Here is a question from a class member, along with my answer. Also, take a look at Joy's message dated 4/15 - she found help on another website.

QUESTION: I am trying to complete homework 2, and I am having difficulties with question 8 (the fill in the chart)...Is there a chart, or learning method to utilize when trying to figure the number of electrons, protons, and neutrons for elements?

ANSWER:Here is something that might help - it's sort of a "flow sheet" to your questions:

1) Protons are the main "identity" - the name of the element and the atomic number (proton number) always go together.

So, for example, the name chlorine and the atomic number 17 always go together, and that means that chlorine always has 17 protons.

2) Next to consider is the charge relationship. This always involves the protons AND the electrons, since they are the charged particles. Once the proton number (atomic number) is established, the number of electrons can be found by asking whether you are dealing with an ATOM or and ION.

If it's an ATOM, it's neutral, so the number of electrons has to EQUAL the number of protons. For example, a chlorine ATOM would have 17 electrons.

If it's an ION, the number of electrons will no longer equal the number of protons. In ordinary chemical change, this happens because of electrons "coming and going", or, to say it another way, electrons being "gained or lost".

An anion is a result of electrons being gained. The result is that there will be MORE electrons than protons, so there will be a surplus of NEGATIVE charge, and it will be an ANION. For example, a chloride ION (an ANION) has 1 extra electron, and its charge is -1. That's because there are 17 + (protons) and 18 - electrons. A sulfide ion has two extra electrons, and its charge is -2 (16+ and 18-).

A cation is a result of electrons being lost. The result is that there will be FEWER electrons than protons, so there will be a surplus of POSITIVE charge, and it will be a CATION. For example, a potassium ION (a CATION) has lost one electron, and its charge is +1. That's because there are 19 + (protons) and 18 - electrons. A calcium ion has lost two electrons, and its charge is +2 (20+ and 18-).

The last thing to consider is the weight (mass) relationship. Compared to protons and neutrons, electrons have hardly any mass, so you can ignore them for this. The weight on the chart (atomic weight or atomic mass) when rounded to the nearest whole number, is the sum of protons and neutrons. (protons + neutrons = weight) Since the proton number is set by the name of the element, you can subtract that from the weight to get the number of neutrons (weight - protons = neutrons).

Hope this helps.

sg