Ch04 lecpptchem1012011f

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Chapter 4: Chemical Chapter 4: Chemical BondsBonds

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Overview of Chapter 4Overview of Chapter 4 Electron configuration- valence electrons and stability.Electron configuration- valence electrons and stability. Electron-dot structures of atoms and ions; use to Electron-dot structures of atoms and ions; use to

describe reactions.describe reactions. Bonding in compounds: Ionic and covalent. Bonding in compounds: Ionic and covalent. Nomenclature of ionic and covalent compounds. Nomenclature of ionic and covalent compounds. Electronegativity. Electronegativity. Polar versus nonpolar compounds. Polar versus nonpolar compounds. Writing electron-dot structures of molecules. Writing electron-dot structures of molecules. Simple geometries of molecules. Simple geometries of molecules. Intermolecular forces in states of matter and in mixtures: Intermolecular forces in states of matter and in mixtures:

Dipole forces, hydrogen bonding, dispersion forces, Dipole forces, hydrogen bonding, dispersion forces, forces in solutions. forces in solutions.

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Bonding and Valence ElectronsBonding and Valence ElectronsForces that hold atoms together within a molecule, or ions together in crystals. Involve valence electrons = Outermost electrons.Inner electrons (core electrons) are generally not involved in bonding. Electron configuration- arrangement of electrons.

Valence electrons +

Core electrons06:33 PM06:33 PM

Noble Gas ConfigurationsNoble Gas Configurations

ExampleExample: :

Sodium (Na) losing an electron-Sodium (Na) losing an electron-

11p

Na: 11 e-1

lost e-1

+

The sodium ion and neon are isoelectronic- They have the same

electron configuration.

Na+1: 10 e-1

11p

Ne: 10 e-1

10p

Noble Gas ConfigurationsNoble Gas Configurations

ExampleExample: :

Chlorine (Cl) gaining an electron-Chlorine (Cl) gaining an electron-

17p

Cl: 17 e-1

gained e-1

+

Are the chlorine ion and argon isoelectronic?.

Cl-1: 18 e-1

17p

Ar: 18 e-1

18p

Ar: 18 e-1

Electron-Dot StructuresElectron-Dot Structures Electron-dot structures (EDSs) = Lewis-dot Electron-dot structures (EDSs) = Lewis-dot

structures (LDSs)?structures (LDSs)? Represent the no. of valence eRepresent the no. of valence e -1-1 around an atom (dots around an atom (dots

around symbol). around symbol). Example 1Example 1: Give the electron-dot structure for sodium. : Give the electron-dot structure for sodium.

What is the symbol for sodium?What is the symbol for sodium?NaNa

How many valence electrons does it contain?How many valence electrons does it contain?11

Write the symbol, then place electrons Write the symbol, then place electrons around the symbol (in pairs if possible). around the symbol (in pairs if possible).

Na

Electron-Dot Structures of AtomsElectron-Dot Structures of Atoms Give the electron-dot structure for the Give the electron-dot structure for the

following:following:

2.) K 2.) K 3.) Mg 3.) Mg

4.) Al 4.) Al 5.) O 5.) O

6.) Br 6.) Br

MgK

Al

Br

O

More on Electron ConfigurationsMore on Electron Configurations

Noble gases are most stable group of Noble gases are most stable group of elements (least reactive) Why? elements (least reactive) Why?

8 valence electrons = stable octet 8 valence electrons = stable octet

Stable electron configuration. Stable electron configuration.

Octet rule- Atoms attempt to obtain 8 Octet rule- Atoms attempt to obtain 8 valence electrons.valence electrons.

Exceptions: Group 1A, 2A, 3A elements Exceptions: Group 1A, 2A, 3A elements and helium. and helium.

Electron-Dot Structures of IonsElectron-Dot Structures of Ions

Na

11p

Na: 11 e-1

lost e-1

+

Na+1: 10 e-1

11p

Na+1

Example: Sodium forming sodium ion.Example: Sodium forming sodium ion.

Electron-Dot Structures of IonsElectron-Dot Structures of Ions

Example: Chlorine forming chloride ion.Example: Chlorine forming chloride ion.

17p

Cl: 17 e-1

gained e-1

+

Cl-1: 18 e-1

17p

Cl Cl -1

Ionic BondsIonic Bonds

A chemical bond between two ions;A chemical bond between two ions;TTransfer ransfer of electrons between a of electrons between a metal metal

and a and a nonmetalnonmetal. . Ionic compounds contain ionic bonds; Ionic compounds contain ionic bonds;

usually crystals. usually crystals. Very strong bond indeed!Very strong bond indeed!

Sodium and Chlorine: Boom!Sodium and Chlorine: Boom!

Example 1: Sodium will react with chlorine Example 1: Sodium will react with chlorine to form sodium chloride (NaCl). to form sodium chloride (NaCl).

Na + Cl ---- -----> NaClNa + Cl ---- -----> NaCl

Na Na+1Cl Cl -1+

Ionic CompoundsIonic Compounds

Example 2: A potassium atom reacts with a Example 2: A potassium atom reacts with a bromine atom to form potassium bromide bromine atom to form potassium bromide (KBr). (KBr).

K + Br K + Br KBr KBr

K Br+ K+1 Br -1+

Ionic CompoundsIonic Compounds

Example 3: A potassium atom reacts with an Example 3: A potassium atom reacts with an oxygen atom to form potassium oxide oxygen atom to form potassium oxide (K(K22O). O).

2 K + O 2 K + O K K22OO

O+

O -2+

K

K

K+1

K+1

Nomenclature of Binary Nomenclature of Binary Ionic CompoundsIonic Compounds

Roman numeral system. See Table 5.2 (Roman numeral system. See Table 5.2 (CFCTCFCT). ).

Rules: Rules: Names of the elements in order according to chemical Names of the elements in order according to chemical formula. formula.

Change the ending of the last element to “-ide”. Change the ending of the last element to “-ide”.

Consider ionic state of metal:Consider ionic state of metal:If the metal has only one ionic state, you are finished naming. If the metal has only one ionic state, you are finished naming.

If the metal has more than one ionic state, state in If the metal has more than one ionic state, state in parentheses after the metal the size of the charge on the parentheses after the metal the size of the charge on the metal ion. metal ion.

Nomenclature of Binary Ionic Nomenclature of Binary Ionic Compounds: Compounds: Formula to NameFormula to Name

ExamplesExamples: : 1.) LiCl1.) LiCl

LiLi+1+1 and Cl and Cl-1-1

lithium chlorine lithium chlorine lithium chlor lithium chlorideide

2.) CuO2.) CuO Copper oxygenCopper oxygenCuCu+2+2 and O and O-2-2 copper (II) oxygen copper (II) oxygen copper (II) ox copper (II) oxideide

Nomenclature of Binary Ionic Nomenclature of Binary Ionic Compounds: Compounds: Name to FormulaName to Formula

ExamplesExamples::1.) What is the chemical formula for sodium iodide. 1.) What is the chemical formula for sodium iodide.

Na and I Na and I NaNa+1+1 + I + I-1-1 NaI

2.) What is the chemical formula for potassium 2.) What is the chemical formula for potassium sulfide? sulfide?

K and S K and S KK+1+1 + S + S-2-2 Cross-over method: Cross-over method:

K2S

Name to FormulaName to Formula

ExamplesExamples: :

3.) Copper (II) oxide3.) Copper (II) oxide

CuCu+2+2 O O-2 -2 One One CuCu for one for one OO

CuCu22OO22 lowest-whole number ratios! lowest-whole number ratios!

CuO

4.) Iron (III) chloride4.) Iron (III) chloride

FeCl3

Covalent BondingCovalent Bonding

Electrons strongly shared, not transferred. Electrons strongly shared, not transferred.

Covalent bonds are weaker bond than Covalent bonds are weaker bond than ionic bonds; nonmetal bonded to ionic bonds; nonmetal bonded to nonmetal.nonmetal.

Examples:Examples:SOSO2 2 (sulfur dioxide)(sulfur dioxide)

HH22S (hydrogen sulfide)S (hydrogen sulfide)

NHNH33 (ammonia) (ammonia)

Types of Covalent BondsTypes of Covalent Bonds

Three major types of covalent bonds: Three major types of covalent bonds:

- Single: one pair of electrons- Single: one pair of electrons ExEx: C:H or C: C:H or C––H H

- Double: two pairs of electrons- Double: two pairs of electrons ExEx: C::O or C: C::O or C==OO

- Triple: three pairs of electrons- Triple: three pairs of electrons ExEx: N:::N or N: N:::N or N≡≡NN

Example: How many pairs of electrons are in the Example: How many pairs of electrons are in the hydrogen-oxygen bond in water?hydrogen-oxygen bond in water?

H-O-HH-O-H

Answer: 1 pairAnswer: 1 pair

Rules for Naming Rules for Naming Binary Covalent Compounds: Ex 1.Binary Covalent Compounds: Ex 1.

Start with the chemical formula: COStart with the chemical formula: CO22

Elements:Elements: carbon oxygencarbon oxygen First element-First element-

Use a prefix for elements Use a prefix for elements in quantity greater than one:in quantity greater than one:

carbon oxygencarbon oxygen Second element- Second element-

Use prefix for elements of any Use prefix for elements of any quantity:quantity:

carbon dioxygencarbon dioxygen Add Add –ide carbon dioxide

Nomenclature for Covalent Compounds: Name from Formula

Example 2Example 2: What is the chemical name for CO? : What is the chemical name for CO?

carbon monoxide.carbon monoxide.

Example 3Example 3: What is the chemical name for PCl: What is the chemical name for PCl33??

phosphorus trichloride. phosphorus trichloride.

Example 4Example 4: What is the chemical name for N: What is the chemical name for N22O?O?

dinitrogen monoxide. dinitrogen monoxide.

Nomenclature for Covalent Compounds: Formula from Name

Example 1Example 1: What is the chemical formula for : What is the chemical formula for dihydrogen monoxide?dihydrogen monoxide?

H2O

Example 2Example 2: What is the chemical formula for sulfur : What is the chemical formula for sulfur trioxide. trioxide.

SO3

Example 3Example 3: What is the chemical formula for : What is the chemical formula for tetraphosphorus trisulfide?tetraphosphorus trisulfide?

P4S3

ElectronegativityElectronegativity

The ability for a nucleus to attract The ability for a nucleus to attract electrons.electrons.

Atoms of different elements have Atoms of different elements have different abilities of attracting electrons. different abilities of attracting electrons.

See table in text, and lecture guide. See table in text, and lecture guide.

Applying Electronegativities: Applying Electronegativities: OverviewOverview

Take Take differences differences between the two between the two elements in a bond to determine elements in a bond to determine predominant character of bond. predominant character of bond. Nonpolar covalent bond: Nonpolar covalent bond: < 0.5. < 0.5. Polar covalent bond: Polar covalent bond: between 0.5 and 2.0. between 0.5 and 2.0. Ionic:Ionic: > 2.0. > 2.0.

Applying ElectronegativitiesApplying Electronegativities

ExamplesExamples: :

Hydrogen (HHydrogen (H22): H—H ): H—H

Difference = 0; nonpolar covalentDifference = 0; nonpolar covalentHydrogen chloride (HCl): H—ClHydrogen chloride (HCl): H—Cl

Difference = 0.96; polar covalentDifference = 0.96; polar covalentSodium chloride (NaCl): Sodium chloride (NaCl):

Difference = 2.23; ionic Difference = 2.23; ionic Na Na+1+1 Cl Cl-1-1


Examples: How is the electron density Examples: How is the electron density around the molecule distributed for a around the molecule distributed for a hydrogen molecule?hydrogen molecule?

Hydrogen atoms Hydrogen atoms hydrogen hydrogen moleculemolecule

H – H H + H


ExampleExample: Give the partial charges on the : Give the partial charges on the atoms in the hydrogen-chlorine bond in atoms in the hydrogen-chlorine bond in HCl. Show the dipole moment in the HCl. Show the dipole moment in the bond. bond.

δδ+ + δδ--

H – ClH – Cl

2.2 3.162.2 3.16 H – Cl

How is the electron

density distributed?


Example: Show ions given their Example: Show ions given their electronegativities. electronegativities.

Na ClNa Cl

0.93 3.160.93 3.16

NaNa+1+1 Cl Cl-1-1

Polyatomic moleculesPolyatomic molecules

See See LGLG (p. 169) for rules on preparing (p. 169) for rules on preparing molecules.molecules.

Go through examples in the Lewis-Dot Go through examples in the Lewis-Dot Structures Worksheet for Covalent Structures Worksheet for Covalent Molecules in the Molecules in the LGLG (p. 171-175) (p. 171-175)

Consult rules for writing Lewis-dot Consult rules for writing Lewis-dot structures as reference. structures as reference.

Polyatomic IonsPolyatomic Ions

Polyatomic ions: ions that contain more than one atom.

CFCT: Table 5.4 on p. 235. Be familiar with these ions. Examples include:

Carbonate (CO3-2)

Bicarbonate (HCO3-1)

Phosphate (PO4-3)

Sulfate (SO4-2)

Hydroxide (OH-1)Nitrate (NO3

-1)Ammonium (NH4

+1)

Writing Lewis-dot StructuresWriting Lewis-dot Structures

See Rules for “Writing Lewis-Dot See Rules for “Writing Lewis-Dot Structures” (p. 203 in Lecture Guide). Structures” (p. 203 in Lecture Guide).

Determining the Central Atom in Determining the Central Atom in Lewis-Dot Structures of MoleculesLewis-Dot Structures of Molecules

Consider how many free pairs of electrons an atom has Consider how many free pairs of electrons an atom has before bonding. The higher this number, the more potential before bonding. The higher this number, the more potential for bonding. This means it is more likely to be a central atom. for bonding. This means it is more likely to be a central atom.

Abridged Periodic Table of Elements – Lewis Dot Structures

1A 2A 3A 4A 5A 6A 7A 8A

H He

Li Be B C O F Ne

Na Mg Al Si P S Cl Ar

N

Free RadicalsFree Radicals

Molecules/atoms with an unpaired Molecules/atoms with an unpaired electron. electron.

Importance in terms of health: Can cause Importance in terms of health: Can cause damage to tissue in the body. damage to tissue in the body.

Antioxidants are used to counteract free Antioxidants are used to counteract free radicals: Sources include blueberries and radicals: Sources include blueberries and green tea. green tea.

Cl N O

Types of Molecular GeometriesTypes of Molecular Geometries

Polar vs. Nonpolar MoleculesPolar vs. Nonpolar Molecules

Dipole: a molecule that has Dipole: a molecule that has unequally distributed charges. unequally distributed charges.

Polar- having unequally distributed charge.Polar- having unequally distributed charge. Nonpolar- having equally distributed charge. Nonpolar- having equally distributed charge.

H Clδ+ δ-

H Clδ+ δ-

Polar Example: Hydrogen Chloride

WaterWater: Notice how the : Notice how the electron pairs spread electron pairs spread out and cause a bent out and cause a bent geometry. This also geometry. This also causes the formation causes the formation of a dipole, making of a dipole, making water polar. water polar.

Water as a Polar MoleculeWater as a Polar Molecule

H H

O

Molecular Geometry: Bent


Bond Dipole moment


δ-

δ+δ+

H H

O


Overall Dipole Moment = Polar


δ-

δ+δ+

H H

O

Ammonia (NHAmmonia (NH33)): Notice : Notice how the electron how the electron pairs spread out and pairs spread out and cause a pyramidal cause a pyramidal geometry. This also geometry. This also causes the formation causes the formation of a dipole, making of a dipole, making ammonia polar. ammonia polar.

Ammonia as a Polar MoleculeAmmonia as a Polar Molecule

H H

N

H

Molecular Geometry: Pyramidal


H H

N

H

δ-

δ+

δ+

δ+



H H

N

H


δ-

δ+

δ+

δ+

Overall Dipole Moment = Polar

Methane (CHMethane (CH44)): Notice : Notice how the electron pairs how the electron pairs spread out and cause a spread out and cause a tetrahedral geometry. tetrahedral geometry. This causes the This causes the molecule to be nonpolar molecule to be nonpolar since the overall dipole since the overall dipole moments (see +moments (see +) to ) to counteract each other. counteract each other.

Methane as a Nonpolar Methane as a Nonpolar MoleculeMolecule

H H

CH

H

Molecular Geometry: Tetrahedral

δ+

δ+

δ+

δ+

δ-

Methane as a Nonpolar Methane as a Nonpolar MoleculeMolecule

H H

CH

H

Molecular Geometry: Tetrahedral

No Dipole Moment = Nonpolar!No positive or negative side overall

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Ch04 lecpptchem1012011f