Title: Compounds
1Compounds Molecules
Molecule The smallest identifiable unit that
retains the physical and chemical properties of
the pure substances.
Ethanol, C2H6O
Buckyball, C60
2Compounds Molecules
- COMPOUND is a combination of 2 or more elements
in definite ratios by mass. - The character of each element is lost when
forming a compound (e.g., think of NaCl). - MOLECULES are the smallest units of a compound
that retains the characteristics of the compound.
3MOLECULAR FORMULAS
- Formula for glycine is C2H5NO2
- (description of the composition)
- In one molecule there are
- 2 C atoms
- 5 H atoms
- 1 N atom
- 2 O atoms
4CONDENSED FORMULAS
- Formula for glycine is NH2CH2CO2H
- (composition and functional groups)
- In one molecule there are
- 1 NH2 (amine group)
- 1 CH2 group
- 1 CO2H group
5STRUCTURAL FORMULAS
- Show how the atoms are attached within a molecule
- The lines between atoms represent chemical bonds
that hold the atoms together.
6WRITING FORMULAS
- Can also write glycine as the condensed formula
H2NCH2COOH - showing functional groups (atom ordering and
connectivity) - or in the form of a structural formula
- showing how atoms are attached to each other
(bond orders) -
7MOLECULAR MODELING
An even higher level of structural detail
Drawing of glycine
Ball stick
Space-filling
8Resources for Molecular Modeling
- Modeling software
- CAChe (General Chemistry Interactive CD-ROM)
- Rasmol
- Molden
- Gaussview
- Maestro
9MOLECULAR WEIGHT AND MOLAR MASS
- Molecular weight sum of the atomic weights of
all atoms in the molecule. - Molar mass molecular weight in grams per mol.
10What is the molar mass of ethanol, C2H6O?
- 1 mol contains
- 2 moles of C (12.01 g C/1 mol) 24.02 g C
- 6 moles of H (1.01 g H/1 mol) 6.06 g H
- 1 mol of O (16.00 g O/1 mol) 16.00 g O
- TOTAL molar mass 46.08 g/mol
11Tylenol
C8H9NO2
151.2 g/mol
12Molar Mass
13How many moles of alcohol (C2H6O) are there in a
standard can of beer if there are 21.3 g of
C2H6O?
- (a) Molar mass of C2H6O 46.08 g/mol
- (b) Calc. moles of alcohol
14How many molecules of alcohol are there in a
standard can of beer if there are 21.3 g of
C2H6O?
We know there are 0.462 mol of C2H6O.
15How many atoms of C are there in a standard can
of beer if there are 21.3 g of C2H6O?
There are 2.78 x 1023 molecules. Each molecule
contains 2 C atoms. Therefore, the number of C
atoms is
16Molecular Ionic Compounds
NaCl
Heme
Molecular compounds consist of discrete
molecules Ionic compounds consist of discrete ions
17IONS AND IONIC COMPOUNDS
- IONS are atoms or groups of atoms with a positive
or negative charge. - Taking away an electron from an atom gives a
CATION with a positive charge - Adding an electron to an atom gives an ANION with
a negative charge.
18Forming Cations Anions
A CATION forms when an atom loses one or more
electrons.
An ANION forms when an atom gains one or more
electrons
F e- --gt F-
Mg --gt Mg2 2 e-
reduction
oxidation
19oxidation
reduction
20PREDICTING ION CHARGES
- In general
- metals (Mg) lose electrons ---gt cations
- nonmetals (F) gain electrons ---gt anions
21Charges on Common Ions
Anion chargegroup -8
Cation chargegroup
3
By losing or gaining e-, atom has same number of
electrons as nearest Group 8A atom.
22Predicting Charges on Monatomic Ions
23METALS
- M ---gt n e- Mn
- where n periodic group
- Na sodium ion
- Mg2 magnesium ion
- Al3 aluminum ion
- Transition metals --gt M2 or M3 are
common - Fe2 iron(II) ion
- Fe3 iron(III) ion
24NONMETALS
- NONMETAL n e- ------gt Xn- where n 8 -
Group no.
N3-, nitride
O2-, oxide
F-, fluoride
S2-, sulfide
Cl-, chloride
Br-, bromide
I-, iodide
25Ion Formation
- Reaction of aluminum and bromine
26POLYATOMIC IONSCD Screen 3.6
- Groups of atoms with a charge.
- MEMORIZE the names and formulas of common
polyatomic ions listed in Table 3.1, page 107
(next slide)
27(No Transcript)
28Polyatomic Ions
- NH4
- ammonium ion
- One of the few common polyatomic cations
29Polyatomic Ions (oxoanions)
NO3- nitrate ion
HNO3 nitric acid
Prefix per- and suffix ate largest Suffix
-ate greater of oxygen atoms Suffix -ite
smaller of oxygen atoms Prefix hypo- and suffix
ite smallest
30Polyatomic Ions
- SO42-
- sulfate ion
- SO32-
- sulfite ion
31Polyatomic Ions
- NO3-
- nitrate ion
- NO2-
- nitrite ion
32Polyatomic Ions
- CO32-
- carbonate ion
- HCO3-
- bicarbonate ion
- hydrogen carbonate
33Polyatomic Ions
- PO43-
- phosphate ion
- CH3CO2-
- acetate ion
34COMPOUNDS FORMED FROM IONS
CATION ANION ---gt COMPOUND
A neutral compd. requires equal number of
and - charges.
35IONIC COMPOUNDS
ammonium chloride, NH4Cl
36Some Ionic Compounds
Ca2 2 F- ---gt
CaF2
- Mg2 NO3- ----gt Mg(NO3)2
- magnesium nitrate
- Fe2 PO43- ----gt Fe3(PO4)2
- iron(II) phosphate
calcium fluoride
37Properties of Ionic CompoundsForming NaCl from
Na and Cl2
- A metal atom can transfer an electron to a
nonmetal. - The resulting cation and anion are attracted to
each other by electrostatic forces.
38Electrostatic Forces
- The oppositely charged ions in ionic compounds
are attracted to one another by ELECTROSTATIC
FORCES. - These forces are governed by COULOMBS LAW.
39Electrostatic Forces
As ion charge increases, the attractive force
_______________. As the distance between ions
increases, the attractive force
________________. This idea is important and will
come up many times in future discussions!
40Importance of Coulombs Law
NaCl, Na and Cl-, m.p. 804 oC
MgO, Mg2 and O2- m.p. 2800 oC
41ELEMENTS THAT EXIST AS MOLECULES
Allotropes of C
- See SCREEN 3.2 on the CD-ROM
42Screen 3.2
43ELEMENTS THAT EXIST AS DIATOMIC MOLECULES (gases)
44ELEMENTS THAT EXIST AS POLYATOMIC MOLECULES
S8 sulfur molecules
White P4 and polymeric red phosphorus
45Molecular CompoundsCompounds without Ions
CO2 Carbon dioxide
BCl3 boron trichloride
CH4 methane
46Naming Molecular Compounds
All are formed from two or more nonmetals.
CO2 Carbon dioxide
Ionic compounds generally involve a metal and
nonmetal (NaCl)
BCl3 boron trichloride
CH4 methane
47Empirical Molecular Formulas
- A pure compound always consists of the same
elements combined in the same proportions by
weight. - Therefore, we can express molecular composition
as PERCENT BY WEIGHT
Ethanol, C2H6O 52.13 C 13.15 H 34.72 O
48Percent Composition
- Consider some of the family of nitrogen-oxygen
compounds - NO2, nitrogen dioxide and closely related, NO,
nitrogen monoxide (or nitric oxide)
Chemistry of NO, nitrogen monoxide
49Percent Composition
- Consider NO2, Molar mass ?
- What is the weight percent of N and of O?
What are the weight percentages of N and O in NO?
50Determining Formulas
- In chemical analysis we determine the by weight
of each element in a given amount of pure
compound and derive the EMPIRICAL or SIMPLEST
formula. - PROBLEM A compound of B and H is 81.10 B.
What is its empirical formula?
51A compound of B and H is 81.10 B. What is its
empirical formula?
- Because it contains only B and H, it must contain
18.90 H. - In 100.0 g of the compound there are 81.10 g of B
and 18.90 g of H. - Calculate the number of moles of each
constitutent.
52A compound of B and H is 81.10 B. What is its
empirical formula?
- Calculate the number of moles of each element in
100.0 g of sample.
53A compound of B and H is 81.10 B. What is its
empirical formula?
- Now, recognize that atoms combine in the ratio of
small whole numbers - Find the ratio of moles of elements in the
compound.
54A compound of B and H is 81.10 B. What is its
empirical formula?
Take the ratio of moles of B and H.
Always divide by the smaller number.
- But we need a whole number ratio.
- 2.5 mol H/1.0 mol B 5 mol H to 2 mol B
- EMPIRICAL FORMULA B2H5
55A compound of B and H is 81.10 B. Its empirical
formula is B2H5. What is its molecular formula ?
- Is the molecular formula B2H5, B4H10, B6H15,
B8H20, etc.?
56A compound of B and H is 81.10 B. Its
empirical formula is B2H5. What is its molecular
formula?
- We need to do an EXPERIMENT to find the MOLAR
MASS. - Here experiment gives 53.3 g/mol
- Compare with the mass of B2H5
- 26.66 g/unit
- Find the ratio of these masses.
57How to Determine the molar mass?
58Mass Spectrum of Ethanol
Mass Spectrum of Ethanol (from the NIST site)
CH2O
31
CH3CH2O
45
CH3CH2OH
46
59Determine the formula of a compound of Sn and I
using the following data.
- Reaction of Sn and I2 is done using excess Sn.
- Mass of Sn in the beginning 1.056 g
- Mass of iodine (I2) used 1.947 g
- Mass of Sn remaining 0.601 g
60Tin and Iodine Compound
- Find the mass of Sn that combined with 1.947 g
I2. - Mass of Sn initially 1.056 g
- Mass of Sn recovered 0.601 g
- Mass of Sn used 0.455 g
- Find moles of Sn used
61Tin and Iodine Compound
- Now find the number of moles of I2 that combined
with 3.83 x 10-3 mol Sn. Mass of I2 used was
1.947 g.
How many moles of iodine atoms?
1.534 x 10-2 mol I atoms
62Tin and Iodine Compound
- Now find the ratio of number of moles of moles of
I and Sn that combined.
Empirical formula is SnI4