What is an Isotope?

[Birt]

You hear about different isotopes for elements eg uranium. What exactly is an Isotope and are these just for elements?

[Hamish]

The cemistry of an element is dictated by the number of electrons and therefore protons it contains. Each element has a different number of each. However the neuclius of an atom also contains nutral nutrons. Elements may contain different number of neutrons but have the (essencially) same chemical properties, these are call isotopes. Only a few elemts have only one natrually occouring isotope, most have atlease 2 or 3. Some isotopes of radioactive elements are more easily broken up during fission and are therefore important in power generation and bomb making. For Uranium the most common is U238 (99.275%), but U235(0.72%) is the important one for most fission applications, there is also a natrually occouring U234 (<0.005%). In some reactors U233 is also produces by neuclear reactions, this can also be used in fission applications.

Another commonly heared about isotope and isotope of hydrogen (1 proton, 1 electon, 0 neutrons) is deuterium (1 proton, 1 electon, 1 neutrons), which is not radio active and D2O is called heavy water. The other isotope of hydrogen is Tritium (1 proton, 1 electon, 2 neutrons) but this has to be made by neutron bombardment of deuterium and is radioactive.

I hope this is understandable as I have assumend you know about protons, neutrons and electrons......

[Loosehead]

In a nutshell and isotope is the name given to each of the configurations of atom for a given element, there is usually > 1 istopes for an element.

[violetblue]

Put simply:
Atomic number of a substance = the number of protons and electrons it has (eg carbon has 6 protons and 6 electrons, therefore its atomic number is 6).

Atomic weight of a substance = the atomic number + the number of neutral neutrons (chemically inactive) the substance has.

Isotopes are variations of the same substance (with the same atomic number) but with different atomic weights (the atoms of different isotopes have the same atomic number as each other but have different numbers of neutrons in the atoms, ie different atomic weights.