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Molecules
Most elements found in nature are not found as isolated atoms. Noble gases are common exceptions.
Most natural materials are composed of either: molecules Ions
Molecules and ions are both formed from atoms.
Molecules
Molecule: A group of atoms combined in definite
proportions and held together by strong attractive forces called covalent chemical bondsCovalent bonds are formed when two
atoms share two or more electrons
The smallest representative particle of a molecular compound
Molecular Compounds
Molecular compounds composed of molecules that contain more than one
type of atom
Examples: Water (H2O) Ethyl alcohol (C2H6O) Carbon dioxide (CO2) Ozone (O3)
Most molecular substances are composed of non-metals only.
Chemical Formulas
Chemical Formula notation that describes the types and
relative numbers of atoms in a pure substance
Chemical formulas always contain: elemental symbols subscripts
show the relative number of each type of atom
Chemical Formulas
Molecular Formulas chemical formulas that tell the actual
number of each type of atom in a molecule
provide the greatest information about a compound
Acetic Acid C2H4O2
Glucose C6H12O6
Chemical Formulas
Empirical Formula chemical formula that tells the smallest
whole number ratio of each type of atom in a molecule
NO2 vs. N2O4
HO vs. H2O2
CH2 vs. C3H6
Ions and Ionic Compounds
Some compounds are composed of ions instead of molecules. “Salt” (NaCl)
contains Na+ and Cl- ions
Tums (CaCO3)Contains Ca2+ and CO3
2- ions
Milk of Magnesia [Mg(OH)2]Contains Mg2+ and OH-
Ions and Ionic Compounds
Ions can be either monoatomic polyatomic
Ions form when atoms (or groups of atoms) gain or lose electrons
Monoatomic ion: a charged substance containing a single
atom that has gained or lost electrons
Predicting Ionic Charge
Many atoms gain or lose electrons in such a way that they end up with the same number of electrons as the nearest (closest in atomic number) noble gas. “octet” rule
Ca (20p, 20e-) Ca2+ (20p, 18e-) [Ar: 18p,18e-]
O (8p, 8e-) O2- (8p, 10e-) [Ne: 10p, 10e-]
Predicting Ionic Charge
Using the octet rule you can easily determine the charge on most of the monoatomic ions formed by the main group elements.
Main group metal cations:Charge = group number
Main group nonmetal anions:Charge = group # - 8
(or simply count the number of “spaces” away from the nearest noble gas and add a negative sign)
Ions and Ionic Compounds
In general:Metal atoms lose e- and form cations.Nonmetal atoms gain e- and form anions.
Common monoatomic ions
Zn2+
Ag+
P3-
Ions and Ionic Compounds
Mai
n gr
oup
Fe2+
Fe3+
Cu+
Cu2+
Mn2+
Mn3+
Co2+
Co3+
Bi3+
Bi5+
Cr2+
Cr3+
Sn2+
Sn4+
Pb2+
Pb4+
Many transition metals and a few main group elements form more than one ion.
Main group
Ions and Ionic Compounds
Polyatomic ion: an electrically charged group of two or
more atoms that are held together by covalent bondsPolyatomic ions cannot be broken into
smaller pieces
Examples:NO3
-
SO42-
HCO3-
PO43-
O
3-
P O
O
O
Polyatomic Ions Some common polyatomic ions:
Ammonium NH4+
Hydroxide OH-
Cyanide CN-
Nitrate NO3-
Acetate C2H3O2-
Sulfate SO42-
Bisulfate (Hydrogen sulfate) HSO4-
Carbonate CO32-
Bicarbonate (Hydrogen carbonate) HCO3-
Phosphate PO43-
Common Ions
You are responsible for naming and writing formulas for compounds containing the ions shown in the Ion Chart given to you at the start of the semester.
You should be able to write the names and formulas for binary molecular compounds and the common acids shown in this set of notes.
You should also know the formulas and names of compounds that you use in the laboratory.
Ionic Compounds
Ionic Compound a compound that contains both cations
(+ charge) and anions (- charge)
Ionic compounds generally contain a metal and one or more nonmetals.
Molecular compounds generally contain nonmetals only.
Structures & Formulas of Ionic Compounds
The ions in an ionic compound are arranged in a 3-D structure.
There are no discrete molecules of an ionic compound. Ionic compounds are
represented using empirical formulas
Formulas of Ionic Compounds
Ionic compounds must be electrically neutral. Total positive charge = total negative
charge
Na+ + Cl- NaCl (1 pos, 1 neg)
Na++Na++ Cl-
Ca2+ + Cl- CaCl (2 pos, 1 neg)
Ca2+ + 2Cl- CaCl2 (2 pos, 2 neg)
Ca2+Cl-
Ca2+Cl-
Cl-
Formulas of Ionic Compounds
To write the empirical formula for an ionic compound: Determine the charge on each ion. Combine the ions in a ratio that gives
electrically neutral compoundIf charges on the ions are equal in
magnitude (but opposite in sign), then combine the ions in a 1:1 ratio.
Formulas of Ionic Compounds
If charges on the ions are different, then the charge of one ion becomes the subscript of the other ion.
Mg+2 Cl -1 Mg1Cl2 MgCl2
If the subscripts are not the lowest whole number ratio, divide them by the greatest common factor.
Formulas of Ionic Compounds
Al3+ O 2-
Example: Write the correct formula for a compound containing Al3+ and O2- ions
Al2O3
O2- O2- O2-
Al3+ Al3+
Formulas of Ionic Compounds
Al3+ SO42-
Example: Write the empirical formula for the compound formed from Al3+ and SO4
2- ions.
Al2(SO4)3
SO4 2-
Al3+ Al3+
SO4 2-SO4 2-
Formulas of Ionic Compounds
Example: What are the empirical formulas for the compounds formed from:
Ca2+ and N3-
Sn4+ and SO42-
Remember to use ( ) around polyatomic ions if you need more than one of them.
Formulas of Ionic Compounds
Names & Formulas of Ionic Compounds
Ionic compounds are named using the names of the ions that compose them. You must know the names and charges
of all ions, including the polyatomic ions. Ion chart hand-outTrends discussed during lecture
General format for naming ionic compounds:Cation name followed by anion name
Naming Cations
Cations formed from metal ions have the same name as the metal.
K+ potassium ionCa2+ calcium ionAl3+ aluminum ion
Naming Cations
Many transition metals and a few main group metals can form more than one cation (i.e. two or more charges) the charge of the specific cation is given by
Roman numeral in parentheses after the name of the metal
Fe2+ iron (II) ionFe3+ iron (III) ionCu+ copper (I) ionCu2+ copper (II) ion
Naming Anions
Monoatomic anions
drop the ending of the element’s name add “ide”
N nitrogen N3- nitride
O oxygen O2- oxide
Naming Anions
Some simple polyatomic anions also use the “ide” ending
OH- hydroxideCN- cyanideO2
2- peroxide
Naming Oxyanions
Oxyanions (polyatomic anions containing oxygen) have names ending in: “ate” most common oxyanion
of the element “ite” same charge, 1 less O
NO3- nitrate SO4
2- sulfate
NO2- nitrite SO3
2- sulfite
Oxyanions (cont.)
Prefixes are added if more than 2 oxyanions exist:
“per” 1 more O than the “ate” oxyanion “hypo” 1 less O than the “ite” oxyanion
ClO4- perchlorate
ClO3- chlorate
ClO2- chlorite
ClO- hypochlorite
Oxyanions
To learn & remember the names and formulas of the oxyanions:
learn the name and formula for the “ate” oxyanion
apply the rules discussed previously
Oxyanions
The names & formulas of the common oxyanions can be learned using trends within the same group of elements:
Halogens:The “ate” anion has 3 oxygens and a 1-
charge
ClO3- = chlorate ion
BrO3- = bromate ion
Oxyanions
Group 6 (S, Se, Te): The “ate” anion has 4 oxygens and a 2- charge SO4
2- = sulfate SeO4
2- = selenate
Group 5 (N, P, As): The “ate” anion has 4 oxygens and a 3- charge
except for Nitrogen PO4
3- = phosphate NO3
- = nitrate
Oxyanions
Other common oxyanions that you must know:
MnO4- = permanganate ion
CrO42- = chromate ion
Cr2O72- = dichromate ion
Oxyanions
Anions derived by adding H+ to an oxyanion: add “hydrogen” or “dihydrogen” as prefix
to oxyanion name
CO32- carbonate
HCO3- hydrogen carbonate
(also called bicarbonate)
PO43- phosphate
H2 PO4- dihydrogen phosphate
Ionic Compounds
Ionic compounds are named by: Cation name followed by anion name
NaCl
CaBr2
NaClO
Cu(NO3)2
sodium chloride
calcium bromide
sodium hypochlorite
copper (II) nitrate
Writing Formulas from Names
To write the correct empirical formula from the name of an ionic compound: Identify the symbol and charge for each
ion. Determine the correct number of each ion
needed to balance the charges.
Writing Formulas from Names
Example: Write the empirical formula for ammonium sulfate
(NH4)2SO4
ammonium
sulfate
NH4+
SO42-
Writing Formulas from Names
sodium bicarbonate barium nitrate sodium bromate iron(III) carbonate sodium hydrogen phosphate potassium dichromate tin (IV) oxide
Example: Write the formulas for these ionic compounds
Names & Formulas of Acids
Acid: a substance whose molecules form H+
ions when dissolved in water
HCl (aq) HCN (g) HClO3 (aq)
Name of acid depends on the type of acid, its physical state, and the name of the anion.
Names & Formulas of Acids
Three naming systems for acids:
Acids containing oxygen
Acids without oxygenaqueous solutionsgases
Naming Acids
To name an acid: Does it have oxygen?
YesWrite name of anionChange “ate” to “ic acid”
Example: HClO4 = perchloric acid
Change “ite” to “ous acid”Example:
HClO2 = chlorous acid
Naming Acids
To name an acid: If no oxygen, is it (aq)?
YesStart with hydroAdd the name of anionChange “ide” to “ic acid”
Example:HCl (aq) = hydrochloric acid
Naming Acids
To name an acid: If no oxygen, is it (g)?
YesStart with hydrogenAdd the name of the anion
Example:HCN (g) = hydrogen cyanide
Naming Acids
You must know the names and formulas for the following acids for the exam:
HCl (aq) hydrochloric acid HBr (aq) hydrobromic acid HI (aq) hydroiodic acid HNO3 nitric acid HClO4 perchloric acid HClO3 chloric acid H2SO4 sulfuric acid
Naming Acids
You must know the names and formulas for the following acids for the exam:
HF (aq) hydrofluoric acid H2S (g) hydrogen sulfide HCN (g) hydrogen cyanide HC2H3O2 acetic acid H2CO3 carbonic acid H3PO4 phosphoric acid
Writing Formulas for Acids
Which category of acid is it? Oxyanion based Not oxyanion based, (aq) Not oxyanion based, (g)
Write the formula for the anion (including charge).
Add enough H ions to make a neutral compound.
Example
Example: Write the formula for perchloric acid.
Category: oxyanion containing acid
Anion: perchloric acid
Formula: HClO4
perchlorateClO4
-
Binary Molecular Compounds
Binary molecular compound: compound composed of molecules with
two different types of atoms
Remember: Many molecular compounds are composed strictly of non-metals.
SO2 N2O4
H2O PCl5
P4O10 CO
Binary Molecular Compounds
The names of binary molecular compounds give both the type and number of each type of atom present.
The general pattern for naming binary molecular compounds is:
______element name ______ element name with ide ending______element name ______ element name with ide ending
Binary Molecular Compounds
The first element is named using the name of the element.
The second element is named using the “ide” ending.
Greek prefixes are used to indicate the number of each type of element present.
______element name ______ element name with ide ending______element name ______ element name with ide ending
Greek Prefixes
Prefix Meaningmono 1di 2tri 3tetra 4penta 5hexa 6hepta 7octa 8nona 9deca 10
You must know these!!You must know these!!
PP44SS1010 = =
tetraphosphorus decasulfide
Binary Molecular Compounds
Special conventions for using Greek prefixes: Mono is never used with the first element
The “a” or “o” in the prefix is dropped if the name of the element begins with a vowel.
CO: carbon monooxide carbon monoxide
Binary Molecular Compounds
Example: Write the formulas for the following compounds.
tetraphosphorus decoxide
sulfur trioxide
disulfur dichloride
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