2.  Nucleus contains most of the mass of the atom ◦ Protons and neutrons are far more massive than electrons ◦ Mass of a proton or neutron is approximately 1.6726 X 10 -24 ◦ This mass of a proton is about 1,836 times the mass of an electron

3.  Not measured in normal units  Amu – atomic mass unit

4.  Each element can be described by the number of protons it has  The number of protons in an atom is known as its atomic number  What is the atomic number for the following atoms??? ◦ Nitrogen (N), Oxygen (O), Hydrogen (H), Boron (B), Silver (Ag), Antimony (Sb)

5.  If we know one of the following we then know also the other two: ◦ Atomic number ◦ Name of the element ◦ Number of protons

6.  The mass number of an atom is the sum of the number of protons and the number of neutrons in the nucleus of an atom.  Mass number

7.  By using the atomic number and the mass number (which is also called the atomic mass) you can find how many neutrons are in an atom of an element.  Number of neutrons = mass number – atomic number

8.  Some elements can be found with differing number of neutrons  Isotopes – atoms of the same element that have different numbers of neutrons  Some elements such as Carbon have different Isotopes there is a Carbon-12 isotope and a Carbon-14 isotope… which means that Carbon-12 isotope has 12 neutrons and Carbon-14 isotope has 14 neutrons

9.  Decimal places are found in the mass number… this is because the mass number is the average atomic mass of an element  Average atomic mass – the weighted-average mass of the mixture of its isotopes  For example ◦ If we had 5 boron atoms randomly found in nature  4 Boron-11 and 1 Boron-10  How would we find the average atomic mass of these atoms??? ◦ The average atomic mass of boron is close to the mass of its most abundant isotope, boron-11

10.  On a blank sheet of paper please draw a diagram for the nucleus of each of the following: Carbon-12, Carbon- 13, and Carbon-14. And Identify which Carbon Isotope is found more often (hint you can calculate this or it is in your book).  Be sure to put the correct amount of protons and neutrons (using different colors) – also write underneath how many protons and neutrons for each isotope.  Correctly label each isotope and color coordinate your protons and neutrons (place a key in the corner to correctly identify which are protons and which are neutrons).  An example of how to draw a nucleus is Figure 8 on page 515.  At the bottom of the page explain what an isotope is  and reference your drawing.