Ions and Isotopes Notes - DOC by uda13689

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									                                   Ions and Isotopes Notes

An ion is an atom of an element that has gained or lost electrons.

Positive ions (cations) lose electrons.

Negative ions (anions) gain electrons.



   Group Number and Name                        Valence Electrons               Oxidation Numbers
        1—Alkali metals                                 1                               +1
   2—Alkaline Earth Metals                              2                               +2
       13—Boron Group                                   3                               +3
      14—Carbon Group                                   4                              +/- 4
     15—Nitrogen Group                                  5                               -3
      16—Oxygen Group                                   6                               -2
         17—Halogens                                    7                               -1
       18—Noble Gases                     8 (filled outer energy level)                none


Atoms of elements on the periodic table are neutral because the number of protons and electrons in an
atom are the same. So, the positive and negative charges cancel each other out.

        Example:         Nitrogen has an atomic number of 7. This means it has 7 protons (+ charges)
and 7 electrons (-- charges).



In an ion, this is not the case. See the Bohr Model below of a Sodium (Na) atom.




                     11p
                                                         VALENCE ELECTRON
                     12n




                                          Notice that there is one electron in the outer energy level. This
is the valence electron. In an ion, the valence electrons are either gained or lost when chemical bonding
occurs, such as during ionic or covalent bonding. In this case, the electron is lost in order to achieve a
                                                                                         +1
stable atom configuration ( or full outer energy level). So, the new ion formed is Na , and the
resulting ion now has a positive one charge or oxidation number.
                               Ions and Isotopes Notes

See the table on page one of the notes to see which groups or families form what ions.



Another way to show the valence electrons of an atom is to use the Lewis Structure for that
atom. Instead of drawing out the whole Bohr Model, you can simply write the element’s
symbol and then show the valence electrons as dots around the symbol.

Example:

                                  Na


Isotopes are atoms of the same element, that have the same number of protons, but different
numbers of neutrons. This in turn changes the mass number for that isotope.

Think of isotopes as being different varieties of the same thing. For example, you have shoes in
your closet. You may have house shoes, flip-flops, dress shoes, sandals, tennis shoes, and
cowboy boots. They are all shoes, just different kinds of shoes. The same idea applies to
isotopes. They are atoms of the same element, but because they have different numbers of
neutrons, they have some different properties.

Some elements have just a few isotopes, while others have as many as 50 or more isotopes of
the same element.

The correct way to name or label an isotope is to put the element name or symbol, then a
hyphen, and then the mass number for that particular isotope.

Example:

                                  Copper - 63 and Copper – 65

                                              Or

                                     Cu – 63 and Cu—65

To find the mass number, you take the number of protons + the number of neutrons. Mass
number is used when referring to an individual isotope. To find the Atomic Mass, you have to
take all of the masses of the isotopes, multiply each one by the percentage of time they are
found in nature. Then, take the average of all the isotopes. This is the Average Atomic Mass
and is the decimal number found on the periodic table.
                               Ions and Isotopes Notes

Example:

Copper -63 is found in nature 69% of the time. Copper-65 is found in nature 31% of the time.

So,

(63 x 0.69) = 43.47 amu

(65 x 0.31) = 20.15 amu

43.47 + 20.15 = 63.62 amu

This is the average atomic mass that you find on the periodic table for Copper.



Comparing Ions and Isotopes:




                                                       Isotopes-
                                                       different
           Ions-electrons                # of
                                                     numbers of
            are gained or                Protons
                                         does not
                                                    neutrons and
                 lost                    change
                                                    different mass
                                                       numbers

								
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