# Science question! Periodic Table of Elements

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DDs science book today threw mom for a loop. It introduces the periodic table of elements but doesn't tell you how to find one of the items you are supposed to figure out. We think we figured it out but even with google, I couldn't find the answer. If DH were here, he'd know but he's gone until late tonight. I knew someone here would know. They want us to find the number of neutrons. Do you take the atomic mass and subtract all the #s on the right (# of electrons in each shell)?

2. ### fletchsmMember

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Well it looks like this page is saying to subtract the Atomic number from the atomic mass and you have your neutrons. And since the atomic number is the number of protons and you have to have the same number of protons as electrons. :stars:

http://education.jlab.org/qa/pen_number.html

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Round up the atomic weight to a whole number (the mass number) and then subtract the atomic number.

4. ### CatsPawWho...me?

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atoms always have the same number of protons as neutrons. The atomic number is the number of protons and the number of neutrons.

He atomic number is 2= two protons and two neutrons.

5. ### gramsfiber crone

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Bingo! Thanks! I wrote it right into the book since I have another child doing this next year. Must be DH was home when we did this last year I didn't remember.

7. ### CatsPawWho...me?

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Well, what I said technically is correct. Take carbon. Carbon has an atomic NUMBER of 12. It has 12 protons and 12 neutrons.

Now these things don't always have the same number of anything, but then you get into other things.

If you increase the number of neutrons, say, in carbon, you can get C-13 or C-14, but then you have an isotope. But isotopes generally want to give off those extra neutrons over time as radioactivity and would tend towards the original number of 12 protons and 12 neutrons.

Technically speaking an atom has the same number of electrons and protons, but commonly don't. But then they're called ions....well then you get into covalent and electrovalent bonding like in Na+ and Cl-, or K+ or Ca2+ floating around in your muscles and stuff.

Google "structure of an atom" and there are some real good sites about it.

To me it's just easier to look at the atomic number.

8. ### CatsPawWho...me?

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o.k....correction carbon 6 protons 6 neutrons...had twelves on the brain.....C 13 would have 6 protons and 7 neutrons......etc. etc.

9. ### JennWell-Known MemberSupporter

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the atoms with different number neutrons are called isotopes. mistletoad is correct- recall electrons are virtually weightless.

10. ### menollyrjJoySupporter

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I just finished teaching a unit on this, and it sounds like y'all have the right of it.

Atomic # is the whole number listed with each element. Carbon is 6, oxygen is 8, hydrogen is 1, etc... There is also a decimal number listed. That is atomic mass/atomic weight/molar mass/mass number (all names are correct). If you round the decimal to the nearest whole number (some round up and some round down), the resulting number is equal to protons plus neutrons. To find # of neutrons, subtract the atomic # from the atomic mass. The atomic mass on the periodic table is a weighted average, and is generally equal (when rounded) to the mass of the most common isotope. Isotopes have the same number of protons (since that is what determines the identity of the element), but a different number of neutrons. When an element is written with a number behind it, as with C-14 (carbon-14), the number at the end is the mass number for the particular isotope. So, for C-14, there are 6 protons (because that is the atomic number) and 8 neutrons (or 14 minus 6).

What Catspaw said about protons & electrons is also correct. A NEUTRAL atom (no charge) has the same number of protons and electrons. This should make sense because protons are positively charged, and electrons are negatively charged. In order for the atom to be electrically neutral, there has to be just as many negatives as positives (or just as many electrons as protons). However, when an atom has more or less electrons than protons, the atom can have charge.

Protons determine identity. Hydrogen always has 1 proton. If it has 2 protons, it isn't hydrogen any more, but helium instead. Neutrons determine isotope. Electrons determine charge.

-Joy

11. ### CatsPawWho...me?

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In testing myself on all this, what I found out and didn't know was that Hydrogen doesn't have a neutron.....cool.