How do i determine valence shells and the no. of valence electrons of an atom?

for example, lithium.

How do i determine valence shells and the no. of valence electrons of an atom?
the valency is the nomber of electrons gained , lost or shared by one atom to form a molecule with other atoms.



monovalent : ex. hydrogen atom ( 1H ) the hydrogen atom contains one electron , so it can gain or share by one electron to complete the "k" level

another ex. chlorine atom (35Cl17) the outermost energy level of chlorine atom contains 7 electrons , so it can gain or share by one electron to complete its outermost energy level to 8 electrons. then we can say monovalent the atom which gain or share by one electron.





Divalent : ex. oxygen atom ( 16O8) the outermost energy level of oxygen atom contains 6 electrons , so the atom can gain 2 electrons or share with 2 of it's electrons with 2 electrons fo :

*another oxygen atom to form oxygen molecule O2

*two hydrogen atoms to form water molecule H2O.we can say atom which gain or share by 2 electrons is divalent





Trivalent : ex. aluminium atom (27Al13) the outermost energy level of aluminium atom contains 3 electrons that can be lost during the chemical reaction.



Ex. hydrogen is monovalent and no. of valency is 1 (one) .

magnesium is divalent and no. of valency is 2 (two).

aluminium is trivalent and no. of valency is 3 (three).



lithium = atomic no. = 3 , mass no. =7 , Li is monovalent can gain or share by 1( one ) electron.



I hope I can help you for best answer/

augmon