Isotope Explanation (split)

[julie S]

Hi There,

I am new to this discussion site but have enjoyed reading questions and answers for a while now. I am a secondary science teacher and am interested in opinions on the best way to educate and explain what isotopes are. Year 10's are intelligent and pick up very qickly. I find it hard not to cause confusion in the topic???

Cheers, Julies

[insane_alien]

start off by explaining the components of the nucleus and how it is the number of protons that defines the element(if you haven't already) and then just flat out tell them that isotopes are atoms with the same number of protons but different numbers of electrons.

 

note to mods: recomend the isotope discussion gets moved to its own thread

[YT2095]

tell them that isotopes are atoms with the same number of protons but different numbers of electrons.

 

don`t you mean Neutrons?

[insane_alien]

$£%£$%^£$^

 

yes i meant neutrons whoopsie.

[swansont]

I like to tie things back to the physical reasoning, rather than just memorizing a definition.

 

Chemical reactions are caused by the electron structure, and for a neutral atom, the number of electrons equals the number of protons. That's what gives you the identity of the element — the number of protons. That's why we distinguish different elements, because they react differently with other elements.

 

Neutrons are neutral and don't affect the electron count, so the chemistry is largely unaffected — Carbon will form the same bonds whether it has six neutrons or seven or eight (however, there can be some subtle effects, e.g. different reaction rates from mass changes, which are probably unimportant at this level). Changing the neutron number does affect nuclear behavior, and can turn a stable isotope into an unstable one (or vice-versa), so that's very important, too, but to different people. In this case, you might look at C-14, and how you can do radiocarbon dating because of this.

[antimatter]

I learned about isotopes in 8th grade, and my science teacher did the same thing that insane_alien recommended. We already knew the components of a nucleus (I did, at least), but he just went over it once then said that an isotope was an atom with a different amount of neutrons in its nucleus.

I think everyone got it fairly quickly.

[hermanntrude]

depending on how advanced the course is and just how far your students are likely to delve into chemistry, one good way is to show them atomic structure as far as the bohr theory (which like so many things in chemistry is wrong, but a very useful lie), then consider the hydrogen atom, and ask them what effect changing the number of electrons would have, then repeat for protons and repeat for neutrons. This gives them a good idea of what it means to have a proton number, a charge and a mass.

[julie S]

Thanks guys for your input - it gave me some good tips and ideas.

Cheers,

Jules