Upload
dangdat
View
223
Download
3
Embed Size (px)
Citation preview
Maurizio CasarinA.A. 2017 - 2018
Fondamenti di Chimica
Fondamenti di Chimica & Educazione AmbientaleLecture 3
Maurizio CasarinA.A. 2017 - 2018
Fondamenti di Chimica
Compounds and MoleculesPure substances composed of two or more different
elements are called compounds.Compounds have definite percent composition
of their combining elements.
Maurizio CasarinA.A. 2017 - 2018
Fondamenti di Chimica
H2O2 CH3CH2Cl P4O10
CH3CH(OH)CH3 HCO2H
Some molecules
Maurizio CasarinA.A. 2017 - 2018
Fondamenti di Chimica
z Atoms of almost all elements can gain or lose electrons to form charged species called ions.
z Compounds composed of ions are known as ionic compounds.
u Metals tend to lose electrons to formpositively charged ions called cations.
u Non-metals tend to gain electrons to formnegatively charged ions called anions.
Ionic compounds
Maurizio CasarinA.A. 2017 - 2018
Fondamenti di Chimica
Extended array of Na+ and Cl- ions
Sodium chloride
Maurizio CasarinA.A. 2017 - 2018
Fondamenti di Chimica
Halothane C2HBrClF3
M(C2HBrClF3) = 2MC + MH + MBr + MCl + 3MF
= (2 × 12.01) + 1.01 + 79.90 + 35.45 + (3 × 19.00) = 197.38 g/mol
Mole ratio nC/nhalothane
Mass ratiomC/mhalothane
Chemical Composition
Maurizio CasarinA.A. 2017 - 2018
Fondamenti di Chimica
Calculating the Mass Percent Composition of a Compound
Calculate the molecular massM(C2HBrClF3) = 197.38 g/mol
For one mole of compound, formulate the mass ratio and convert to percent:
%C = (2×12.01)g
197.38g ×100% =12.17%
Maurizio CasarinA.A. 2017 - 2018
Fondamenti di Chimica
%C =(2 ×12.01)g
197.38g×100% = 12.17%
%H =1.01g
197.38g×100% = 0.51%
%Br = 79.90g197.38g
×100% = 40.48%
%Cl = 35.45g197.38g
×100% = 17.96%
%F =(3×19.00)g
197.38g×100% = 28.88%
Calculating the Mass Percent Composition of a Compound
Maurizio CasarinA.A. 2017 - 2018
Fondamenti di Chimica
1. Choose an arbitrary sample size (100g).2. Convert masses to amounts in moles.3. Write a formula.4. Convert formula to small whole numbers.5. Multiply all subscripts by a small whole number to
make the subscripts integral.
5 Step approach:
Empirical formula
Maurizio CasarinA.A. 2017 - 2018
Fondamenti di Chimica
Determining the Empirical and Molecular Formulas of aCompound from Its Mass Percent Composition.
Dibutyl succinate is an insect repellent used againsthousehold ants and roaches. Its composition is 62.58% C,9.63% H and 27.79% O. Its experimentally determinedmolecular mass is 230 u. What are the empirical andmolecular formulas of dibutyl succinate?
Dibutyl succinate is an insect repellent used againsthousehold ants and roaches. Its composition is 62.58% C,9.63% H and 27.79% O. Its experimentally determinedmolecular mass is 230 u. What are the empirical andmolecular formulas of dibutyl succinate?
Maurizio CasarinA.A. 2017 - 2018
Fondamenti di Chimica
Step 1: Determine the mass of each element in a 100g sample.
C 62.58 g
Determining the Empirical and Molecular Formulas of a Compound from Its Mass Percent Composition.
O 27.79 gH 9.63 g
Maurizio CasarinA.A. 2017 - 2018
Fondamenti di Chimica
Step 2: Convert masses to amounts in moles.
Step 3: Write a tentative formula.
Step 4: Convert to small whole numbers.
C5.21H9.55O1.74
C2.99H5.49O
Determining the Empirical and Molecular Formulas of a Compound from Its Mass Percent Composition.
�
nC = 62.58gC×1molC
12.011gC= 5.210molC
nH = 9.63gH×1molH
1.008gH= 9.55molH
nO = 27.79gO×1molO
15.999gO= 1.737molO
Maurizio CasarinA.A. 2017 - 2018
Fondamenti di Chimica
Step 5: Convert to a small whole number ratio.
Multiply × 2 to get C5.98H10.98O2
The empirical formula is C6H11O2
Step 6: Determine the molecular formula.
Empirical formula mass is 115 u.Molecular formula mass is 230 u.
The molecular formula is C12H22O4
Determining the Empirical and Molecular Formulas of a Compound from Its Mass Percent Composition.
Maurizio CasarinA.A. 2017 - 2018
Fondamenti di Chimica
Metals tend to lose electrons.
Na D Na+ + e-
Non-metals tend to gain electrons.
Cl + e- D Cl-
Reducing agents Oxidizing agents
We use the Oxidation State to keep track of the number ofelectrons that have been gained or lost by an element.
Oxidation States
Maurizio CasarinA.A. 2017 - 2018
Fondamenti di Chimica
1. The oxidation state (OS) of an individual atom in a free element is 0.2. The total of the OS in all atoms in:
i. Neutral species is 0.ii. Ionic species is equal to the charge on the ion.
3. In their compounds, the alkali metals and the alkaline earths have OS of +1 and +2 respectively.
4. In compounds the OS of fluorine is always –15. In compounds, the OS of hydrogen is usually +16. In compounds, the OS of oxygen is usually –2.7. In binary (two-element) compounds with metals:
i. Halogens have OS of –1,ii. Group 16 have OS of –2 andiii. Group 15 have OS of –3.
Rules for Oxidation States
Maurizio CasarinA.A. 2017 - 2018
Fondamenti di Chimica
Anions (- Q):Groups 15, 16, 17 (VA, VIA, VIIA)Cations (+ Q):Groups 1, 2, 3 (IA, IIA, IIIA)
Maurizio CasarinA.A. 2017 - 2018
Fondamenti di Chimica
Assigning Oxidation States.What is the oxidation state of the underlined element in each of the following? a) P4; b) Al2O3; c) MnO4
-; d) NaH
a) P4 is an element. P OS = 0 .
b) Al2O3: O is –2. O3 is –6. Since (+6)/2=(+3), Al OS = +3.
c) MnO4-: net OS = -1, O4 is –8. Mn OS = +7.
d) NaH: net OS = 0, rule 3 beats rule 5, Na OS = +1 and H OS = -1.
Maurizio CasarinA.A. 2017 - 2018
Fondamenti di Chimica
Naming Compounds
Trivial names are used for common compounds.
A systematic method of naming compounds is known as a systemof nomenclature.
Organic compoundsInorganic compounds
Maurizio CasarinA.A. 2017 - 2018
Fondamenti di Chimica
Binary Compounds of Metals and Nonmetals
NaCl = sodium chloride
name is unchanged
“ide” endingelectrically neutral
MgI2 = magnesium iodide
Al2O3 = aluminum oxide
Na2S = sodium sulfide
Inorganic Nomenclature
Maurizio CasarinA.A. 2017 - 2018
Fondamenti di Chimica
Molecular compoundsusually write the positive OS element first.HCl hydrogen chloride
mono 1 penta 5
di 2 hexa 6
tri 3 hepta 7
tetra 4 octa 8
Some pairs form more than one compound
Binary Compounds of Two Non-metals
Maurizio CasarinA.A. 2017 - 2018
Fondamenti di Chimica
Naming Binary Compounds of the Non-metals
Named in order of increasing group number
N2O4 Dinitrogen tetroxide
Sulfur hexafluoride
N2O Dinitrogen oxide
SF6
Maurizio CasarinA.A. 2017 - 2018
Fondamenti di Chimica
Emphasize the fact that a molecule is an acid by altering the name.
HCl hydrogen chloride hydrochloric acid
HF hydrogen fluoride hydrofluoric acid
Acids produce H+ when dissolved in water.
They are compounds that ionize in water.
Binary Acids
Maurizio CasarinA.A. 2017 - 2018
Fondamenti di Chimica
Polyatomic ions are very common. Here are a few:
ammonium ion NH4+ acetate ion C2H3O2
-
carbonate ion CO32- hydrogen carbonate HCO3
-
hypochlorite ClO- phosphate PO43-
chlorite ClO2- hydrogen phosphate HPO4
2-
chlorate ClO3- sulfate SO4
2-
perchlorate ClO4- hydrogensulfate HSO4
-
Polyatomic Ions
Maurizio CasarinA.A. 2017 - 2018
Fondamenti di Chimica
Gaining (anion) and Losing (cation)Electrons to attain Inert gas electronic
structure
Ionic Bonding:
Maurizio CasarinA.A. 2017 - 2018
Fondamenti di Chimica
When an atom gainselectrons it becomesan anion.
Anion are larger thanthe neutral atom.
When an atomloses electrons itbecomes a cation.
Cations are smallerthan the neutralatom.
Maurizio CasarinA.A. 2017 - 2018
Fondamenti di Chimica
The attractive force between + and -charges is called a coulombic attraction
Force of attraction = KQ1×Q2
d2
Maurizio CasarinA.A. 2017 - 2018
Fondamenti di Chimica
Predict the ionic bond strengthof the following ionic bonds.
Maurizio CasarinA.A. 2017 - 2018
Fondamenti di Chimica
Consider a cation and an anion
Na Cl
NaCl
Mg Cl Cl
MgCl2
Maurizio CasarinA.A. 2017 - 2018
Fondamenti di Chimica
How to write formulasfor ionic compounds
1. Identify ions
2.“Cross” charges
3. Write formula1 2
Charge is Conserved: The + = - !
Maurizio CasarinA.A. 2017 - 2018
Fondamenti di Chimica
Naming Ionic CompoundsCations are named as the metal + “ion”
Na+ = sodium ion
Multicharged ions
Stock SystemMetal (Charge in Roman Numerals)
“ion”Cu1+ Cu2+
Copper(I) ion Copper(II) ion
Maurizio CasarinA.A. 2017 - 2018
Fondamenti di Chimica
MgBr2 Magnesium bromide
Fe2O3 Iron(III) oxide
Ca3(PO4)2 Calcium phosphate
Naming Ionic Compounds
Maurizio CasarinA.A. 2017 - 2018
Fondamenti di Chimica
Compounds and Molecules
Some compounds are composed of molecules.
Maurizio CasarinA.A. 2017 - 2018
Fondamenti di Chimica
Sharing electrons to attain inertgas electron configurations.E
d
Covalent Bonding:
Maurizio CasarinA.A. 2017 - 2018
Fondamenti di Chimica
Organic compounds abound in natureFats, carbohydrates and proteins are foods.
Propane, gasoline, kerosene, oil.
Drugs and plastics
Carbon atoms form chains and rings and act as the framework of molecules.
Naming Organic Compounds
Maurizio CasarinA.A. 2017 - 2018
Fondamenti di Chimica
Molecular Structure
The arrangement of atoms in a molecule
Isomers:
Same number of constituent atoms BUT
different arrangements.
Maurizio CasarinA.A. 2017 - 2018
Fondamenti di Chimica
Isomerism
Structural
Stereo
Optical
Geometrical
Positional
Functional
Chain
Maurizio CasarinA.A. 2017 - 2018
Fondamenti di Chimica
Chain Isomers
n-pentane
2-methylbutane
2,2-dimethylpropane
C5H12
Maurizio CasarinA.A. 2017 - 2018
Fondamenti di Chimica
Positional Isomers
Propan-1-olo
Propan-2-olo
C3H7OH
Maurizio CasarinA.A. 2017 - 2018
Fondamenti di Chimica
Positional Isomers
2-Methylphenol 4-Methylphenol3-Methylphenol
C7H7OH
Maurizio CasarinA.A. 2017 - 2018
Fondamenti di Chimica
Functional Isomers
Ethanol Methoxymethane
C2H6O
Alcohols have the hydroxyl group, –OHEthers have the functional group R–O–R'
Maurizio CasarinA.A. 2017 - 2018
Fondamenti di Chimica
Functional Isomers
Propanal
C3H6O
Aldehydes and ketones have the carbonyl group C=O. Inaldehydes C is attached either to 1 or 2 H atoms; in ketones Cis attached to two carbon atoms.
Propanone
Maurizio CasarinA.A. 2017 - 2018
Fondamenti di Chimica
Isomerism
Structural
Stereo
Optical
Geometrical
Positional
Functional
Chain
Maurizio CasarinA.A. 2017 - 2018
Fondamenti di Chimica
Geometrical Isomers
Geometrical isomerism is an example of stereo-isomerism. This occurs when substances have thesame molecular formula, but a different arrangementof their atoms in space.
Geometrical isomerism can happen if:i) There is a C=C bond in the moleculeii) The molecule has a ringiii) The molecule has a >C=N bond
Maurizio CasarinA.A. 2017 - 2018
Fondamenti di Chimica
Geometrical IsomersC4H8
Cis-But-2-ene Trans-But-2-ene
Maurizio CasarinA.A. 2017 - 2018
Fondamenti di Chimica
trans-Pt(NH3)2Cl2
cis-Pt(NH3)2Cl2
Geometrical Isomers
Maurizio CasarinA.A. 2017 - 2018
Fondamenti di Chimica
cis-Pt(NH3)Cl2Br trans-Pt(NH3)Cl2Br
Two isomers
Geometrical Isomers
Maurizio CasarinA.A. 2017 - 2018
Fondamenti di Chimica
ClN
Cl
Pt
N
ClCl
ClN
Cl
Pt
Cl
NCl
transTwo isomers
cis
Geometrical Isomers
Maurizio CasarinA.A. 2017 - 2018
Fondamenti di Chimica
Cl N
Cl
Pt
Cl
N N
Cl N
Cl
Pt
N
NCl
facTwo isomers
mer
Geometrical Isomers
Maurizio CasarinA.A. 2017 - 2018
Fondamenti di Chimica
Optical IsomersOptical isomerism is an example of stereo-isomerism. It occurswhen substances have the same molecular and structuralformula, but one cannot be superimposed on the other. Thedifferent forms are called enantioners.
optical isomerism
non-superimposable mirror images
Maurizio CasarinA.A. 2017 - 2018
Fondamenti di Chimica
Optical Isomers
Optical isomers can occur when there is anasymmetric carbon atom; i.e. a C atom bonded to fourdifferent groups.