Chapter 7Chapter 7

Chemical BondsChemical Bonds

Chemical bondChemical bond

Link between atoms Link between atoms that results from that results from attractions of their attractions of their nuclei for enuclei for e--

1. Ionic bond1. Ionic bond

Attraction between (+) and (-) ions, Attraction between (+) and (-) ions, exchange of eexchange of e- -

Usually between metals and nonmetalsUsually between metals and nonmetals

IonIon

Atom or group of atoms with a (+) or (-) Atom or group of atoms with a (+) or (-) chargecharge

Cation: (+) chgCation: (+) chg Anion: (-) chgAnion: (-) chg

e.g. sodiume.g. sodium

e.g. chlorinee.g. chlorine

Na and Cl ions Na and Cl ions ionic bond ionic bond

Polyatomic ionsPolyatomic ions

Charged group of bonded atomsCharged group of bonded atoms e.g. phosphate ion e.g. phosphate ion (PO(PO44

3-3-))

2. Covalent bonds2. Covalent bonds

Sharing of eSharing of e--

Usually betweenUsually between

nonmetals nonmetals

Covalent bondingCovalent bonding

Molecule- smallest unit quantity of matter Molecule- smallest unit quantity of matter that can exist by itself, e.g. atom of He, that can exist by itself, e.g. atom of He, OO22, H, H22OO

Diatomic molecule-2 atoms, e.g. HCl, HDiatomic molecule-2 atoms, e.g. HCl, H22

e.g. hydrogen moleculee.g. hydrogen molecule

Bond typesBond types

Chemical bonds are usually not Chemical bonds are usually not completely ionic completely ionic oror covalent covalent

4.0 1.7 0.3 0.0

ionicPolar covalent

Non polar covalent

Difference in electronegativity

electronegativityelectronegativity

Measure of ability of an atom in a chem. Measure of ability of an atom in a chem. cmpd. to attract electronscmpd. to attract electrons

Chemical formulaChemical formula

Type and relative # of atoms in a Type and relative # of atoms in a chemical compound, e.g. Hchemical compound, e.g. H22OO

ee-- config. config.andandbondingbonding

Octet ruleOctet rule

Atoms often gain, lose, or share electrons to Atoms often gain, lose, or share electrons to achieve the same number of electrons as the noble achieve the same number of electrons as the noble gas closest to them in the periodic tablegas closest to them in the periodic table

Because all noble gasses (except He) have filled Because all noble gasses (except He) have filled ss and and pp valence orbitals (8 electrons), many atoms valence orbitals (8 electrons), many atoms undergoing reactions also end up with 8 valence undergoing reactions also end up with 8 valence electrons. electrons.

Octet RuleOctet Rule: : Atoms tend to lose, gain, or share Atoms tend to lose, gain, or share electrons until they are surrounded by 8 valence electrons until they are surrounded by 8 valence electronselectrons

Note: there are exceptions to the octet rule, e.g.He Note: there are exceptions to the octet rule, e.g.He

Valence electronsValence electrons

Electrons lost, gained, or shared in Electrons lost, gained, or shared in formation of chemical cmpds.formation of chemical cmpds.

Lewis structuresLewis structures

NN2 2 (nitrogen)(nitrogen)

Carbon tetrachlorideCarbon tetrachloride

Lewis structureLewis structure

Structural formulaStructural formula

Structural formulaStructural formula

Indicates the kind, number, arrangement, Indicates the kind, number, arrangement, and bonds of atoms in moleculesand bonds of atoms in molecules

Single bondsSingle bonds

Sharing (1) pr. of eSharing (1) pr. of e--

Double bondDouble bond

Sharing (2) pr. of eSharing (2) pr. of e--

Triple bondTriple bond

Sharing (3) pr of eSharing (3) pr of e--

3. Metallic bonds3. Metallic bonds

Metal-metal bonds, electron ‘sea’Metal-metal bonds, electron ‘sea’

Metallic bondingMetallic bonding

Results from attraction between (+) ions Results from attraction between (+) ions and surrounding mobile electrons and surrounding mobile electrons (electron sea)(electron sea)

Motion of free electrons accounts for Motion of free electrons accounts for high high conductivity of heat and electricityconductivity of heat and electricity

Malleability and ducticity possible Malleability and ducticity possible because bonding is not directionalbecause bonding is not directional

4. Hydrogen bonds4. Hydrogen bonds

Weak bonds Weak bonds betweenbetween molecules due to molecules due to partialpartial charges on atoms charges on atoms

e.g. watere.g. water

Polarity of water Polarity of water molecule molecule hydrogen hydrogen bondingbonding

Review: ionic or Review: ionic or covalent?covalent?

Ca and ClCa and Cl IonicIonic Na and FNa and F IonicIonic N and ON and O CovalentCovalent H and HH and H CovalentCovalent

Review: Lewis StructureReview: Lewis Structure

1.1. H + H + OH + H + O

2.2. CC22HH4 4 (ethene)(ethene)

What kind of bondWhat kind of bondss??

Define:Define:

Covalent bondCovalent bond Ionic bondIonic bond Metallic bondMetallic bond Hydrogen bondHydrogen bond Diatomic moleculeDiatomic molecule CationCation AnionAnion ElectronegativityElectronegativity