I need a SERIOUSLY dumbed down explanation.
girl child has to do some chem as part of her psychology degree.
The unit she’s doing (I assume anywhere between a week and a semester, not sure) took two years in high school.
the one that sticks in my head is uranium 235 and 238.
what I don’t get is this…lets take selenium (cos I reckon it sounds pretty).
so we have selenium 34 yes? if we “isotope” it to selenium 36 it becomes krypton.
I am SO not understanding this stuff at all

>so we have selenium 34 yes? if we “isotope” it to selenium 36 it becomes krypton.

No.

An element is ‘defined’ by the number of protons it has in its nucleus.

Now included in the nucleus is also a number of neutrons. The number of neutrons can vary, and this changes the isotope.

So uranium has 92 protons, which defines it as ‘uranium’. The number of neutrons it has changes the isotope. Uranium-238 has 146 neutrons which added to 92 protons gives the figure 238.

I’m sure someone else will come along soon, but in general terms:

Isotope means same number of protons in the nucleus, but either slightly more or less neutrons.

The protons have a positive electrical charge which therefore means they have the same number of negatively charge electrons. It’s the number of electrons that determine the chemical properties. Since neutrons have a neutral electrical charge, having more or less of them doesn’t make a difference to the chemical properties, it just makes then heavier or lighter.

However, having an unbalanced number of protons and neutrons can lead to radioactive decay – an number of different processes where an proton can turn into a neutron or vice versa, and either absorb or emit a combination of energy, smaller nuclei, electrons, neutrinos etc. When it changes the number of protons it becomes a different element with different chemical properties.

so does this naturally occur?
can we reduce the neutrons in selenium to make it an isotope?
and why, if the neutrons aren’t the same, is it the same element.
you probably already said it in some way but I’m not getting it

>so does this naturally occur?

Yep, Purps, all naturally occuring.

>can we reduce the neutrons in selenium to make it an isotope?

It is already an isotope. As far as I know every element has different isotopes. That is, there are different total numbers of ‘bit’ in the nucleus, where the bits consist of protons and neutrons.

>and why, if the neutrons aren’t the same, is it the same element.

The number of neutrons in an element don’t change its elemental properties :) Basically, the chemical properties of an element are set by the number of protons in its nucleus.

sibeen said:

>so does this naturally occur?

Yep, Purps, all naturally occuring.

>can we reduce the neutrons in selenium to make it an isotope?

It is already an isotope. As far as I know every element has different isotopes. That is, there are different total numbers of ‘bit’ in the nucleus, where the bits consist of protons and neutrons.

>and why, if the neutrons aren’t the same, is it the same element.

The number of neutrons in an element don’t change its elemental properties :) Basically, the chemical properties of an element are set by the number of protons in its nucleus.

….which equals the number of electrons, which more actively participate in chemical bonding and the like.

morrie said:

sibeen said:

>so does this naturally occur?

Yep, Purps, all naturally occuring.

>can we reduce the neutrons in selenium to make it an isotope?

It is already an isotope. As far as I know every element has different isotopes. That is, there are different total numbers of ‘bit’ in the nucleus, where the bits consist of protons and neutrons.

>and why, if the neutrons aren’t the same, is it the same element.

The number of neutrons in an element don’t change its elemental properties :) Basically, the chemical properties of an element are set by the number of protons in its nucleus.

….which equals the number of electrons, which more actively participate in chemical bonding and the like.

I was trying to keep electrons out of it, Morrie.

I do realise that these pesky little buggers do the ‘chemical shit’ (technical term), but I’m trying not to confuse Purps.

Relying on the number of electrons to define the element would be a bit of a bugger with something like copper when it is passing a current.

Oh, it’s copper.

No, it’s not.

Oh, it’s copper.

No, it’s not.

Oh, it’s copper.

No, it’s not.

Oh, it’s copper.

No, it’s not.

:)

purple said:

I need a SERIOUSLY dumbed down explanation.
girl child has to do some chem as part of her psychology degree.
The unit she’s doing (I assume anywhere between a week and a semester, not sure) took two years in high school.
the one that sticks in my head is uranium 235 and 238.
what I don’t get is this…lets take selenium (cos I reckon it sounds pretty).
so we have selenium 34 yes? if we “isotope” it to selenium 36 it becomes krypton.
I am SO not understanding this stuff at all

my understanding for what its worth

an isotope is simply the same element with a differing number of neutrons in the nucleus, chemically they act the same because they all have the same number of proton but they have different numbers of neutrons.

element X

isotope 1 of element X – no neutrons
isotope 2 of element X – 1 neutron
isotope 3 of element X – 2 neutrons

congartulations!!

you now know what an isotope is!

> lets take selenium (cos I reckon it sounds pretty). so we have selenium 34 yes? if we “isotope” it to selenium 36 it becomes krypton.

No. Let’s add some neutrons. Selenium has 34 protons. It has five stable isotopes. Add more neutrons and it decays by beta radiation (a neutron becomes a proton) to bromine. Add enough neutrons to bromine and one will decay by beta radiation to give krypton. Krypton has 36 protons.

The chemical properties of an element are almost independent of the number of neutrons, but strongly depend on the number of protons because in order to be electrically neutral an atom must have the same number of electrons as protons. It’s the number of electrons and how they are arranged in shells that governs the chemistry.

I “thought” that the number of protons and neutrons were the same.
or is it protons and electrons?
BUT…now I (kinda) get that electrons are not doing any isotoping I think I can explain it to her a bit better.
Going to find a periodic table that shows me how many p n and e each element has so I can explain it to myself.
thanks peeps :)

purple said:

I “thought” that the number of protons and neutrons were the same.
or is it protons and electrons?
BUT…now I (kinda) get that electrons are not doing any isotoping I think I can explain it to her a bit better.
Going to find a periodic table that shows me how many p n and e each element has so I can explain it to myself.
thanks peeps :)

http://www.ptable.com/#Isotope

You can click on an element and get a list of its isotopes. You’ll notice they all have the same atomic number, ie the same number of protons.

1. Protons – determines which element it is
2. Protons and electrons – determines how it behaves chemically
3. Protons and neutrons – determines its isotope and stability (radioactivity)

purple said:

I “thought” that the number of protons and neutrons were the same.
or is it protons and electrons?
BUT…now I (kinda) get that electrons are not doing any isotoping I think I can explain it to her a bit better.
Going to find a periodic table that shows me how many p n and e each element has so I can explain it to myself.
thanks peeps :)

an element is defined by the number of protons it has
eg
element X has 1 proton

an isotope is element X with either neutrons or none, it is still element X but a particular breed of element because of its differing numbers of neutrons in it

eg

the isotopes of element X
they all have one proton but differing numbers of neutrons as you can see below

element X isotope 1: no neutrons
element X isotope 2: 1 neutron
element X isotope 3: 2 neutrons

Twoy said:

1. Protons – determines which element it is
2. Protons and electrons – determines how it behaves chemically
3. Protons and neutrons – determines its isotope and stability (radioactivity)
   

Those numbers were supposed to the the # sign, not numbers. In other words “the number of protons”, etc.

>Protons and neutrons – determines its isotope and stability (radioactivity)

When I was studying this, many, many moons ago, it was theorised that there was an “Island of Stability’ up around element 120, or thereabouts.
Has this come any closer to being discovered?

sibeen said:

>Protons and neutrons – determines its isotope and stability (radioactivity)

When I was studying this, many, many moons ago, it was theorised that there was an “Island of Stability’ up around element 120, or thereabouts.
Has this come any closer to being discovered?

They’re getting close, but it’s not easy to get the right number of neutrons.

From http://en.wikipedia.org/wiki/Island_of_stability
Wikipedia said:

The island of stability in nuclear physics describes a set of as-yet undiscovered isotopes of transuranium elements which are theorized to be much more stable than others. Specifically, they are expected to have radioactive decay half-lives of at least minutes or days as compared to seconds, with some expecting half-lives of millions of years.

The manufacture of nuclei on the island of stability proves to be very difficult because the nuclei available as starting materials do not deliver the necessary sum of neutrons.

Has this all been dealt with?

dv said:

Has this all been dealt with?

I think so. Purps seems happy enough…