[RGraham9]

Hi guys , I need help in understanding why Isotopes have different physical properties. My textbook says that Isotopes have different physical properties as isotopes have different number of neutrons. The difference in the number of neutrons affect the "mass" and the physics properties of a substance is affected by this "mass".

This "mass" they are referring to , is it the Nucelon Number (Amount of Protons and Neutrons / Nucleons making up the Nucleus of one atom) ?

Thanks Guys ! Appreciate It !

[thetada]

Yes exactly, electrons have virtually no mass, so all the mass comes from the nucleons. Isotopes behave the same chemically, but their masses are different.

[RGraham9]

Okay so just to reaffirm my understanding , the difference in physical properties of isotopes is a result of the difference in the nucleon masses of one atom in each of the different isotopes correct ?

[RGraham9]

Corrections regarding my previous statement :
Nucleon Number (Mass Number ) not Nucleon Masses

[thetada]

Okay so just to reaffirm my understanding , the difference in physical properties of isotopes is a result of the difference in the nucleon masses of one atom in each of the different isotopes correct ?

I think I agree but the "one atom" bit has thrown me.

The difference in physical properties of isotopes is a result of the difference in the nucleon number between the atoms of the different isotopes.

[RGraham9]

Sorry about throwing you off with the one atom thing.  The reason I said 1 atom was because :

• From what I have read / definition of Nucleon Number/Mass Number : The nucleon number / nucleon mass is the total number of protons and neutrons of an atom of an element.
• My textbook says that the physical properties of a substance is affected by "mass" , hence I was wondering if this "mass" was actually a reference to the Mass Number / Nucleon Number of the substance. (E.g The physical properties of a substance is affected by its Nucleon Number / Mass Number.)
• Thus , with reference to the definition of the Nucleon Number / Mass Number (in bullet point 1) and bullet point 2 , won't that mean that the physical properties of a substance is affected by one atom due to its mass number ?

This is very confusing to me but I appreciate the help provided by you so far.

[thetada]

Let's imagine two hypothetical clumps of carbon. Clump 1 contains 10 atoms, each of which has 6 protons and 6 neutrons. Clump 2 also contains 10 atoms. 9 of those atoms are the same as those in clump 1, while the 10th has 6 protons and 7 neutrons. In this case, clump 1 and clump 2 are not isotopes, rather, the 10th atom in clump 2 (the one with 7 neutrons) is an isotope of all the other atoms. However, you are right in saying that the overall mass of clump 2 would be greater than the overall mass of clump 1. But again, that doesn't make the clumps isotopes, but is rather explained by the presence of a different isotope in clump 2.

[AdiDex]

Chemical reaction is all about  forming new bonds and breaking old bonds , How easily(fast) a bond will form and how easily(fast)  you can break old bonds . How strong a bond is forming and how much old bond was weak . These are the factors which study during the chemical reaction(not in case of nuclear reaction) .

An isotope have same no. of electron (so there is no big deal )  even it has same no. of protons ( So those "same no." of electrons are bounded exactly in the same way as they were bounded in  the other isotope ) , what actually changed is no. of neutron that will cause little bit change in gravitation force and reduced mass . You should know the fact Gravitation force is much weaker force (I'm not talking about black holes ) than that of electrostatic force (if we're talking about atoms).  So there will be no major change in the chemical properties .

Yup in case of boiling point , density - They will get change as they have to do something with mass . 

P.S. Bonds are lie , and we should use the word Overlapping of orbitals .

[AdiDex]

Sorry i didn't read your whole question , i just read  "I need help in understanding why Isotopes have different physical properties" . You can ignore my above post . it was in other context .

[RGraham9]

@AdiDex : It's okay
@thetada : So basically ,
• Isotopes are atoms of the same element with different numbers of neutrons.(Aren't elements)
• The presence of isotopes in different amounts , in the same elements , results in different physical properties between the identical elements due to the difference in the relative atomic mass of the two identical elements ?
(Sorry if I get this wrong again. Trying my best.)

[thetada]

• Isotopes are atoms of the same element with different numbers of neutrons.(Aren't elements)
• The presence of isotopes in different amounts , in the same elements , results in different physical properties between the identical elements due to the difference in the relative atomic mass of the two identical elements ?

bullet 1: isotopes are the same element
bullet 2: Yes, the difference in physical properties is caused by the different numbers of neutrons (which in turn affects relative mass). For example, carbon-14 is less stable than its isotope carbon-12, and hence radioactive. This difference forms the basis of carbon dating.

If you have just one atom of each isotope, you can say that the atoms have different physical properties. In this example, carbon-14 is radioactive, whereas carbon-12 is not.

As you point out, two pieces of carbon could have different proportions of each of the carbon isotopes. So in that sense, we can say that the pieces of carbon have different physical properties, but most of those differences operate at the atomic level. For example, if one piece did contain carbon-14, but the other did not, we could say that only the carbon-14-containing piece was radioactive, but that radioactivity will operate at the atomic level, that is, individual atoms will undergo radioactive decay.

[Burner]

• The presence of isotopes in different amounts , in the same elements , results in different physical properties between the identical elements due to the difference in the relative atomic mass of the two identical elements ?

I would say 'relative isotopic mass' or 'atomic mass' rather than 'relative atomic mass'. Definition of relative atomic mass:(From http://www.ausetute.com.au/atomicmass.html)

The relative atomic mass, or atomic weight, of an element is the weighted average of the masses of the isotopes in the naturally occurring element relative to the mass of an atom of the carbon-12 isotope which is taken to be exactly 12.

[RGraham9]

Unfortunately , I am still a bit confused by Isotopes. (Argh , sorry for wasting your time , I feel really bad for doing this.)
• So Isotopes are atoms of the same elements with different neutron numbers correct ?
• Isotopes have different mass numbers.
• In my textbook it mentions that "Isotopes have different physical properties." This is basically saying that identical elements ,
made up of different atoms with different proton numbers / isotopes will result in both the identical elements being different in terms of their physical properties and that this is the result due to the difference in the mass numbers of the isotopes of the different elements correct ?
• If the above is correct , how does the difference in mass number / nucleon number of isotopes actually affect the physical properties of that element ?
• So let's say that there is a element that is entirely made out 99 atoms and that all the 99 atoms have 6 protons and 6 neutrons. If somehow (even if this is impossible scientifically) I am able to change one of the atoms to 6 protons and 6 neutrons instead , will the physical properties of the element change drastically ? (E.g boiling point , melting point or density.)
• Lets say that we have an element entirely made out of 10 atoms. like the carbon example , and all atoms have 6 protons and 6 neutrons . On the other hand we have another identical element and that identical element has 10 atoms. However 9 of the atoms have 6 protons and neutrons while the last atom has 6 protons and 7 neutrons. Hence the mass number of the 6protons and 6neutrons atoms will be 12 while the isotope will be 13. How does this isotope (mass number 13) cause a change in the physical properties of that elements ?

Really really appreciate the help. Thank you so much and sorry for stealing your time guys.

[AWK]

Compare properties of H₂O and D₂O in wikipedia.
https://www.wikiwand.com/en/Heavy_water
Look also at the toxicity of D₂O in this article. This means that stable isotopes may show different chemical reaction in living organisms.
The textbook informations are only a selection of properties.

[Borek]

let's say that there is a element that is entirely made out 99 atoms

You mean there are only 99 atoms of the element? Your statement "entirely made of 99 atoms" doesn't make much sense.

atoms have 6 protons and 6 neutrons. If somehow (even if this is impossible scientifically) I am able to change one of the atoms to 6 protons and 6 neutrons instead

Changing 6/6 to 6/6 doesn't change anything.

element entirely made out of 10 atoms

Again, not clear what you mean.

we have another identical element and that identical element has 10 atoms

What do you mean by "identical element"?

I wonder if there is not some underlying misunderstanding that makes you confused.

Or perhaps sometimes you mean "another sample of an element, sample made of different isotopes"?