its 25 years since i was at school and this is tough getting going how do i work out the formula for?

Question

lithium oxide i know its li2o but want to know how i get it
ta
ian

Answer 1

Lithium (Li) is in Group I of the periodic table so it can only lose one(1) electron.
Oxygen (O) is in Group VI of the periodic table, so it can only gain two(2) electrons.
So for Oxygen to gain two electrons it receives one each from two Lithium's. Hence 2 Li's and 1 O in the formula. (Li2O).

N.B.
Groups 1,2 & 3 in the Periodic Table lose the corresponding numbers of electrons as the Group number.
Groups 5,6 &7 in the Periodic Table gain electrons
Group 5 gains three electrons
Group 6 gains two electrons
Group 7 gains one electron.
Group 4 is a special case as is Group 8(0) the noble gases, and the Transition Metals.
Essentially, an atom when being ionised will lose or gain electrons to ccomplete an '8' membered octet of electrons.

Answer 2

You need to know that Li ion always has a valence of +1
You need to know that O almost always has a valence of -2
The compound, lithium oxide, must be neutral, so you need 2 lithiums for 1 oxygen: Li2O.

When Group 1A elements (in the periodic chart) combine with other elements, the group 1A elements have a valence of +1 (i.e., they have lost 1 electron): H+, Li+, Na+, K+, etc.

Answer 3

lithium has valency 1
oxygen has valency 2

Li(superscript 1) + O(2)

cross multiply
li(subscript 2)O

Lio2