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Chemical BondingChemical BondingPresented by:Presented by:Gulfam HussainGulfam Hussain
Chemical BondingChemical Bonding►Chemical compounds are formed by theChemical compounds are formed by thejoining of two or more atoms.joining of two or more atoms.►►A stable compound occurs when the totalA stable compound occurs when the totalenergy of the combination has lower energyenergy of the combination has lower energythan the separated atoms.than the separated atoms.
The two extreme cases of chemicalThe two extreme cases of chemicalbonds are:bonds are: Covalent bond: bond inCovalent bond: bond inwhich one or more pairs ofwhich one or more pairs ofelectrons are shared by twoelectrons are shared by twoatoms.atoms. Ionic bond: bond in whichIonic bond: bond in whichone or more electrons fromone or more electrons fromone atom are removed andone atom are removed andattached to another atom.attached to another atom.
Other Types of Bonds Metallic Bonds:In metals all atoms loses their valenceelectrons which form electronic cloud , whichattracts the nucleus of neighboring atoms. Hydrogen Bonding:Electrostatic force of attraction between highlyelectronegative atom and partially positivehydrogen atom e.g water.
Ionic Bond An ionic bond is a type of chemical bond formed through an electrostatic attraction between two oppositely charged ions. Ionic bonds are formed between a cat ion, which is usually a metal, and an anion, which is usually a nonmetal. Example: NaCl forms ionic bond.
How are Ionic Bonds Formed?How are Ionic Bonds Formed? Elements from opposite ends of theElements from opposite ends of theperiodic table will generally form ionicperiodic table will generally form ionicbonds.bonds.
Properties of Ionic CompoundsProperties of Ionic Compounds Crystalline solidsCrystalline solids High melting and boiling pointsHigh melting and boiling points Conduct electricity when meltedConduct electricity when melted Many soluble in water but not in nonpolarMany soluble in water but not in nonpolarliquidliquid
Covalent BondsCovalent Bondsbond in which one or more pairs ofbond in which one or more pairs ofelectrons are shared by two atoms.electrons are shared by two atoms.The atoms in covalent bonds do notThe atoms in covalent bonds do notlose or gain electrons, insteadlose or gain electrons, insteadThey share pairs of electrons toThey share pairs of electrons toachieve stability, often by fillingachieve stability, often by fillingtheir outer energy levels totheir outer energy levels toachieve an octet.achieve an octet.Example: N2 forms covalent bond.Example: N2 forms covalent bond.
How are Covalent Bonds Formed? Elements which are close together inelectronegativity tend to form covalent bondsand can exist as stable free molecules. Carbon dioxide is a common example.
First Subtype of CovalentFirst Subtype of CovalentBondingBonding Nonpolar bondNonpolar bond Example: HExample: H2 Because both atoms in the HBecause both atoms in the H2 moleculemoleculehave an equal attraction (or affinity) forhave an equal attraction (or affinity) forelectrons, the bonding electrons areelectrons, the bonding electrons areequally shared by the two atoms, and aequally shared by the two atoms, and anonpolar covalent bond is formed.nonpolar covalent bond is formed.
Second Subtype of CovalentSecond Subtype of CovalentBondingBonding• Polar Bond• formed when electrons are unequallyshared between two atoms• Example: the hydrogen-oxygen bond inthe water molecule.
Properties of CovalentProperties of CovalentCompoundsCompounds• Gases, liquids, or solids• Low melting and boiling points• Poor electrical conductors in all phases• Many soluble in non polar liquids but not inwater• Are brittle• When 2 atoms bond covalently theresulting particle is a molecule
Coordinate CovalentCoordinate CovalentBondsBonds Covalent bonds in which both of the electronsCovalent bonds in which both of the electronsin the shared pair come from the same atomin the shared pair come from the same atom Covalent bonds don’t lose or gain electronsCovalent bonds don’t lose or gain electrons Electrons are not shared equallyElectrons are not shared equallyExample:Example:The bond between NH3 and BF3 isThe bond between NH3 and BF3 is CoordinateCoordinateCovalent BondsCovalent Bonds
What Have You Learned?What Have You Learned? What are the two extreme casesWhat are the two extreme casesof bonds?of bonds? Do covalent bonds lose or gainDo covalent bonds lose or gainelectrons? (Yes or No).electrons? (Yes or No). Why do atoms bond?Why do atoms bond?