Reactivity The reactivities of the alkali metals increase going down the group. This is the result of a combination of two factors: the first ionisation energies and atomisation energies of the alkali metals. Because the first ionisation energy of the alkali metals decreases down the group, it is easier for the outermost electron to be removed from the atom and participate in chemical reactions, thus increasing reactivity down the group. The atomisation energy measures the strength of the metallic bond of an element, which falls down the group as the atoms increase in radius and thus the metallic bond must increase in length, making the delocalised electrons further away from the attraction of the nuclei of the heavier alkali metals. Adding the atomisation and first ionisation energies gives a quantity closely related to (but not equal to) the activation energy of the reaction of an alkali metal with another substance. This quantity decreases going down the group, and so does the activation energy; thus, chemical reactions can occur faster and the reactivity increases down the group.
reactivItY THe ReacTivities of tHe alkaLi mETAls InCReaSE going down the groUP. this is The result of a comBinaTIoN of twO factors: tHe FiRsT ionisATIoN enE.rgiEs AND atOmIsAtIon EnERgies of thE alKali mEtalS. beCAuSE tHE FirsT ionIsAtIOn eNeRgy oF the aLkali mETals deCrEasES dOwN the gRouP, It iS Easier FOr tHe outermoSt eLECtroN to bE remoVeD FroM the aToM and paRtiCipAte iN ChemicaL reacTions, thUs incREASinG REaCTIvity down the Group. ThE ATOMiSAtioN Energy measURes thE StReNgTh OF tHE metAllic bOnd of an ELEmeNT, WHiCh falLs down The GrOUp as The atOms increase in radiUS ANd tHus the mEtALLIc BoNd Must increAse In LenGth, mAking tHE dElocalised EleCtronS FuRthEr AWAy frOm thE attracTIoN of THE nuclei oF tHE HeAvier alkalI metals. addinG thE aTomiSation and fiRst ionisatiOn eNergies gIveS A QUantIty cLosely related To (but Not Equal To) ?tHE aCTivAtion energy of tHe rEAction of aN alkALI Metal with aNother SubsTaNCE. THIs QuaNtiTY decReAsEs going dOwn The grOup, aND sO doeS the aCTiVation enErgy; tHUs, cHemICal reactioNs cAn OCcur Faster and The reACTiviTy increasEs dOwn thE gROuP.