Upload
deirdre-gwen-webster
View
221
Download
3
Embed Size (px)
Citation preview
Molecules, Ions, and Molecules, Ions, and Their CompoundsTheir Compounds
Goals:
1. Know formulas for ionic and molecular compounds.
2. Name compounds.3. Understand some properties of ionic
compounds.4. Calculate and use molar mass.5. Calculate % composition for a compound and
derive formulas from experimental data.
What are compounds?What are compounds?What are molecules?What are molecules?
• COMPOUNDS
are a combination of 2 or more elements in definite _____________. The
character of each element is _________when forming a compound.
• MOLECULESare the smallest unit of a compound that retains the characteristics of the compound.
Compounds: Ionic and Compounds: Ionic and MolecularMolecular
NaCl, saltNaCl, saltNaCl, saltNaCl, salt
CHCH33CHCH22OH, ethanolOH, ethanol
What is a Molecular What is a Molecular Formula?Formula?
• Molecular Formulas describe the composition of molecules:
• Formula for glycine is Formula for glycine is CC22HH55NONO22• In one molecule there areIn one molecule there are
– 2 C atoms2 C atoms– 5 H atoms5 H atoms– 1 N atom1 N atom– 2 O atoms2 O atoms
Writing Molecular FormulasWriting Molecular Formulas
• Can also write glycine formula as
–H2NCH2COOH(condensed formula) to show atom ordering.
• or in the form of a structural formula:
C
H
H C
H
H
O
O HN
Molecular ModelingMolecular Modeling
• Representations of glycine:
Ball & stickBall & stick Space-fillingSpace-filling
Write structural formula of glycine:
What is Molecular Weight?What is Molecular Weight?What is Molar Mass?What is Molar Mass?
Molecular weight:Molecular weight: ______________ ______________
weights of all ________ in the molecule.weights of all ________ in the molecule.
Molar mass:Molar mass: molecular weight in molecular weight in ________________..
What is the molar mass of ethanol, C2H6O?
Molar MassMolar Mass
Students should become familiar with calculations and use of molar mass.
How many How many molesmoles of alcohol are there in a of alcohol are there in a “standard” can of beer if there are 21.3 g of C“standard” can of beer if there are 21.3 g of C22HH66O? O?
How many How many moleculesmolecules? How many C ? How many C atomsatoms??
1. Calculate the number of moles: This is a grams to moles conversion. Need to know how many grams are there per mol of ethanol.
2. Calculate the number of molecules:
3. Calculate the number of C atoms: There are 2 C per ethanol molecule.
Compounds: Ionic and Compounds: Ionic and MolecularMolecular
WaterWaterCaffeineCaffeineCitric acidCitric acid
NaClNaCl
How to know?How to know?MgBr2 CCl4
K2S H2O
CuSO4 C6H12O6
• 1. Most metal-containing compounds are ionic.
• 2. If there is no metal in the formula, it is likely that the compound is not ionic (except compounds from polyatomic ions based on nonmetals, ex: NH4NO3).
• Learn the formulas of polyatomic ions.
What are Ions?What are Ions?How are Ions formed?How are Ions formed?
• 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.
Forming IonsForming Ions
Predicting Ions ChargesPredicting Ions Charges
Look at Fig. 3.7 (page 105).
In general,Metals (Li) loose electrons to
become CATIONS.Nonmetals (F) gain electrons to
become ANIONS.
+3
-4 -2-3+1
+2
By losing or gaining e-, the atom has the By losing or gaining e-, the atom has the same number of e-’s as nearest same number of e-’s as nearest Group 8A Group 8A
atomatom..
Charges on Common IonsCharges on Common Ions-1
Charges on Monoatomic Charges on Monoatomic IonsIons
Students should become familiar with the charges of common ions.
Metals and their IonsMetals and their Ions
M ---> n e- + MM ---> n e- + Mn+n+
where n = periodic groupwhere n = periodic groupNa – Group 1Na – Group 1 NaNa++ sodium ion sodium ionMg – Group 2Mg – Group 2 MgMg2+2+ magnesium ionmagnesium ionAl – Group 3Al – Group 3 AlAl3+3+ aluminum ionaluminum ion
Transition metals --> MTransition metals --> M2+2+ or M or M3+3+ are commonare common
FeFe2+2+ iron(II) ioniron(II) ionFeFe3+3+ iron(III) ioniron(III) ion
Nonmetals and their IonsNonmetals and their Ions
NONMETAL + n e- ------> XNONMETAL + n e- ------> Xn-n-
where n = 8 - Group no.where n = 8 - Group no.
CC4-4-,carbide,carbide NN3-3-, nitride, nitride OO2-2-, oxide, oxide
SS2-2-, sulfide, sulfide
FF--, fluoride, fluoride
ClCl--, chloride, chloride
Group 7AGroup 6AGroup 4A Group 5A
BrBr--, bromide, bromide
II--, iodide, iodide
Name of Name of monoatomic anion monoatomic anion is derived by is derived by adding -ide to adding -ide to stemstem
Polyatomic IonsPolyatomic Ions
• Groups of atoms with a charge.Groups of atoms with a charge.• MEMORIZE MEMORIZE the names and formulas in the names and formulas in
Table 3.1, page 107.Table 3.1, page 107.
Students should become familiar with formulas, names, and charges of
polyatomic ions.
Polyatomic IonsPolyatomic Ions
Note: many O containing anions have names ending in –ate (or -ite).
Note: many O containing anions have names ending in –ate (or -ite).
Naming Polyatomic IonsNaming Polyatomic Ions
NHNH44++
ammonium ionammonium ion
One of the few common One of the few common polyatomic polyatomic cationscations
Compounds formed from Compounds formed from IonsIons
CATION CATION + + ANION ANION ---> ---> COMPOUNDCOMPOUND
CATION CATION + + ANION ANION ---> ---> COMPOUNDCOMPOUND
A neutral compound requires
equal number of+ and - charges.
A neutral compound requires
equal number of+ and - charges.
NaNa++ + Cl + Cl-- --> NaCl--> NaCl+1 + (-1) = 0 +1 + (-1) = 0
What are Ionic Compounds?What are Ionic Compounds?• Ionic compounds are composed of
ions.NH4
+
Cl-
ammonium chloride, NHammonium chloride, NH44ClCl
Students should become familiar with formulas and names ionic compounds.
Formation of Ionic Formation of Ionic CompoundsCompounds
MgMg2+2+ + NO + NO33-- ----> ---->
Mg(NOMg(NO33))22
magnesiummagnesium nitratenitrate
FeFe2+2+ + PO + PO443-3- ----> ---->
FeFe33(PO(PO44))22
iron(II) phosphateiron(II) phosphate
calcium fluoridecalcium fluoride
CaCa2+2+ + 2 F + 2 F-- ---> ---> CaFCaF22
Formation of Ionic Formation of Ionic CompoundsCompounds
• A metal atom A metal atom transfers an transfers an electron to a electron to a nonmetal.nonmetal.
• The resulting The resulting cation and anion cation and anion are attracted to are attracted to each other by each other by electrostatic electrostatic forcesforces..
Formation of Ionic Formation of Ionic CompoundsCompounds
The oppositely charged ions in ionic The oppositely charged ions in ionic compounds are attracted to one compounds are attracted to one another by another by ELECTROSTATIC FORCESELECTROSTATIC FORCES..
These forces are governed by These forces are governed by COULOMB’S LAWCOULOMB’S LAW..
Electrostatic Forces and Ionic Electrostatic Forces and Ionic CompoundsCompounds
• What happens to the attractive force What happens to the attractive force when the charge on the ion increases?when the charge on the ion increases?
• What happens to the attractive force What happens to the attractive force when the distance between ions when the distance between ions increases?increases?
Electrostatic ForcesElectrostatic ForcesCoulomb’s LawCoulomb’s Law
Importance of Coulomb’s Law.Importance of Coulomb’s Law.Why is the m.p. of MgO higher than Why is the m.p. of MgO higher than
that of NaCl?that of NaCl?
NaCl, NaNaCl, Na++ and Cl and Cl--,,m.p. 804 m.p. 804 ooCC
MgO, MgMgO, Mg2+2+ and O and O2-2-
m.p. 2800 m.p. 2800 ooCC
Melting PointMelting Point• Melting point is the temperature at which a
substance goes from solid to liquid.• In a solid: particles are fixed, in ionic solid
they are fixed by very strong electrostatic attractions.
• In a liquid: particles move.• In order to change the substance from
solid to liquid (get the particles moving) the particles need some energy: just enough to break the electrostatic attractions.
• The stronger the attraction, the more energy is needed to overcome it: a higher melting point results.
PracticePracticeSelect the compound with the higher melting
point:NaCl, AlN
KCl, CsI
Some general propertiesSome general properties
• The compound is ionic:– The compound would conduct electricity if
molten. – The compound dissolved in water it would be a
strong electrolyte (produce plenty of ions).– The compound would be expected to be a solid
at room temperature and pressure.– The compound would be expected to have a
relatively high melting point.• The compound is molecular:
– If the compound dissolved in water it would be a non-electrolyte.
– The compound would be expected to have a relatively low melting point.
Elements that exist as Elements that exist as MoleculesMolecules
Allotropes of Carbon
CC6060CC CC
Elements that exist asElements that exist asDiatomic MoleculesDiatomic Molecules
Elements that exist as Elements that exist as Polyatomic MoleculesPolyatomic Molecules
White P4 and polymeric red phosphorus
S8 sulfur molecules
What are Molecular What are Molecular Compounds?Compounds?
• Compounds without ions.
Methane, CH4
Carbon dioxide, CO2
Boron trichloride, BCl3
Molecular compoundsare formed from twoor more nonmetals.
Molecular compoundsare formed from twoor more nonmetals.
Students should become familiar with formulas and names of molecular
compounds.
PracticePractice• Which of the following are ionic, and which
are molecular? Give their name.
NaICCl4Ca(NO3)2
FeCl3NF3
NH4CH3COO
NaBr3
Empirical and Molecular Empirical and Molecular FormulasFormulas
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, C2H6O52.13% C13.15% H 34.72% O
Mass percentMass percent
• Expression of molecular composition in terms of the mass of each element in the compound relative to the total mass of the compound.
NONO22
Mass % N in NOMass % N in NO22 = =Mass of N in 1 mol NOMass of N in 1 mol NO22
Mass of 1 mol NOMass of 1 mol NO22
Percent CompositionPercent Composition
Consider some of the family of Consider some of the family of nitrogen-oxygen compounds:nitrogen-oxygen compounds:
NONO22, nitrogen dioxide and closely , nitrogen dioxide and closely related,related,
NONO, nitrogen monoxide (or nitric oxide)., nitrogen monoxide (or nitric oxide).
What is the weight percent of N and of O in NO2? In NO?
Students should become familiar with calculations of % weight,
empirical and molecular formulas.
What is the weight percent of N and of O in NO2? In NO?
How can Molecular Formulas How can Molecular Formulas be determined?be determined?
• Molecular formulas can be determined from chemical analysis or instrumental methods, such as mass spectrometry.
46
45
CH3CH2OH+
CH3CH2O+
31
CH2O+
Determining FormulasDetermining Formulas
In In chemical analysischemical analysis we determine we determine the % by weight of each element in a the % by weight of each element in a given amount of pure compound and given amount of pure compound and
derive the derive the EMPIRICAL EMPIRICAL or or SIMPLEST SIMPLEST formula.formula.
BenzeneBenzene
-Aromatic compound-Aromatic compound
CH
CHCH
CH
CHCH
CC66HH66 CHCH
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.
1. Calculate the number of moles of each constituent in 100 g of sample.
A compound of B and H is 81.10% B. What is its empirical formula?
2. Find the ratio of moles of elements in the compound. Take the ratio of moles of B and H. Always divide by the smallest number. Find a whole number ratio.
Deriving FormulasDeriving Formulas
• Steps from % composition to formula:
% A% A
% B% B
g Ag A
g Bg B
X mol AX mol A
X mol BX mol B
Convert weight Convert weight percent to masspercent to mass
Convert Convert mass to mass to molesmoles
Find mole Find mole ratioratio
x mol Ax mol Ay mol By mol B
Always divide the Always divide the larger number by larger number by the smaller one.the smaller one.Ratio gives formulaRatio gives formula
AAxxBByy
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/molCompare with the mass of B2H5 = 26.66
g/unit
1. Find the ratio of these masses.
Determine the MOLECULAR Formula Determine the MOLECULAR Formula from Combining Masses (see page from Combining Masses (see page
125).125).
Sn(s) + some ISn(s) + some I22(s) ---> (s) ---> SnISnIxx
Reaction of Sn and I2 is done using excess Sn.
Mass of Sn in the beginning = 1.056 gMass of iodine (I2) used = 1.947 g
Mass of Sn remaining = 0.601 g
Tin and Iodine CompoundTin and Iodine Compound
1. Find the mass of Sn (used in excess) that combined with 1.947 g I2 (limiting reactant).
2. Find moles of Sn used:
3. Now find the number of moles of I2 that combined with the mol Sn. Mass of I2 used was 1.947 g.
4. Calculate the mol of Iodine atoms:
5. Find the ratio of the number of moles of I and S that combined.
What are Hydrated What are Hydrated Compounds?Compounds?
• Hydrated compounds are those in which molecules of water are associated with the ions of the compound.
CoCl2 6H2O CoCl2
Anhydride
.
Hydrated CompoundsHydrated Compounds
Atoms in formula of compound:
CoCl2 6H2O.
PracticePractice
• Ten grams of each substance contains the largest number of moles?
H2O Kr BaCl2 H2OBr2
..
Using molar masses, calculate number of Using molar masses, calculate number of moles.moles.
Know that the Know that the larger the molar mass, larger the molar mass, the fewer number of molesthe fewer number of moles..
PracticePractice
• How many nitrate ions are found in 1.50 moles of calcium nitrate?
Particles in a mole?Avogadro’s number
RememberRemember
• Go over all the contents of your textbook.
• Practice with examples and with problems at the end of the chapter.
• Practice with OWL tutor.• Practice with the quiz on CD of
Chemistry Now.• Work on your assignment for Chapter
3.