Guy

the number of electrons in the valence shell of elements a and b are 6 and 7 respectively. what is the formula and type of bonding in a compound formed by these elements?
a. a2b, covalent
b. ab2, covalent
c. a2b, ionic
d. ab2, ionic

If you would draw the Lewis structures of these atoms, you would see that A has 2 electron pairs and 2 lone electrons (that can bond). For B you’d see that you only have 1 electron that can form a bond. This means that 1 atom of A (2 lone electrons) can bond with 2 atoms of B. To know the kind of bond you have to know wether or not there will be a ‘donation’ of an electron from one atom to another. This happens when the number of electrons on one atoms is equal to the number of electrons another atom needs to reach the noble gas structure. As you can see, this is not the case here. This means that you get an AB2 structure with covalent character.