how it will be decided that how many electrons will be shared in a covalent bond ? is there any calculation to find the number of electrons in bond sharing ? please draw the lewis dot structure of S8 .thank you.

Every atom has a tendency to acquire the noble gas configuration,and this is the reason why atoms participates in bonding?During bonding,like in covalent one where shairing of electrons takes place,number of valence electrons present in oitermost shell will decide the no. of electrons that will shaired during bond formation.Generally non-metals which have 4,5,6,or 7 valence electrons will undergo covalent bonding by shairing 4,3,2 and 1e- respectively. For e.g-
in Cl2 molecule each Cl atom has 7e- (Cl = 17 = 2,8,7).On observing the configuration it is clear that if it either share 1e- or donate 7e- of outermost shell it will become noble gas.But donationg 7e- is quite difficult instead of shairing 1e-.So both Cl-atoms shaire 1e- each and formed chlorine molecule and aquire noble gas configuration like Ar.Similarly in case of O2 molecule,shairing of 2e-s by each O-atom takes place as both have O = 8(2,6) 6e-,so on shairing 2e-s both aquire noble gas configuration like Ne.