Chemistry test marking (1 Viewer)

[macrazy]

I have recently gotten my chemistry test back, and there are two multiple choice questions that I am confused about:
1) the valency of an atom is: (I answered "the number of electrons in the outer shell [energy level] of that atom) the correct answer was apparently "the charge on a positive or negative ion formed by that atom"
2) which of the following pairs of elements would most likely form an ionic compound: (I answered "bromine and sodium" ) the correct answer was "carbon and iodine"

I'm pretty confident with my understanding of chemistry, but I cannot work out why my answers were wrong... if someone could explain it would be great

 

[DepressedPenguino]

Technically, your answer for Q1 is correct..
For Q2, im confused... pretty interesting 0.0

 

[macrazy]

Question two was the one that really confused me, I thought that carbon and iodine both being non metals would form covalent bonds not ionic...

Sent from my GT-I9300 using Tapatalk

 

[strawberrye]

Technically, your answer for Q1 is correct..
For Q2, im confused... pretty interesting 0.0

For question two, if the question had asked about likelihood of ionic bonds, your answer should be correct because the nature of bonds between atoms also depends on the difference in electronegativity values, and the significant difference of electronegativity value of 1.9 between sodium and bromine suggests a high likelihood to form an ionic bond-perhaps ask your teacher to check over these questions again and ask them for a detailed explanation of why they have marked you wrong.

 

[QZP]

I have recently gotten my chemistry test back, and there are two multiple choice questions that I am confused about:
1) the valency of an atom is: (I answered "the number of electrons in the outer shell [energy level] of that atom) the correct answer was apparently "the charge on a positive or negative ion formed by that atom"
2) which of the following pairs of elements would most likely form an ionic compound: (I answered "bromine and sodium" ) the correct answer was "carbon and iodine"

I'm pretty confident with my understanding of chemistry, but I cannot work out why my answers were wrong... if someone could explain it would be great

Technically, your answer for Q1 is correct..
For Q2, im confused... pretty interesting 0.0

Valency IS NOT the # of outer-shell electrons. Where'd you learn that? Oxygen has a valency of 6 then?

 

[Crisium]

Valency IS NOT the # of outer-shell electrons. Where'd you learn that? Oxygen has a valency of 6 then?

^

It's the amount of electrons required to fill up the outtermost shell

So it's pretty much the charge of the ion of that element

 

[DepressedPenguino]

Q1 got me again! Dam.. haha. "Valency IS NOT the # of outer-shell electrons. Where'd you learn that? Oxygen has a valency of 6 then?" I always get tricked by that question :^(
IDK ABOUT Q2...take strawberrye's advice and ask ur teachee. Btw, u could've asked that period when u received ur exam paper?

 

[turntaker]

Yeah question 1 is not right. Their answer is right. For example if Carbon has 4 electrons doesn't mean that its valency is 4(oh wait it does.. bad example hehe). hmm for example Chlorine. It has 7 electrons in the outermost shell but the valency is not 7. Its 1- because it wants to gain 1 electron to fill the shell.

Question 2 is a bit tricky because Carbon is actually a metalloid and can sometimes bond ionically. Its very rare though. I would have chosen your answer. But as strawberrye said its to do with electronegativity.

 

[someth1ng]

For question two, if the question had asked about likelihood of ionic bonds, your answer should be correct because the nature of bonds between atoms also depends on the difference in electronegativity values, and the significant difference of electronegativity value of 1.9 between sodium and bromine suggests a high likelihood to form an ionic bond-perhaps ask your teacher to check over these questions again and ask them for a detailed explanation of why they have marked you wrong.

NaBr is a salt and hence, it must be ionic and carbon-iodine bonds are definitely covalent such as in iodomethane.

I would be careful with using electronegativity to determine if a bond is ionic or covalent because you can have large differences in electronegativity and still have a covalent bond (H-F, Si-F etc). The difference in electonegativity of 1.7 is only a "rule of thumb" - it isn't always right.

I suggest following a rule like this: molecular compounds always have covalent bonds and salts (metal+non-metal) always have ionic bonds.

 

[macrazy]

Thank you all for your help with question one, I must have misunderstood that bit when we were learning about it, but now that you've pointed it out it makes a lot more sense