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Compounds

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Title: COMPOUNDS AND MOLECULES Author: J. Kotz Last modified by: Victor S. Batista Created Date: 6/11/1996 9:53:30 AM Document presentation format – PowerPoint PPT presentation

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Title: Compounds


1
Compounds Molecules
Molecule The smallest identifiable unit that
retains the physical and chemical properties of
the pure substances.
Ethanol, C2H6O
Buckyball, C60
2
Compounds 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.

3
MOLECULAR 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

4
CONDENSED 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

5
STRUCTURAL FORMULAS
  • Show how the atoms are attached within a molecule
  • The lines between atoms represent chemical bonds
    that hold the atoms together.

6
WRITING 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)

7
MOLECULAR MODELING
An even higher level of structural detail
Drawing of glycine
Ball stick
Space-filling
8
Resources for Molecular Modeling
  • Modeling software
  • CAChe (General Chemistry Interactive CD-ROM)
  • Rasmol
  • Molden
  • Gaussview
  • Maestro

9
MOLECULAR 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.

10
What 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

11
Tylenol
  • Formula
  • Molar mass

C8H9NO2
151.2 g/mol
12
Molar Mass
13
How 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

14
How 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.
  • 2.78 x 1023 molecules

15
How 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
  • 5.57 x 1023 C atoms

16
Molecular Ionic Compounds
NaCl
Heme
Molecular compounds consist of discrete
molecules Ionic compounds consist of discrete ions
17
IONS 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.

18
Forming 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
19
oxidation
reduction
20
PREDICTING ION CHARGES
  • In general
  • metals (Mg) lose electrons ---gt cations
  • nonmetals (F) gain electrons ---gt anions

21
Charges 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.
22
Predicting Charges on Monatomic Ions
23
METALS
  • 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

24
NONMETALS
  • NONMETAL n e- ------gt Xn- where n 8 -
    Group no.

N3-, nitride
O2-, oxide
F-, fluoride
S2-, sulfide
Cl-, chloride
Br-, bromide
I-, iodide
25
Ion Formation
  • Reaction of aluminum and bromine

26
POLYATOMIC 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)
28
Polyatomic Ions
  • NH4
  • ammonium ion
  • One of the few common polyatomic cations

29
Polyatomic 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
30
Polyatomic Ions
  • SO42-
  • sulfate ion
  • SO32-
  • sulfite ion

31
Polyatomic Ions
  • NO3-
  • nitrate ion
  • NO2-
  • nitrite ion

32
Polyatomic Ions
  • CO32-
  • carbonate ion
  • HCO3-
  • bicarbonate ion
  • hydrogen carbonate

33
Polyatomic Ions
  • PO43-
  • phosphate ion
  • CH3CO2-
  • acetate ion

34
COMPOUNDS FORMED FROM IONS
CATION ANION ---gt COMPOUND
  • Na Cl- --gt NaCl

A neutral compd. requires equal number of
and - charges.
35
IONIC COMPOUNDS
ammonium chloride, NH4Cl
36
Some 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
37
Properties 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.

38
Electrostatic Forces
  • The oppositely charged ions in ionic compounds
    are attracted to one another by ELECTROSTATIC
    FORCES.
  • These forces are governed by COULOMBS LAW.

39
Electrostatic Forces
  • COULOMBS LAW

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!
40
Importance of Coulombs Law
NaCl, Na and Cl-, m.p. 804 oC
MgO, Mg2 and O2- m.p. 2800 oC
41
ELEMENTS THAT EXIST AS MOLECULES
Allotropes of C
  • See SCREEN 3.2 on the CD-ROM

42
Screen 3.2
43
ELEMENTS THAT EXIST AS DIATOMIC MOLECULES (gases)
44
ELEMENTS THAT EXIST AS POLYATOMIC MOLECULES
S8 sulfur molecules
White P4 and polymeric red phosphorus
45
Molecular CompoundsCompounds without Ions
CO2 Carbon dioxide
BCl3 boron trichloride
CH4 methane
46
Naming 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
47
Empirical 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
48
Percent 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
49
Percent 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?
50
Determining 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?

51
A 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.

52
A 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.

53
A 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.

54
A 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

55
A 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.?

56
A 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.
  • Molecular formula B4H10

57
How to Determine the molar mass?
  • Mass spectrometer

58
Mass Spectrum of Ethanol
Mass Spectrum of Ethanol (from the NIST site)
CH2O
31
CH3CH2O
45
CH3CH2OH
46
59
Determine 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

60
Tin 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

61
Tin 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
62
Tin and Iodine Compound
  • Now find the ratio of number of moles of moles of
    I and Sn that combined.

Empirical formula is SnI4
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