Forgot certain concepts. Just want to clarify.
Say you have an equation
2Na + 2H2O -> 2NaOH + H2
If i want to calculate the number of moles of (eg. Na) i just take the mass/ar
For the Ar part, just needa write 23 and not (2 X 23) right? the '2' is only used for comparison of mole ratio am I correct? suddenly forgot this while i was doing mole concept hahah! was doing the chem questions so happily that I forgot the basic stuff suddenly!
And there is this question I do not quite understand
What do both an atom and an ion of the isotope of sodium with nucleon no. 23 and proton no. 11 Na, contain?
A 11 electrons
B 12 neutrons
C 23 protons
D 23 neutrons
Answer is B. But why should it both be 12? after all they already said the atom and ion of Na are isotope of Na? That's why I eliminated option B and D initially.
yup. 1st part you're right. Mr/Ar does not include Mol value.
for the 2nd part....
Do note. a sodium atom Na -- has no charge, and has 11 electrons in total, with 1 electron in its valence shell. It can exist as a metal, but not as an atom by itself, if not it would be a free radical ( which btw, im not sure if Na can exist as a free radical). yup. and it has a neutron amt of ---> 23-11 = 12
---------------------------
Now, a sodium ion has a charge of +1. and it has 8 valence electrons. NOTE: that the amount of protons do NOT change. Since number of protons do not change (although the amt of electrons do), the amt of neutrons of the Na+ ion is => 23-11= 12
* then you might be asking, ---- i thought i learnt that.....proton amt= electron amt!!. however, for the Na+ ion, the extra electron is GIVEN away, and there is NO neutrons/protons being transferred.
hope that this clears things up
Originally posted by bonkysleuth:And there is this question I do not quite understand
What do both an atom and an ion of the isotope of sodium with nucleon no. 23 and proton no. 11 Na, contain?
A 11 electrons
B 12 neutrons
C 23 protons
D 23 neutrons
Answer is B. But why should it both be 12? after all they already said the atom and ion of Na are isotope of Na? That's why I eliminated option B and D initially.
There is a very common misconception among both 'O' and 'A' level students (and teachers!). Many students write the definition of isotopes as :
"Isotopes are atoms with the same no. of protons but different no. of neutrons."
WRONG.
Isotopes are NOT atoms. They are "types" of an element (and elements are defined by their unique number of protons).
The correct definition of isotopes is :
"Isotopes of elements have atoms/ions, that have the same number of protons but different number of neutrons."
Hence, for any given isotope of an element, eg. the isotope of sodium with nucleon no. 23, the Na atom and the Na+ ion will BOTH contain :
11 protons
12 neutrons
The only difference between an atom and an ion (of the same isotope) is of course, the number of electrons (Na atom has 11 electrons, Na+ ion has 10 electrons).
Let me revise the phrasing to make it even clearer and easier to understand. The correct definition of isotopes is :
"Different isotopes of the same element, have atoms/ions that have the same number of protons but different number of neutrons."
If you're talking about two different isotopes of the same element, eg. Cl-35 and Cl-37, then an atom of Cl-35 and an atom of Cl-37 both have 17 protons and 17 electrons, but the Cl-35 atom has 18 neutrons while the Cl-37 atom has 20 neutrons.
Comparing ions (in this case, Cl- ion) of the two isotopes will yield the same observation as above in terms of protons and neutrons, except that both ions will have 18 electrons (instead of 17 electrons).
Comparing an atom of one isotope versus an ion of another isotope, for the same element, you should see that the two species (atom of isotope #1 vs ion of isotope #2) will have different number of neutrons and different number of electrons, only their number of protons will be the same (since they are of the same element).
Originally posted by UltimaOnline:
The correct definition of isotopes is :
"Isotopes of elements have atoms/ions, that have the same number of protons but different number of neutrons."
Hence, for any given isotope of an element, eg. the isotope of sodium with nucleon no. 23, the Na atom and the Na+ ion will BOTH contain :
11 protons
12 neutrons
The only difference between an atom and an ion (of the same isotope) is of course, the number of electrons (Na atom has 11 electrons, Na+ ion has 10 electrons).
wa... need time to digest. yawnz
but already say is isotope so at least neutron should have difference? o.o
Originally posted by yiha093:wa... need time to digest. yawnz
but already say is isotope so at least neutron should have difference? o.o
They specified the SAME isotope. Only DIFFERENT isotopes of an element will have different number of neutrons.
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Originally posted by UltimaOnline:
They specified the SAME isotope. Only DIFFERENT isotopes of an element will have different number of neutrons.
ok i understand but where got same same isotope?? ._.
isnt shown in the qn?
Originally posted by yiha093:
ok i understand but where got same same isotope?? ._.isnt shown in the qn?
For the question "What do both an atom and an ion of the isotope of sodium with nucleon no. 23 and proton no. 11 Na, contain?"
Do you read the above as meaning :
"What do both an atom and an ion of the (same) isotope of sodium with nucleon no. 23 and proton no. 11 Na, contain?" (correct interpretation)
or
"What do both an atom and an ion of the (different) isotope(s) of sodium with nucleon no. 23 and proton no. 11 Na, contain?" (wrong interpretation)
You have to interpret the question correctly.
i interpret the qn as.
atom de isotop and ion de isotope with 23 neu.no. and 11 proton.no.
how??
Originally posted by yiha093:i interpret the qn as.
atom de isotop and ion de isotope with 23 neu.no. and 11 proton.no.
how??
Perhaps other students here can try to explain to yiha093 in an alternate way, that may be easier for him to understand.