What would the nucleus look like?

Question

Ok, I have a summer assignment that's due on the first day of school. I'm supposed to make models. Scandium has 21 protons. Does this mean the nucleus has 21 protons and 21 electrons? Or does it mean that there's 21 all together?

Answer 1

The electrons aren't in the nucleus; they "orbit" around it. (Orbit is in scare quotes here for reasons that you'll eventually see in quantum mechanics, hopefully.)

But yes, scandium has an atomic number of 21, which means 21 protons. As long as we're not talking about an *ion*, and we're talking about scandium *atoms*, then there's no net charge, and scandium must therefore have 21 electrons as well. (Electrons and protons have the same "size" of charge, but opposite polarity. So you need 21 electrons to balance out the 21 protons, to get 0 charge total.)

You might be thinking about neutrons, which are also in the nucleus and have almost the same mass as that of a proton. (Electrons have almost no mass at all, by comparison.)

The atomic weight of scandium is 45, which means that it has 45 nucleons. 21 of them are protons, which means 24 of them must be neutrons.

Answer 2

Naturally occurring scandium is composed of 1 stable isotope that has 21 protons and 24 neutrons in the nucleus and 21 electrons not in the center.

Answer 3

With one exception, all atom nuclei have both protons and neutrons.  The one exception is hydrogen, which has but one proton, no neutron.  So when you talked about scandium with 21 protons, you also have to add in its neutrons to the core.

That's it proton and neutrons (discounting neutrinos which are rarely included in the nuclei models).  There are no electrons in the core in the classical model, even though guantum physics claims some small probability that an electron could be found in the nucleus.

The electrons, in the classic model, would all lie outside the core, forming a kind of layerd cloud around the nucleus.  Each layer would represent the energy level of the included electrons, The number of electrons in each layer depends on the layer; for example, there are two in the innermost layer and 8 in the next one out from it.  

Unless the atom is an ion, the total number of electrons is the same as the total number of protons in any atom.  That's why there are 21 protons and 21 electrons...the atom is not an ion.