Transcript Chapter 3

Molecules, Compounds, and Chemical Equations
Compounds
 When two or more elements are
combined chemically, they are called
a compound.
 Just like letters of the alphabet can be
combined to form an endless number
of words, elements can be combined
to form an endless number of
compounds.
 Life would not possible without the
diversity of compounds.
Compounds
 Hydrogen, a diatomic and
colorless gas
 Oxygen, a diatomic and
colorless gas
 Water, a clear liquid which
is essential for most life
forms
Compounds
Compounds
 Most elements are not found by
themselves in nature, rather they
occur in compounds like NaCl or
MgO
 Some occur as diatomic molecules:
N2 , O2 , F2 , Cl2 , Br2 , and I2.
 Others like P and S are polyatomic.
 Only the metals of Gold, Copper, and
Silver can sometimes be found in
their pure state.
Molecular Elements
Chemical Bonds
 Compounds are held together by
one of two types of bonds.
 Ionic bonds are the electrostatic
attraction between cations and
anions.
 Covalent bonds are when two
atoms share at least a pair of
electrons.
Compounds
 A chemical formula is used to describe our
compounds.
 Uses subscripts after each element in the formula.
 Subscript of “1” is implied if no subscript.
 Empirical formula = simplest whole number ratio of the
elements in compound.
 Molecular formula = actual number of atoms bonded
together.
 Structural formula = shows how the atoms are bonded
together with lines representing the bonds.
Molecular Models
 A model may be used to represent a molecule.
 Ball-and-stick
 Space-filling
 No model is completely accurate!
Molecular View of Elements and Compounds
Classifying Elements & Compounds
• Atomic elements = elements whose particles are
•
•
•
single atoms
Molecular elements = elements whose particles
are multi-atom molecules
Molecular compounds = compounds whose
particles are molecules made of only nonmetals
Ionic compounds = compounds whose particles
are cations and anions
Ionic vs. Molecular
Propane – contains
individual C3H8
molecules
Table salt – contains
an array of Na+ ions
and Cl- ions
Learning Check
 Classifying each as either an Atomic element,
Molecular element, Molecular compound, or Ionic
compound.
 A) Formaldehyde, CH2O
 B) Red phosphorous, P4
 C) Cobalt, Co
 D) Magnesium chloride, MgCl2
Ionic Compounds
 Ionic compounds – are substances that contain both
cations and anions.
 Formulas are always empirical – lowest whole number
ratio of cations and anions.
 Writing ionic formulas – charges must cancel to yield a
neutral species.
 Most common charges for cations = +1, +2, or +3
 Most common charges for anions are -1, -2, or -3.
Ionic Compounds
M,X
+1
+2
+3
-1
MX
MX2
MX3
-2
M 2X
MX
M2X3
-3
M3X
M3X2
MX
Ionic Compounds
 Learning Check
 Write the correct formula between the ions of…
 A) Ca and Br
 B) K and S
 C) Li and N
 D) Al and O
 E) Mg and P
Naming Inorganic Compounds
 Chemical Nomenclature - the systematic method of
naming chemical compounds.
 Different system for naming Ionic and Molecular
compounds.
 Ionic = cation (usually a metal) with an anion (usually
a non-metal.
 Molecular = two or more non-metals or metalloid with
a non-metal.
 Identify compound BEFORE going to the rules!!!
Ionic or Molecular
 Learning Check…
 Identify as Ionic or Molecular
 A) Na2S
 B) PCl3
 C) SiH4
 D) FeBr3
 E) ZnO
 F) CCl4
Polyatomic Ions
 An ion composed of two or more elements with a net






charge.
Only one is a cation – NH4+ = ammonium ion.
All the rest are anions.
Any time a polyatomic ion is present, then the compound
is ionic.
Ex) Na2SO4, MgCO3, NH4Cl
When more than one polyatomic ion is needed to balance
charges, then use (poly)x.
Ex) Al(NO3)3, (NH4)2S
Naming Ionic Compounds
 Two subcategories:
 Metals with only one valence (mostly the main group
metals)
 Metals with more than one possible valence charge.
 Metals with only one valence
1. Name the metal first
2. Name the non-metal second and change its suffix to

ide.
For polyatomic ions, they ALWAYS keep their same
name – DO NOT CHANGE TO ide ending.
Learning Check
 What is the name of…
 A) NaBr
 B) MgSO4
 C) K2S
 D) Li3PO4
Naming Ionic Compounds

1.
2.

Metals with more than one valence
Name metal first followed by its valence in Roman
Numerals and in ( ). This means that you will have to
figure out the charge for that metal based on what it is
bonded to.
Name the non-metal second and change the suffix to ide.
As before, polyatomics remain the same.
Learning Check
 What is the name of…
 A) Cu2O
 B) Fe2S3
 C) Mn(NO3)2
 D) Co3(PO4)2
Naming Molecular Compounds

1.
2.
3.

Remember, these contain only non-metals or a
metalloid with a non-metal.
Name the first non-metal in the formula.
Name the second non-metal in the formula and
change the suffix to ide.
Add prefixes for all subscripts - except if the first one
is a “1”.
1 = mono, 2 = di, 3 = tri, 4 = tetra, 5 = penta, and 6 =
hexa.
Learning Check
 What is the name of…
 A) CS2
 B) PCl5
 C) AsBr3
 D) N2O4
 E) N2O
Nomenclature Overview
Compound
Ionic or
Molecular?
Ionic
Metal
Fixed charge
Molecular
Metal
Variable
Charge
Learning Check
 What is the name of…
 A) NiCl2
 B) K2CrO4
 C) Cl2O
 D) SF4
 E) (NH4)2SO4
Naming Acids
 Acids are molecular compounds that release an H+
when added to water.
 Formula starts with an “H”.
 Binary acids = H with one other element.
 Hydro + base name of non-metal + ic + acid
 HCl = hydrochloric acid
 Oxoacids = HXOy
 Polyatomic ion ends in –ate, then suffix changes to –ic
 Polyatomic ion ends in –ite, then suffix changes to -ous
Learning Check
 What is the name of…
 A) HBr
 B) HNO3
 C) H2SO3
 D) H3PO4
Quantitative Aspect
 A chemical formula also has a quantitative aspect.
 A Formula Weight for an element or compound is
found using the periodic table.
 Formula weights can refer to a single element’s weight or
an ionic compound.
 Molecular weight refers to a molecular compound’s
weight.
 Weights from periodic table should be rounded to the
nearest 0.1 amu at the bare minimum!
Molar Mass
 The molar mass of any compound is equal to the sum
of the atomic weights expressed in grams.
 Ex) The molar mass of CO2 is 44.0 grams.
 Thus, one mole of CO2 = 44.0 grams.
 1 mol CO2 = 6.02 x 1023 molecules.
 Calculate the molar mass for…
 A) PCl3
 B) C6H12O6
 C) Fe2(SO4)3
Using Molar Masses
 A molar mass can be used to convert grams to moles or
moles to grams.
 Calculate:
 A) the moles present in 2.85g of CO2
 B) the grams present in 0.552 moles of NH3
 C) the number of molecules present in 0.255g of H2O
 D) the number of O atoms in 3.00g of C6H12O6
Percent Composition
 A formula weight can be used to calculate the mass
percentage of any element in the formula by:
Mass % of A =
# atoms of A  atomic mass of A
 100
formula weight of compound
 This is one place to also test nomenclature!
 Find the mass percent of each element in the
compound Calcium nitrate.
Empirical Formulas
 We can use moles to find an empirical (simplest)
formula from mass percentages by:
Assume a 100 gram sample (%  grams).
2. Convert grams of each element to moles use the formula
weights.
3. Divide each mole amount by the smallest one.
4. Using a multiplier to eliminate fractions like: 0.25, 0.33,
0.50, 0.67, and 0.75.
1.
Empirical Formulas
 A compound contains 17.6% Na, 39.7% Cr, and 42.7%
O by mass. What is its empirical formula?
Molecular Formulas
 An empirical formula may not be the actual formula
since molecular formulas do not have to be the lowest
whole number subscripts.
 The multiplier, n, can be found if we know the overall
molecular weight of the compound.
molecular weight
n=
empirical weight
 A compound is contains 40.9% C, 4.6% H, and 54.5%
O by mass with a molecular weight of about 176g/mol.
What is the molecular formula for this compound?
Combustion Analysis
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Tro: Chemistry:
A Molecular Approach, 2/e
Combustion Analysis
 Combustion of a 0.8233 g sample of a compound
containing only carbon, hydrogen, and oxygen
produced the following:
CO2 = 2.445 g
H2O = 0.6003 g
 Determine the empirical formula of the compound
Chemical Equations
 Chemical reactions are represented in a concise
method by a chemical equation.
 Ex) 2 H2(g) + O2(g)
2 H2O(l)
Reactants
Products
Chemical Equations
 Ex) 2 H2(g) + O2(g)
Phase Symbols
2 H2O(l)
Coefficient
Balancing an Equation
 A subscript in a chemical formula tells us how many of
each type of atom are in the compound.
 Ex) C6H12O6
 Subscripts cannot be altered!!!
 Atoms can be created nor destroyed in a chemical
reaction.
 Thus, we balance a reaction by adding coefficients in
front of each substance.
Balancing an Equation
 Balance by inspection.
 Use a tally sheet.
 Start with elements that occur once on each side.
 Combustion – do C, then H, then O.
 Balance each reaction…
 __ Al + __ Cl2  __ AlCl
 __ H3PO3  __ H3PO4 + __ PH3
Balancing an Equation
 __ Na3PO4 + __ CaBr2  __ Ca3(PO4)2 + __ NaBr
 __ C3H8 + __ O2  __ CO2 + __ H2O
 __ C4H8O + __ O2  __ CO2 + __ H2
Classifying Compounds
Organic vs. Inorganic
 In the 18th century, compounds from living things were
called organic; compounds from the nonliving
environment were called inorganic
 Organic compounds easily decomposed and could not
be made in the 18th-century lab
 Inorganic compounds very difficult to decompose, but
able to be synthesized
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Tro: Chemistry:
A Molecular Approach, 2/e
Modern Classifying Compounds
Organic vs. Inorganic
 Today we commonly make organic compounds in the
lab and find them all around us
 Organic compounds are mainly made of C and H,
sometimes with O, N, P, S, and trace amounts of other
elements
 The main element that is the focus of organic
chemistry is carbon
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Tro: Chemistry:
A Molecular Approach, 2/e
Carbon Bonding
 Carbon atoms bond almost exclusively covalently
 compounds with ionic bonding C are generally inorganic
 When C bonds, it forms four covalent bonds
 4 single bonds, 2 double bonds, 1 triple + 1 single, etc.
 Carbon is unique in that it can form limitless chains of C
atoms, both straight and branched, and rings of C atoms
Carbon Bonding
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Tro: Chemistry:
A Molecular Approach, 2/e
Classifying Organic Compounds
 There are two main categories of
organic compounds,
hydrocarbons and
functionalized hydrocarbons
 Hydrocarbons contain only C
and H
 When all C-C bonds are single
bonds, they are called alkanes.
 Formula for any alkane is:
CnH2n+2.
Names of Alkanes
 CH4 = Methane
 C2H6 = Ethane
 C3H8 = Propane
 C4H10 = Butane
 C5H12 = Pentane
 C6H14 = Hexane
 C7H16 = Heptane
 C8H18 = Octane
Functional Groups
Family
Alcohol
Ether
Aldehyde
Ketone
Carboxylic Acid
Ester
Amine
Name ends w/
Generic
Example
Name