Chapter 7 (nomenclature) class notes CHEM

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Transcript Chapter 7 (nomenclature) class notes CHEM

Chemical Formulas and
Chemical Compounds
Chapter 7
Pages 219 – 249
Chemical Formula
Significance
MOLECULAR COMPOUNDS: formula reveals the
number of atoms of each element contained in a
single molecule.
EXAMPLE: octane C8H18
How many atoms of carbon exist in this molecule? Of
hydrogen?
Chemical Formula
Significance
Chemical Formula
Significance
IONIC COMPOUNDS: consist of a lattice of positive
and negative ions held together by electrostatic
attraction. These formulas represent one unit – the
simplest ratio of the compound’s cations (+) and
anions (-).
EXAMPLE: aluminum sulfate Al2(SO4)3
Given that aluminum metal always forms 3+ cations
and the sulfate polyatomic ion always forms 2anions, explain the above chemical formula for the
compound.
Chemical Formula
Significance
MONATOMIC IONS: ions formed from a single atom.
For examples, refer to table 1 on page 221. Memorize
these ions and the charges they form in compounds.
NOMENCLATURE: a method of naming items within a
system of various entries.
NAMING MONATOMIC CATIONS (+): identify by the
element’s name.
EXAMPLE: K+ is called ___________? Mg2+ is called
________?
Chemical Formula
Significance
NAMING MONATOMIC ANIONS (-): 1) the ending of
the element’s name is dropped. 2) a suffix of –IDE is
added to the root name.
Please refer to your textbook page 221 table 1.
“digital insert” – NAMING MONATOMIC IONS
EXAMPLE: when the element fluorine becomes an
anion (a negatively charged ion) it is no longer
fluorINE but is now called fluorIDE.
Chemical Formula
Significance
BINARY COMPOUNDS: are compounds composed of two elements.
For ionic compounds, the charges on the ions in the compound will
always neutralize or CANCEL EACH OTHER OUT.
EXAMPLE: magnesium bromide – note that magnesium is an alkaline
earth metal while bromine is a nonmetal (specifically a halogen.
What charge to all halogens take when they form ions?) – this should
tell you that this is an ionic compound. Since Mg has a 2+ charge and
Br has a 1- charge, what will the chemical formula be for this ionic
compound?
When naming compounds, the cation (+) always is written first,
followed by the anion (-).
Chemical Formula
Significance
PRACTICE: What is the formula for the following
binary ionic compounds?
Potassium and iodine
Sodium and sulfur
Aluminum and nitrogen
Chemical Formula
Significance
ANSWERS
KI
(because potassium has a +1 charge while iodine has a -1 charge)
Na2S
(because sulfur makes a -2 anion when forming an ionic bond while
sodium carries a +1 charge)
AlN
(because Al always carries a +3 charge as an ion while N carries a -3
charge as an Anion)
Chemical Formula
Significance
TRANSITION METALS NOMENCLATURE: to name
these, roman numerals are used to indicate the
charge on the cation (+).
EXAMPLE: CuCl2 Copper (II) chloride. Since this bond
consists of a METAL and a NONMETAL, the charges
on each atom cancel. What is the charge on the
copper atom? On the chlorine atom?
PRACTICE: What is the name and formula for a
compound formed from the ions Cr3+ and F-?
Chemical Formula
Significance
ANSWER
NAME: Chromium (III) Fluoride
FORMULA: CrF3
QUESTIONS?
Chemical Formula
Significance
SOME COMMON POLYATOMIC IONS:
Hydroxide, OHNitrate, NO3Carbonate, CO32Sulfate, SO42Phosphate, PO43-
Chemical Formula
Significance
NAMING BINARY MOLECULAR COMPOUNDS: or covalently bonded
compounds, prefixes are used to show how many atoms of an
element are participating in the bond.
Refer to table 3 on page 228 and MEMORIZE the prefixes that are
associated with the number of atoms in a compound.
The o or a at the end of a prefix is dropped when the word following
the prefix begins with another vowel.
EXAMPLE: monoxide or pentoxide NOT mono-oxide or penta-oxide.
P4O10 Use table 3 to determine the name for this compound.
“digital insert” - Naming binary compounds using numerical
prefixes
Chemical Formula
Significance
MEMORIZE: Table 5 page 230
Binary acids and oxyacids: HF = hydrofluoric acid; HCl = hydrochloric
acid – note that these acids have only hydrogen and another atom
bonded to them.
H2PO4 = phosphoric acid; HNO2 = nitrous acid; HNO3 = nitric acid –
note that the suffix –ous indicates there are only 2 atoms of oxygen
while –ic indicates there are 3.
H2SO3 = sulfurous acid; H2SO4 = sulfuric acid – again note that –ous
indicates there are 3 atoms of oxygen while –ic suffix indicates there
are 4 atoms of oxygen.
Rules of thumb for oxyacids – the larger numbers of oxygen have the
“-ic” suffix while the smaller numbers of oxygen have the “-ous”
suffix.
Chemical Formula
Significance
RULES OF THUMB FOR NAMING COMPOUNDS:
If the compound is ionic (consists of a cation and an anion), use
the name of the first element (+) and then the name of the
second element (-) but drop the ending and add –ide.
If the compound contains a transition metal, use a roman
numeral to indicate the charge on the cation (the metal) and
write the name of the anion (the nonmetal or polyatomic ion),
drop the ending of the anion and add – ide.
If the compound is covalent (two nonmetals) use prefixes to
indicate the number of atoms of each – the cation and the anion.
Oxidation Numbers
Charges on ions composing ionic compounds reflect
electron distribution of compound.
Oxidation numbers indicate the general electron
distribution in a compound.
“digital insert” – “Rules for assigning oxidation
numbers”
Nomenclature Quiz
In a molecule of octane, C8H18, how many atoms of carbon are
present? How many atoms of hydrogen are present? How
many atoms, total, make up a molecule of octane?
What is the name of the compound KI? CuCl2?
What is the chemical formula for dinitrogen pentoxide?
Tetraphosphorus decoxide?
What is the name of the compound HNO3? HNO2? HI?
Assign oxidation numbers for each atom in the following
compounds: HCl, HClO3, N2O5 and CF4.
Answers
8 ; 18 ; 26
Potassium Iodide ; Copper (II) Chloride
N2O5 ; P4O10
Nitric Acid ; Nitrous Acid ; Hydroiodic acid
H +1 ; Cl -1
H +1 ; Cl +5 ; O -2
N +5 ; O -2
C +4 ; F -1