[T]

Hello,

How do isotopes change the atom? For example, does it change it's chemical reactivity, stableness etc.

Please try to write as many points (but within high school)

Thanks

[Babcock_Hall]

Forum Rules require you to show an attempt before we can help you.  Maybe a good place to start is for you to tell us what an isotope is, or give an example of one.

[T]

Ok, this wasn't a homework question so I didn't give my working.

As I know, isotopes are same elements with different number of neutrons. An example of isotopes are C-12 and C-14.

[Babcock_Hall]

You probably know that C-14 is radioactive but C-12 is not.  So one thing that is different is stability.  C-13 is another isotope of carbon.  There is a technique that looks at the way the nuclei of atoms interact with radio waves (nuclear magnetic spectroscopy) called NMR for short, and it can detect C-13 but not C-12.

[Enthalpy]

Chemical properties depend on electrons and these interact much with protons but little with neutrons. The general consequence is that isotopes' chemical properties are very close.

The one well-known exception is hydrogen. Deuterium gives to molecules (usually water) chemical properties that differ enough to be exploitable by chemical means: different acidity, melting and boiling point.

To a lesser degree, lithium 6 and 7 differ a bit chemically. Hard to exploit.

Physical properties can depend little or much on the number of neutrons. Radioactivity changes radically, RMN properties too. The rate of diffusion and the effect of centrifugal force depend on the mass or its square root, hence not much, but are used to separate isotopes.

One bizarre effect: ⁴He becomes a superfluid around 2K while ³He needs a few mK. There is no consensual explanation to that.

[Vidya]

main difference in the atoms of the isotopes is the mass of the nucleus and hence stability also .

[Babcock_Hall]

Reactions are often, although not always, slower when a heavier isotope substitutes for a lighter one.  The effect can be quite small, such as a few percent difference.  However, it can provide mechanistically useful information about the reaction.

[T]

Thank you very much everyone.

So more neutrons makes the atom more stable right?

[Arkcon]

You can investigate the trend on the periodic table.  For lower atomic numbers, on rule holds, then eventually, another rule holds, then eventually at higher atomic numbers nothing keeps an atom stable.

[Enthalpy]

About as many neutrons and protons make a nucleus more stable. Exceptions:
- Hydrogen doesn't need a neutron;
- take a bit more neutrons for heavier elements.
http://en.wikipedia.org/wiki/Table_of_nuclides

When a nuclide has too many protons or too many neutrons, it emits a beta plus or a beta minus to transform a proton in a neutron or vice versa and approach the optimum. Most elements have little choice for their number of neutrons, like +-2 neutrons for stable isotopes and +-10 for observed isotopes.

A single neutron is unstable. In a quarter hour, it has probably transformed in a proton, electron and antineutrino. Aggregates of two or four neutrons are not bound, and the observation of aggregates of two protons is doubtful
http://en.wikipedia.org/wiki/Dineutron#
http://en.wikipedia.org/wiki/Diproton#
so a stable nucleus needs the proper amount of neutrons and protons. Throwing any number together doesn't suffice.