By which physical properties do isotopes actually differ

[IndianScientist]

Hello to any wonderful scientist reading this,this might be and can be a really foolish doubt (because of which I seek my deepest apologies for posting in a intellectual and scientifically tempered community,where many of you are also too busy to handle such queries) but this is really bothering me lately .

Isotopes are atoms of the same element having same atomic number but different mass number . This means that they differ in their physical properties(since the protons And electrons are same in number And neutrons are different, and the neutrons are the subatomic particles which influence the physical properties of an element ) And we generally refer the physical properties as melting and boiling point, electrical conductivity , physical state ,etc. But what are actually these physical properties? Will liquid oxygen and gaseous oxygen be considered Isotopes (since the physical property by virtue of which they differ is the physical state) . They can not be considered isotopes because the difference in physical state was caused by the difference of the INTERMOLECULAR space and force and so ATOMS have nothing to do with it. Also , Electrical conductivity depends on the presence of free electrons and since no. of electrons are same in isotope , the neutrons (by virtue of which the isotopes differ) have nothing to contribute towards electrical conductivity. So what are these physical properties and how do they differ in isotopes.

 

[John Cuthber]

You seem to have it the wrong way round.
The definition of isotopes is that they have different numbers of neutrons.

Cooling oxygen until it liquefies does not change the number of neutrons.
So it does not make any new isotopes.

What changes is the temperature, rather than anything else.
 

 

Isotopes have slightly different boiling points, but it is not the change in boiling point that makes them different isotopes.

[IndianScientist]

9 minutes ago, John Cuthber said:

You seem to have it the wrong way round.

41 minutes ago, IndianScientist said:

 

Isotopes are atoms of the same element having same atomic number but different mass number . This means that they differ in their physical properties(since the protons And electrons are same in number And neutrons are different, and the neutrons are the subatomic particles which influence the physical properties of an element ) And we generally refer the physical properties as melting and boiling point, electrical conductivity , physical state ,etc. But what are actually these physical properties

 

 

I mentioned in my query that isotopes have different no. of neutrons. I asked what physical properties do they differ in? Do they ast all differ in physical properties?

[exchemist]

5 minutes ago, IndianScientist said:

I mentioned in my query that isotopes have different no. of neutrons. I asked what physical properties do they differ in? Do they ast all differ in physical properties?

Barely. With deuterium you can see some differences from regular hydrogen but that's because the mass is doubled. This affects things like some spectroscopic properties and reaction rates a bit. With heavier elements to a first approximation they don't differ.  

[studiot]

1 hour ago, IndianScientist said:

I mentioned in my query that isotopes have different no. of neutrons. I asked what physical properties do they differ in? Do they ast all differ in physical properties?

Indeed you did.

But John is right that you seem to be a bit confused about what is an isotope.

Perhaps you are mixing this up a bit with allotropy or perhaps it is just a language difficulty.

You also mentioned physical properties only.

Physical properties are rather more affected than chemical ones because the extra neutrons add extra mass, but not charge.

So properties that depend upon atomic or molecular mass such as colligative properties do vary a bit.

International tables such as Lange give values for these for different isotopes where they are known.

Within the atom most electron orbitals stay the same and the number of electrons stays the same to spectra from these (X ray and UV) are pretty much the same, as are the actual chemical reactions involved. So dielectric and magnetic properties that depend upon electron spin will be unaffected but NMR spectra are changed.

https://www.osti.gov/biblio/6389648-proton-deuterium-tritium-nuclear-magnetic-resonance-intramolecular-hydrogen-bonds-isotope-effects-shape-potential-energy-function

But IR spectra are dependant on vibrating atomic masses so will change the most.

As already noted by exchemist mass spectra are clearly affected and a very important method of both istope detection and separation.

 

However some bond strengths and/or angles can be altered.

https://pubmed.ncbi.nlm.nih.gov/15137048/

 

 

 

[Bufofrog]

4 hours ago, IndianScientist said:

the neutrons are the subatomic particles which influence the physical properties of an element ) And we generally refer the physical properties as melting and boiling point, electrical conductivity , physical state ,etc.

That is not correct.  The physical properties an element are due to the number and configuration of the electrons, properties are not due to the number of neutrons.

[TheVat]

Heavy water has a different refractive index, viscosity, BP, heat of fusion, etc.   

[Sensei]

Quote

By which physical properties do isotopes actually differ

There are ~ 3131 isotopes of 118 elements. The vast majority unstable or extremely unstable. Which one do you want to know? You need to be specific. The vast majority of these isotopes have not been isolated in sufficient quantity to properly test their physical and chemical differences from the most abundant stable isotopes of the element. The differences between the isotopes are used to isolate them. The most noticeable differences are only apparent at the quantum level, i.e., to isolate a single isotope or element, a mass spectrometer can be used. Isotopes/elements with different m/e deflect differently in a strong magnetic field and accelerate differently (due to mass difference) in an electric field.

Mass vary significantly from isotope to isotope, from element to element. In the case of Hydrogen-Deuterium-Tritium it is +100% / +200%. In the case of Uranium-235 vs U-238 it is just +1%...

 

Edited December 17, 2021 by Sensei

[Bufofrog]

3 hours ago, TheVat said:

Heavy water has a different refractive index, viscosity, BP, heat of fusion, etc.

The OP was asking about elements.

[TheVat]

6 hours ago, Bufofrog said:

The OP was asking about elements.

If the hydrogen isotope in a water molecule makes a difference as to the properties of the molecule, then it would seem that the neutron number makes some difference in that atom's physical properties.  So I was questioning your original statement that "physical properties...are not due to the number of neutrons."   How an atom interacts with another atom would be an aspect of its physical properties, no?  Deuterium and hydrogen interact differently, a bit, in a water molecule.  

[Bufofrog]

59 minutes ago, TheVat said:

If the hydrogen isotope in a water molecule makes a difference as to the properties of the molecule, then it would seem that the neutron number makes some difference in that atom's physical properties.  So I was questioning your original statement that "physical properties...are not due to the number of neutrons."   How an atom interacts with another atom would be an aspect of its physical properties, no?  Deuterium and hydrogen interact differently, a bit, in a water molecule.  

Yes you are correct heavy water has some slightly different properties than normal water due to the higher mass of the heavy water molecule.  These are subtilties that I don't think the OP is asking about, he does not seem to understand that the chemical properties of the elements are to the most part due to the electrons configurations in the elemental atoms.