Atoms
Atoms ... they are the heart of it all! So here are a few things to remember about atoms. Atoms are made of smaller parts called subatomic particles: protons, electrons, and neutrons.

Subatomic particles are important because they give us information about some of the behaviors of atoms. So we need to know how we can figure out the number of each of the subatomic particles. Happily, it is easy!!
Each element is represented on the periodic table with some really important information readily available at all times for your use. The atomic number, unique to each element tells you the number of protons that a particular atom has AND the number of electrons the atom has.

In the examples above:

 Carbon Nitrogen Iron Atomic Number: 6 8 26 Protons: 6 8 26 Electrons: 6 8 26

Nice and easy. No math, no calculation, just remembering to look it up on the Periodic Table.

The number of neutrons is a bit harder to come by. That is because, as it turns out, the number of neutrons is not used as often, and is a bit more complex to understand, so it is NOT included on the periodic table. And, notice that I haven’t mentioned anything about the bigger, second number on the Periodic table. That’s the atomic mass.

ISOTOPES

As it turns out, the atoms of an element are not exactly alike. Although they are all alike in many ways, atoms of a particular element, like carbon atoms, vary in mass. Carbon atoms come in three different masses. These three different forms of carbon are called isotopes. The symbols below show how the three isotopes of carbon can be written.

The isotopes can also be written as C-14, C-13, and C-12.

Isotopes vary in mass because they have different number of neutrons in the nucleus.

Protons + Neutrons = Mass Number

6p+ + 6no = 12, the mass number of the first isotope of carbon
6p+ + 7no = 13, the mass number of the second isotope of carbon
6p+ + 8no = 14, the mass number of the third isotope of carbon

Notice that to know the number of neutrons, you have to be given the isotope information either in the form  or C-14.

Examples
You use the information in the given symbols to figure out the number of protons, electrons and neutrons as well as the atomic number of each isotope.

 Isotope Symbol Fe-59 Fe-58 N-15 Na-23 Ag-108

 Isotope Symbol Mg-25 Cr-52 Sr-88 Br-79 P-33 Pb-207 C-14

G Waller

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