# Question 1b7a2

Mar 11, 2014

(a) The given formula is AlCl . It is incorrect. The correct formula can be written if we know the valencies of different elements. The valency of Aluminum is +3 as it loses three electrons to achieve stable noble gas configuration like Neon.
Each Chlorine atom has valency of -1 as it gains one electron to achieve stable noble gas configuration like Argon.

$A {l}^{3 +}$ , $C {l}^{1 -}$ To balance the positive and negative charges
for one Aluminum atom ,three chlorine atoms can unite as to make +3 charge equal to -3 charge.
So the formula will be $A {l}_{1} C {l}_{3}$

$N {a}_{3}$SO_#4 (incorrect). The valency of Sodium is +1 as it loses one electron to achieve stable noble gas configuration like Neon.
S${O}_{4}$ has valency of -2.
$N {a}^{1 +}$ S${O}_{4}^{2 -}$ To balance the positive and negative charges for one sulfate ion ,two Sodium atoms can unite as to make -2 charge equal to +2 charge.
So the formula will be $N {a}_{2} S {O}_{4}$

BaOH2 ( incorrect). The valency of Barium is +2 as it loses two electrons to achieve stable noble gas configuration.
Each Hydroxide Ion $O {H}^{- 1}$ has charge of -1 unit.
To balance the positive and negative charges
for one barium ion ,two hydroxide ions can unite as to make +2 charge equal to -2 charge.
$B {a}^{2 +}$ and $O {H}^{- 1}$ , So the formula will be $B {a}_{1} O {H}_{2}$

$F {e}^{2 +}$ , ${O}^{2 -}$ To balance the positive and negative charges for one oxide ion, one Iron atom can unite as to make -2 charge equal to +2 charge.
The formula is $F {e}_{2} {O}_{2}$ and simplifying it the formula will be
FeO