Āris Kaksis 2018 Year, Riga Stradin`s University:

Chemical interaction forcesandcovalent bond

Interaction forces between atoms, ions and molecules are absent just in gas state of substances. Ifcool gasesenoughits becomes liquid and freeze solid, because between atoms, ionsand molecules are formingchemical interactions forces, due to interaction forcesparticles stick together and aggregates.

Chemical interaction are attraction and binding forces, whatworks between atoms, ionsand molecules, formingcompounds, aggregatesand complexes. In nature it can observe as atoms, moleculesandionsattractsandstick together, for example: water vapors (gas water moleculesH2O) forms rein drops, snowflakes , fog and clouds, whichmerge and precipitategetting into puddles, lakes, rivers, sees, oceans, glaciers and snow coats. Chemical binding forcesaccording its strength are classified as weak chemical interaction forces, as moderate chemical interaction forces andas strong chemical interaction forces, where strong interaction forces are calledaschemical bond. Chemical bond establishes between two atomsaccordingexchange mechanismor donor-acceptor mechanism.

1.Exchange mechanismbinds two atomswith common binding electron pair orbital , what has the namecovalentbond.That forms commonly for two atoms, if one atomon outer electronshell energy levelhassingleunshared electronwith spin +1/2and, if second atom on outer electron shell energy level has single unshared electron withopposite spin -1/2. That bindschemical bond members, atoms firm togetherwithsingle valuechemicalcovalentbond between atoms. From primary school is known, that covalentbondto each of two atomsmakein chemical compoundonevalence value. Totalvalencenumber for chemical element atomin compounddetermines this atom made number of covalentbonds.

2. Donor acceptor mechanismbinds two atoms with common binding electron pair orbital , what has the namedonor-acceptorbondorcoordinativebond. That forms commonly for two atoms, if onecentralatomon outer electron shell energy level has empty orbital , and, if second atom on outer electron shell energy level hasat least oneunshared electron pair orbital. Central metal elementatomusually iscation withemptyseveral orbitals, in which atomacceptorcoordinatesarounditselfone, two, fouror six atoms, whichare electron pairdonors, andthosecallasligands.In coordinative compoundcentral atomhascoordinationnumber, whichcorresponds todonor-acceptorbondnumber, donor atomaccountandligandsnumber, whichcoordinates aroundcentral atom.

VSEPR ValentShellElectronPairRepulsionaccordingExchange Mechanism.

Chemical bond between two atoms makescommon electron pair, whatcallascovalentbond.

Covalent – coinLatin – common, withand – valēreinLatin – to bevaluable.

Chemical interaction problem, binding withcovalentbondorany otherchemicalinteraction bond isscience central problem.

I , II , III Covalent bond types in chemistry and examples

ICovalentnonpolar, polar,ionicbond: nonmetals, oxides, acids, bases, salts, minerals, organic compounds;
II Donor-acceptorbondsor coordinativebonds:complex orcoordinative compounds and
III. Metallicbondin metals are for sorbitalelectrons which havesavedfree, sphericalground wavestate in body of metalsand as the free electrons in metals assign for itsmetallic properties : reflect the light as mirror, conductivity etc. as for example: Al, Fe, Cu, Ag, Au, Pt etc..

Different in nonmetalp, dandforbitals electrons arelocalizedatnode planesandcan not befreeon positivecharged atomnuclei, which site is localized on node plane, as itis obviouslyobserving oppositeto freeelectrons ons orbitalelectrons in metallicbody, which do not have node planesand as well as are in metallic body free electrons,
as well as electronss are independent on atomic nucleibecause of node planeabsence and
as well as belong to all atoms of metallic bodyinstantly.

Exchange mechanism - , covalent bonds.

Valent Shell Electron Pair Repulsion (VSEPR)accordingexchange mechanism definefife points, whatreveal covalent bond properties to form nonpolar, polar and ionic covalent bonds, which have the compounds
nonmetals, oxides, acids, bases, salts, minerals and organic compounds

1.Covalentbondbind both atomswith common electron pair having opposite spins.

1. atoms 2. atoms

  

2. Electron pairestablishoverlapping both orbitals. If stronger is overlapping, then stronger iscovalentbond.

Hydrogen1s orbitaland fluorine2p orbitaloverlapping between atomsmakecommon electron pair orbital – covalentbond (1.figure)

 node plane  of fluorine atom

 designation ofchemical formula using different types:

H + F  H-F Structural formula Electron formula Molecular formula

H + F HF HF HF

1.Figure. Covalent bondformationbetweenHandF atomsoverlapping electron orbitals. Common electron pairof both atomsvalent electron adding+ withopposite spins.

3. Orbitaloverlapping zonebetween positivecharged(+)nucleusincreased electron negativecharge() densityweakenrepulsingforcesbetween atomsandstrengtheningcovalentbond.

node planes   of chlorine atoms

designation of chemical formula using different types:

ClCl Structural formula Electron formula Molecular formula

Cl+e–e–Cl+  Cl—Cl chlorine moleculeCl2

2.Figure. Electron negative()charge densitybetweenpositive charged(+)nucleusweakenrepulsingforcesandstrengtheningcovalentbond.

4.Covalentbond issaturated, becausecommon orbital of both atoms mayoccupyjusttwo electronswithanti-parallel spins. Any chemical element atom valencein compound is univalent and corresponds to onecommon orbitalwith two electrons. Hydrogen in compounds isunivalentH-H (H:H hydrogen moleculeH2), H—O—Hin water moleculeH2Ohydrogen isunivalent.Oxygen—O— istwo valentwithtwovalences – each of twocovalentbonds issaturatedHOH having valence onewhole.

5.Covalentbondhas central atomsymmetricgeometryin space, whatoptimize maximal overlapping orbitalsalongchemicalbondbetween atoms. Atomsbind to form centralsymmetricgeometric figures, whichforming with valenceangle and bond length (distance between atoms).

Molecular orbitals (covalentbonds) areforming two possibletypes of orbitaloverlappingconfiguration sigma (singular) bonds, which apply symmetrisation around central atom,

and pi  (paired)bonds.

3.fig. F-F bondforms p orbitalswhich symmetry axesalignonone line. Orbitalsapproacheswith electron antiparallel spinsand fuse inredregion, blueregionsremainoutsidebehind atomnuclei. Nodes planes retain positionon atomnuclei perpendicular to symmetry axesand arecorrelated parallel each to other.

  nodes planes   of fluorine atoms

 designation of chemical formula using different types:

F + F  FF Structural formula Electron formula Molecular formula

F + F  FF fluorine molecule F2

3.Figure. F and F atomic p orbitalsfuse into molecular orbitaland form electron negativecharge() densitybetween fluorine positivecharged atomnucleiweakenedrepulsion forcesandstrengthening covalent bondin fluorine moleculeF2. Atomicnucleilieson parallel orbitalnode plans perpendicular symmetryaxisline, whichdivide negativechargedelectron() densityinto three symmetric regions andgreatest electrondensityliesbetween atomicnuclei.



C + C  CC  >C=C< double bond with  and  bonds

C + C CC

4.Figure. C and C atomicorbitals fuse into  molecular orbital andform in double bondC=C<secondbondafter sigma bondCCformation. On common node plane lie both carbon atomic nuclei, but negative charge () density betweenpositive charged atom nuclei weakened repulsion forces and strengthening covalent bond togetherwith sigma bondon formed double bondC=C< .

bondforms overlapping (CandCorOorSorPorN) atomic electron orbitalswith parallel symmetryaxis. Atomicnucleiapproachoncommonnode planeand fuse p orbital partson both sideof node plane.

 molecular orbital electron negativechargedensityincreasesonline, whatconnect atomicnuclei. bondformsnegative charge densityincreasebetween atoms(C and C or Oor Sor P or N)both sidenode planes. Latinword singulāris –one, alone in EnglishandGreeksletter sigma  isfirst letterof word anddesignatesimplecovalentbond – sigma bond. Doublebond is paired bondC=C< andLatin wordpār –pair in Englishwhich firstletter fromGreeks alphabet is pi which designate doubleor triple bond pi.

 orbitalparallel to orbital- sigmacovalentbond in ethane () in etheneand ethyne (H-CC-H) as additional to  bond (singular bond) aredoubleand triple bonds. Naturallyoccurringbondexistonly incombinationwithbondasadditionalcovalentbond into doubleand triplebonds.

C=O ; O=C=O ;

Carbon(II) oxide; carbon(IV) oxide; carbonic acidH2CO3

Simplecovalent bonds alwaysare molecular orbitals, but double () and triple (H-CC-H) bonds are molecular orbital (oneortwo) additionalcombinationwithsimple covalentbond molecular orbital. Triple bondforboth orbitalsnode planesareinterconnected perpendicular.

With  bond connected atoms in moleculehas rotationfreedomdimensionaroundsymmetry axis of orbital.

Acetic acid moleculeHOOC-CH3betweencarbon atomshas sigma bond.

However doublebondissolid,steadyand consistent (consistere – Latinword – solid, firm, standing).

ethene molecule is planarinflexible structurewithout rotationaroundC=C< doublebond.
Ethynetriplebondprovidesfour atomsquiteon linear structure H-CC-H straight stick form.

Exercise. Draw the structure formulas for given molecules! Account sigma andbonds? Accountandshowbondsbetween which atomsin moleculeareformed? OxygenO2, nitrogenN2, carbon(IV) oxideCO2, sulfur(IV) oxideSO2, sulfur(VI) oxide SO3, nitrogen(IV) oxideNO2, carbonic acidH2CO3,
sulfuric acidH2SO4, phosphoric acidH3PO4, acetic acidCH3COOH, acetoneCH3COCH3,
calcium carbideCaC2, ethyneC2H2.

Most importantfor covalent bond

1. Covalentbondbetween two atomsformscommon electron pairin molecular orbital.

2. According exchange mechanismfrom eachatom participateunpairedfree electronand , formingcommon orbitalwith electron pairhavingopposite spins .

3. Sigma bond issimple singlecovalentbond, whichcan getadditionalbonds doubleor triplebonds.

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