2.  An arrangement of elements in which the elements are separated based on properties

3.  The atomic number of every element represents the number of protons in the nucleus of an atom of that element.

4.  The total number of protons and neutrons in an atom. Number of neutrons = mass number – atomic number

5. http://www.google.com/imgres?imgurl=http://www.hibbing.edu/chem/V.08/isotope_symbols_1.jpg&imgrefurl=http://www.rapidgraphs.com/qwr.php%3Fq%3Disotope- notation&usg=__12aXBa5PuDqU9mdbBqV92mGRrt0=&h=344&w=514&sz=40&hl=en&start=18&zoom=1&tbnid=fj4qDT6dfXQW2M:&tbnh=105&tbnw=157&ei=9lZcTYD5O5GSgQfB44SmDQ&prev=/images%3Fq%3 Dshorthand%2Bnotation%2Bfor%2Bchemical%2Bsymbols%26um%3D1%26hl%3Den%26rlz%3D1T4ADRA_enUS418US418%26biw%3D1259%26bih%3D560%26tbs%3Disch:1&um=1&itbs=1&iact=rc&dur=445&oei= 71ZcTZmxJoHegQenwcD-DQ&page=2&ndsp=21&ved=1t:429,r:12,s:18&tx=99&ty=18 Chemical Symbol Shorthand Notation

6.  Electrons in an atom are equal to the number of protons.

7.  The nucleus is made of p + n  2 protons are close together there is a strong attraction  Nuclear Force

8.  Atoms (of the same element) that have the same number of protons but a different number of neutrons. Do Isotopes have different mass numbers?

9.  Hydrogen  Hydrogen-1 (Hydrogen)  Hydrogen-2 (Deuterium)  Used as a moderator in nuclear reactors  Hydrogen-3 (Tritium)  Used in the production of Hydrogen bombs

10.  There are 3 isotopes of Oxygen. Oxygen-16, Oxygen-17 and Oxygen 18. Write each in shorthand notation.  There are 3 isotopes of Chromium. Chromium- 50, Chromium-52 and Chromium-53. How many neutrons are in each isotope?

11.  One twelfth of the mass of a carbon-12 atom

12.  Calculate a weighted average  Not each isotope is as common as the next  You need to know the mass of each isotope and its natural abundance.