Chapter 6 and 7Chapter 6 and 7

Chemical bondingChemical bonding

12.1 Types of Chemical 12.1 Types of Chemical BondsBonds

Bonds: a force that holds groups of Bonds: a force that holds groups of two or more atoms together and two or more atoms together and makes them function as a unitmakes them function as a unit Required 2 e- to make a bondRequired 2 e- to make a bond

Bond energy: amount of energy Bond energy: amount of energy required to form or to break the required to form or to break the bondbond

Ionic BondingIonic Bonding

Occurs in ionic Occurs in ionic compoundcompound

Results from Results from transferring transferring electronelectron

Created a strong Created a strong attraction among attraction among the closely pack the closely pack compoundcompound

Electron AffinityElectron Affinity

Electron Affinity (Eea): The energy released when a neutral atom gains an electron to form an anion

Covalent BondingCovalent Bonding

Formation of a covalent BondFormation of a covalent Bond Two atoms come close together, and electrostatic Two atoms come close together, and electrostatic

interactions begin to developinteractions begin to develop Two nuclei repel each other; electrons repel each otherTwo nuclei repel each other; electrons repel each other Each nucleus attracts to electrons; electrons attract both Each nucleus attracts to electrons; electrons attract both

nucleinuclei Attractive forces > repulsive forces; then covalent Attractive forces > repulsive forces; then covalent

bond is formedbond is formed

12.2 Electronegativity12.2 Electronegativity Electronegativity Electronegativity

(EN):(EN): the ability of the ability of an atom in a an atom in a molecule to attract molecule to attract the shared electron the shared electron in a bondin a bond

Metallic elements – Metallic elements – low low electronegativitieselectronegativities

Halogens and other Halogens and other elements in upper elements in upper right-hand corner of right-hand corner of periodic table – high periodic table – high electronegativityelectronegativity

PolarityPolarity Polar covalent bondsPolar covalent bonds

– the bonding electrons – the bonding electrons are attracted somewhat are attracted somewhat more strongly by one more strongly by one atom in a bondatom in a bond Electrons are not Electrons are not

completely transferredcompletely transferred More electronegative More electronegative

atom: δ- . (δ represents atom: δ- . (δ represents the partial negative the partial negative charge formed)charge formed)

Less electronegative Less electronegative atom: δ+atom: δ+

Relationship Between Relationship Between Electronegativity and Bond Electronegativity and Bond

TypeType Predicting bond polarityPredicting bond polarity

Atoms with similar electronegativity Atoms with similar electronegativity (Δ EN <0.4) –form nonpolar bond(Δ EN <0.4) –form nonpolar bond

Atoms whose electronegativity differ Atoms whose electronegativity differ by more than two (Δ EN > 2) – form by more than two (Δ EN > 2) – form ionic bondsionic bonds

Atoms whose electronegativity differ Atoms whose electronegativity differ by less than two (Δ EN < 2) – form by less than two (Δ EN < 2) – form polar covalent bondspolar covalent bonds

PolarityPolarity

ExamplesExamples

For each of the following pairs of For each of the following pairs of bonds, choose the bond that will be bonds, choose the bond that will be more polarmore polara.a. H-P, H-CH-P, H-C b.b. N-O, S-ON-O, S-O

12.312.3 Polarity and Polarity and Dipole MomentDipole Moment

Dipole moment:Dipole moment: a vector quantity a vector quantity

from the center of from the center of the positive charge the positive charge to the center of to the center of negative chargenegative charge

Represents with an Represents with an arrowarrow

E.g Draw the dipole E.g Draw the dipole moment for HF, moment for HF, HH22O, HCl, OFO, HCl, OF

13.413.4 Stable Electron Stable Electron Configurations and Charges Configurations and Charges

on Ionson Ions Atoms in stable compounds almost Atoms in stable compounds almost

always have a noble gas electron always have a noble gas electron configurationconfiguration

Predicting Formulas of Ionic Predicting Formulas of Ionic CompoundCompound

Electrons lost by a metal come from Electrons lost by a metal come from the highest-energy occupied orbitalthe highest-energy occupied orbital

Electrons gained by a nonmetal go Electrons gained by a nonmetal go into lowest-energy unoccupied orbitalinto lowest-energy unoccupied orbital

Ions configurationIons configuration

ExamplesExamples

Predicting formulas of Ionic Predicting formulas of Ionic compound by showing how they compound by showing how they loses or gains electronsloses or gains electrons

Ca and OCa and O Sr and ClSr and Cl

12.5 Ionic Compound12.5 Ionic Compound

Lattice energy Lattice energy (U)(U) – the sum of – the sum of the electrostatic the electrostatic interaction interaction energies between energies between ions in a solidions in a solid

Refer to the Refer to the breakup of a breakup of a crystal into crystal into individual ionsindividual ions

12.6 Lewis Structures12.6 Lewis Structures

represents how an atom’s valence represents how an atom’s valence electrons are distributed in a electrons are distributed in a molecule molecule

Show the bonding involves (the Show the bonding involves (the maximum bonds can be made)maximum bonds can be made)

Try to achieve the noble gas Try to achieve the noble gas configurationconfiguration

RulesRules Duet Rule: sharing of 2 electronsDuet Rule: sharing of 2 electrons

E.g HE.g H22 H H :: H H

Octet Rule: sharing of 8 electronsOctet Rule: sharing of 8 electrons Carbon, oxygen, nitrogen and fluorine always Carbon, oxygen, nitrogen and fluorine always

obey this rule in a stable moleculeobey this rule in a stable molecule E.g FE.g F22, O, O22

Bonding pair:Bonding pair: two of which are shared two of which are shared with other atomswith other atoms

Lone pair or nonbonding pair:Lone pair or nonbonding pair: those those that are not used for bondingthat are not used for bonding

12.7 Lewis Structures of 12.7 Lewis Structures of Molecules with Multiple Molecules with Multiple

BondsBonds Recall: Elements typically obey the octet Recall: Elements typically obey the octet

rule; they are surrounded by eight electronsrule; they are surrounded by eight electrons single bond: involves two atoms sharing single bond: involves two atoms sharing

one electronone electron Double bond: involves two atoms sharing Double bond: involves two atoms sharing

two pair of electronstwo pair of electrons Triple bond: involves two atoms sharing 3 Triple bond: involves two atoms sharing 3

pair of electronspair of electrons Use 6N + 2 RuleUse 6N + 2 Rule

N = number of atoms other than HydrogenN = number of atoms other than Hydrogen

Dots Lewis StructureDots Lewis Structure

If If Total valence – (6N + 2) = 2 Total valence – (6N + 2) = 2

1 double bond1 double bond

Total valance e- - (6N + 2) = 4Total valance e- - (6N + 2) = 4 two double bonds or 1 triple bondtwo double bonds or 1 triple bond

Rules for Wring Dot Lewis Rules for Wring Dot Lewis structurestructure

Draw a dot Lewis structure of ClODraw a dot Lewis structure of ClO44--

Calculate the total number of valence Calculate the total number of valence electrons of all atoms in the moleculeelectrons of all atoms in the molecule

Cl – Valence e- = 7Cl – Valence e- = 7 O – Valence e - = 6 x 4 = 24e-O – Valence e - = 6 x 4 = 24e- ClOClO44

-- => total valence e- = 7 + 24 +1 ( -1 => total valence e- = 7 + 24 +1 ( -1 charge) = 32 e-charge) = 32 e-

O

O

O Cl O

O

O

O

Cl

O

RulesRules

Create a skeletal structure using the Create a skeletal structure using the following rules:following rules: a.Hydrogen atoms (if present) are always on the a.Hydrogen atoms (if present) are always on the

“outside” of the structure. They form only one bond“outside” of the structure. They form only one bond b.The central atom is usually b.The central atom is usually least electronegativeleast electronegative. It . It

is also often unique (i.e,. the only one atom of the is also often unique (i.e,. the only one atom of the element in the molecule). Remember, there might be no element in the molecule). Remember, there might be no “central” atom.“central” atom.

c.Connect bonded atoms by line (2-electron, covalent c.Connect bonded atoms by line (2-electron, covalent bondsbonds

O

O

O Cl O

O

O

O

Cl

O

O

O

O Cl O

O

O

O

Cl

O

O

O

O Cl O

O

O

O

Cl

O

O

O

O Cl O

O

O

O

Cl

O

RulesRules

Place lone pairs around outer atoms Place lone pairs around outer atoms (except hydrogen) so that each atom (except hydrogen) so that each atom has an octethas an octet

Cl OO

O

O

RulesRules

Calculate the number of electrons you Calculate the number of electrons you haven’t usedhaven’t used. Subtract the number of . Subtract the number of electrons used so far, including electrons used so far, including electrons in lone pair and bonding electrons in lone pair and bonding pairs, from the total in Step 1. Assign pairs, from the total in Step 1. Assign any remaining electrons to the central any remaining electrons to the central atom as lone pairatom as lone pair

Cl-O bonds = 4 x 2e- = 8 e-Cl-O bonds = 4 x 2e- = 8 e- O – 4 x 6e- = 24 e-O – 4 x 6e- = 24 e- Total used = 8 + 24 = 32 e-Total used = 8 + 24 = 32 e-

RulesRules

If the central atom is B (boron) or Be If the central atom is B (boron) or Be (beryllium), skip this step(beryllium), skip this step

If the central atom has an octet after If the central atom has an octet after step 4, skip this stepstep 4, skip this step If the central atom has only 6 electrons, move a If the central atom has only 6 electrons, move a

lone pair from an outer atom to form a double lone pair from an outer atom to form a double bond between outer atom and the central atombond between outer atom and the central atom

If the central atom has only 4 electrons, do If the central atom has only 4 electrons, do Step 5a to two different outer atoms (i.e, form Step 5a to two different outer atoms (i.e, form two double bonds) or twice to one outer atom two double bonds) or twice to one outer atom (i.e., form one triple bond)(i.e., form one triple bond)

ExamplesExamples

Give the Lewis structure for the Give the Lewis structure for the followingfollowing NaNa OO HH22OO NHNH44

++

CFCF44,, BeFBeF22

CO2 CO2 NONO33--, ,