Compounds
description
Transcript of Compounds
Compounds A compound is a pure substance that
contains two or more elements that are chemically bonded to each other
Compounds form when the electrons of two or more elements interact and are composed of either:Molecules
IonsH O
Hwater =
Salt = NaCl Na , Cl
Molecules Molecule:
A group of atoms combined in definite proportions and held together by strong attractive forces called covalent chemical bonds Covalent bonds are formed when
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
Most molecular substances are composed of non-metals only.
Examples:Water (H2O)Ethyl alcohol (C2H6O)Carbon dioxide (CO2)Ammonia (NH3)
Ionic Compounds Ionic compounds are composed of ions
(both cations and anions) and usually contain a metal and one or more nonmetals.
“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-
Ionic Compounds Ionic compounds such as NaCl are formed when
one or more electrons are transferred from one atom to another
the resulting cation and anion are strongly attracted to each other and are held together by an ionic bond resulting from electrostatic forces of attraction
Chemical Formulas The composition of a compound is
generally shown using a chemical formula:A shorthand notation that describes
the types and relative (or exact) numbers of each atom (or ion) present in a pure substance
Chemical formulas always contain:Elemental symbolsSubscripts
Show the relative (or exact) number of each type of atom or ion
Chemical Formulas Molecular Formula
chemical formula that tells the actual number of each type of atom in a molecule
Empirical Formulachemical formula that tells the smallest
whole number ratio of each type of atom in a molecule
Acetic Acid C2H4O2 CH2OAscorbic Acid C6H8O6 C3H4O3Sodium Sulfate Na2SO4
Ionic Compounds The ions present in an ionic compound
can be either:MonoatomicPolyatomic
Monoatomic ion:a charged species containing a
single atom that has gained or lost electrons Al3+
S2-
Predicting Ion Charge – Monoatomic Ions 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 Ion Charge – Monoatomic Ions 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)
Common Monoatomic Ions
In general:Metal atoms and hydrogen lose e- and form cations.Nonmetal atoms gain e- and form anions.
Know These!
Zn2+
Ag+
P3-
Common Monoatomic Ions
Many transition metals and a few main group elements form more than one ion.
Mai
n gr
oup
Fe2+
Fe3+Cu+
Cu2+Mn2+
Mn3+Co2+
Co3+
Bi3+
Bi5+
Cr2+
Cr3+
Sn2+
Sn4+
Pb2+
Pb4+
Main group
Names of Monoatomic Ions - Cations Cations formed by a metal have the
same name as the metal.K+ potassium ionCa2+ calcium ionAl3+ aluminum ion
If a metal forms more than one cation, use Roman numerals in ( ) after the name of the metal to show its charge.
Fe2+ iron (II) ionFe3+ iron (III) ionCu+ copper (I) ionCu2+ copper (II) ion
Names of Monoatomic Ions - Anions Monoatomic anions are named by:
dropping the ending of the element’s name
adding “ide”
N nitrogen O oxygen
N3- O2-nitride oxide
Polyatomic Ions Polyatomic ion:
an electrically charged group of two or more atoms that are held together by covalent bonds Polyatomic ions cannot be broken
into smaller pieces.
Examples: NO3
-
SO42-
HCO3-
PO43-
NHH
HH
Polyatomic Ions You are responsible for knowing the
names and formulas of all ions listed in your syllabus, including the common polyatomic ions: Ammonium NH4
+
Hydroxide OH-
Cyanide CN-
Nitrate NO3-
AcetateC2H3O2
-
Sulfate SO42-
Bisulfate (Hydrogen sulfate) HSO4-
Carbonate CO32-
Bicarbonate (Hydrogen carbonate) HCO3-
Phosphate PO43-
Naming Oxyanions Many of the polyatomic anions are oxyanions.
polyatomic anions containing one or more oxygens attached to a central atom
To name an oxyanion, drop the ending of the central atom name and add: “ate” most common oxyanion
of the element
“ite” 1 less oxygen
NO3- nitrate SO4
2- sulfateNO2
- nitrite SO32- sulfite
CO32- carbonate PO4
3- phosphatePO3
3- phosphite
XOnm-
Oxyanions
Nob
le
gase
s
3A
4A
5A
6A
7A
NO3-
nitrateCO3
2-
carbonateClO3
-
chlorateBrO3
-
bromateIO3
-
iodate
PO43-
phosphateSO4
2-
sulfate
“ate” oxyanions to memorize
Oxyanions The halogens typically form 4 different
oxyanions:
“per” 1 more O than the “ate” oxyanion
“hypo” 1 less O than the “ite” oxyanion
ClO4- perchlorate most oxygens
ClO3- chlorate most common
ClO2- chlorite 1 less O
ClO- hypochlorite fewest oxygens
Oxyanions Anions derived by adding one or two H+
to an oxyanion:
add “hydrogen” or “dihydrogen” as prefix to oxyanion name
CO32- carbonate
HCO3- hydrogen carbonate
(usually called bicarbonate)
PO43- phosphate
H2PO4- dihydrogen phosphate
Writing Formulas for Ionic Compounds Ionic compounds are always
represented using an empirical formula with the cation shown first.
The formula for an ionic compound must be electrically neutral.Total positive charge = total
negative charge
Although ions are present in an ionic compound, the formula does NOT explicitly show the charge of the ions.
NaCl not Na Cl
Writing Formulas for Ionic Compounds Ionic compounds must be electrically
neutral.Total positive charge = total
negative charge
Na+ + Cl- NaCl (1 pos, 1 neg)
Na++Na++ Cl-
Writing Formulas for Ionic CompoundsCa2+ + Cl- CaCl (2 pos, 1 neg)
Ca2+Cl-
Ca2+ + 2Cl- CaCl2 (2 pos, 2 neg)
Ca2+Cl-
Cl-
Writing Formulas for Ionic Compounds To write the empirical formula of an
ionic compound from its name:
1. Identify the formula including charge for each ion.
2. Combine the ions in a ratio that gives an electrically neutral compound.
Writing Formulas for Ionic Compounds If charges on the ions are equal in
magnitude (but opposite in sign), then combine the ions in a 1:1 ratio.
Ca2+ SO42-
sodium bicarbonateNa+ HCO3
-
NaHCO3
calcium sulfateCa2+ SO4
2-
CaSO4
HCO3-Na+
Writing Formulas for Ionic Compounds If charges on the ions are different, then
flip-flop the charges (i.e. the charge of one ion becomes the subscript of the other ion).
Place ( ) around all polyatomic ions IF more than one is needed.
magnesium nitride calcium hydroxide
Ca2+ OH 1-
Ca(OH)2
Writing Formulas for Ionic CompoundsExample: Write the correct formula for the following ionic compounds.
Zinc bromide
Aluminum carbonate
Iron (II) phosphate
Tin (IV) sulfate
Magnesium hydroxide
Writing Formulas for Ionic CompoundsExample: Write the correct formula for the following ionic compounds.
Sodium bicarbonate
Ammonium sulfate
Potassium phosphite
Sodium hypochlorite
Copper (I) oxide
Writing Formulas for Ionic Compounds Remember:
Use empirical formulas
Formulas must be electrically neutral
Do not show the charges of each ion in the final formula that you write
Use parentheses around polyatomic ions if more than one is present in the formula Do not use ( ) around monoatomic ions Do not use ( ) around a single
polyatomic ion
Naming Ionic Compounds Ionic compounds are named using the
cation name followed by the anion name
CaBr2 calcium bromideNaClO sodium hypochloriteMg3(PO4)2 magnesium phosphate
If the cation can form ions with more than one charge, you must specify the charge:
Fe2S3 iron (III) sulfidePbO2 lead (IV) oxide
Naming Ionic CompoundsExample: Name the following ionic
compounds.
Na2SO4
FeCl3
(NH4)3PO4
KClO4
Cu2CO3 Sn(SO4)2
Common “Household” Chemicals You are responsible for knowing the
names and formulas for the chemical present in:Baking soda
sodium bicarbonate NaHCO3
Table salt Sodium chloride NaCl
Bleach Sodium hypochlorite NaClO or NaOCl