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.