## Ch 3 #9,11 [ENDORSED]

704709603
Posts: 92
Joined: Wed Sep 21, 2016 2:59 pm

### Ch 3 #9,11

Hi,
Can anyone explain 3.9 and 3.11 please?

Thank you!

shannon_tseng_3L
Posts: 20
Joined: Wed Sep 21, 2016 2:56 pm

### Re: Ch 3 #9,11  [ENDORSED]

for these kinds of problems, it's helpful to count the total e-'s this metal M has.

for 9a:
the element in question is [Ar]3d^7
you know that argon has 18 e- (from periodic table: # e- = atomic #)
and then you add 7 more from the 3d^7
18+7= 25
but you can't stop there since the metal M has a +2 charge
25+2= 27, the # of e- in Co, which is also the answer (Co^2+)
it makes sense if you think about it backwards: Co^2+ has the same e- configuration as Mn w/o any charge ([Ar]3d^7), which has 25 e-'s (a number we got before adding 2 in the final step)

the other problems are all pretty similar

Manpreet Singh 1N
Posts: 41
Joined: Wed Sep 21, 2016 2:59 pm
Been upvoted: 1 time

### Re: Ch 3 #9,11

Hello,

So basically for this question, we are told to find a M (a metal) with the corresponding configurations. So for part a of #9. it is [Ar]3d^7.
To begin we look at the noble gas [Ar], that is our starting point. Then we look at the next part, which is 3d^7. The first row of the d series is 3d. So we go to the 7th element in that period. So 1 would be Sc, 2 would be Ti, etc. We are looking for 7 in this case and that is Co.
#9 says that metal is M^2+, so the answer is Co^2+.

you do the same thing for the rest of 9 and 1. However 11 is a metal with 3+.

Hope that helps :)

704709603
Posts: 92
Joined: Wed Sep 21, 2016 2:59 pm

### Re: Ch 3 #9,11

With a +2 charge shouldn't we subtract 2 from 25?

TiengTum2D
Posts: 19
Joined: Fri Jul 22, 2016 3:00 am
Been upvoted: 1 time

### Re: Ch 3 #9,11

A metal with a +2 charge that has 25e- means the neutral atom would have a total of 25+2=27e- (which is the element Cobalt) because a positive charge means that electrons were lost when bonding.

704709603
Posts: 92
Joined: Wed Sep 21, 2016 2:59 pm

### Re: Ch 3 #9,11

Oh, I understand! Thank you!