)
(5)
The cation is always named first and the anion named second.
A monatomic cation takes its name from the name of the element.
A monatomic anion is named by taking the root of the element name and adding “-ide”.
Polyatomic anion names must be memorized although there are several nomenclature shortcuts.
Polyatomic anions must be surrounded by parentheses only when more than one is present in compound.
Roman Numeral Names (metals having more than one positive charge)
(1)
(2)
(3)
(4)
Some metals, especially transition metals, have more than one possible charge.
Figure out the charge on each metal ion by adding up all the negative charges; total charges must equal zero.
Place the Roman numeral equivalent of the positive charge in parentheses right after the name of the metal.
You also need to know the older naming system which adds to a root name the suffixes “ic” and “-ous” for the
higher and lower charges, respectively, on elements with only two charges. i.e., “ferrous” for iron(II) and
“ferric” for iron(III).
(5) Roman numerals are NEVER written in formulas, only in names of compounds!
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