I haven't taken a science course in four years now and I'm trying to recall some very basic concepts.

What defines an element's atomic number - is it the number of protons, neutrons, or electrons present in an atom of the element?

The reason I ask is because I know electrons can be gained and lost (producing ions) - I'm wondering if this changes the atom's atomic number (and thus the element). Also, can protons or neutrons be gained or lost from the nucleus of an atom or are they constant in the atom?

Thanks!

http://www.pbs.org/wgbh/aso/tryit/atom/

http://www.sciam.com/askexpert/physics/physics46/physics46.html

Might want to check out this site and play around some with the periodic table:

http://www.webelements.com/

Has a lot of neat features and a ton of info.

Welcome to Sciforums

Take care

So the number of protons in the atom defines an element's atomic number. Okay. That means the atomic number won't change when the atom loses or gains electrons (becomes an ion).

But the atomic number will change during positron emission (ejection of a positive electron, or positron, from the nucleus), since the process results in a proton turning into a neutron. The atomic number will decrease by one and so it will be a "new" element.

The atomic number of an atom will also change during "K capture," when the nucleus captures an electron from the K shell and the captured electron converts a proton into a neutron.

Aside from these two cases, an atom will always stay of the same element, right?

Oh, I missed two. Beta emission decreases the number of neutrons by 1 and increases the number of protons by 1. Alpha emission lowers both the proton and neutron count by two?! Is this right?

Hi Weitzel,

Beta emission can occur in two ways: a proton can be converted into a neutron, but the other way around is also possible (neutron -> proton). These decay mechanisms are known as Beta+ and Beta- decay (unfortunately I cannot remember at the moment which one was which ;)).

Alpha emission is when an alpha particle ( = 2He core, 2 protons and 2 neutrons) is ejected from the nucleus. This indeed reduces the proton and neutron number by two.

At the moment, I think these are the only natural occuring mechanisms for changing the nucleus type. However, sooner or later it is always possible that other mechanisms are discovered aswel.

Bye!

Crisp