1. The Lion and the Gazelle Every morning in Africa, a gazelle wakes up. It knows it must run faster than the fastest lion or it will be killed. Every morning a lion wakes up. It knows it must outrun the slowest gazelle or it will starve to death. It doesn't matter whether you are a lion or a gazelle. When the sun comes up, you better start running. -African Proverb

2. Counting the Parts of Atoms Coach Woodruff Earth and Physical Science Building Atoms

3. Atomic Number Atoms of different elements have different numbers of protons. The atomic number of an element is the number of protons in the nucleus of each atom of that element.

4. Atomic Number Atoms of hydrogen have 1 proton; atoms of helium have 2 protons, and so on. The atomic number identifies an element. Since atoms are neutral, an atom will have the same number of protons as electrons.

5. Isotopes Isotopes are atoms of the same element that have different masses. Isotopes will have the same number of protons and electrons, but will differ in the number of neutrons. For example, Hydrogen has 3 isotopes:  Protium- one proton, no neutrons  Deuterium- one proton, one neutron  Tritium- one proton, two neutrons.

6. Mass Number The mass number of an atom is the total number of protons and neutrons in the nucleus of an isotope.

7. Designating Isotopes Only hydrogen has different names for its isotopes. There are two ways we designate isotopes:  Hyphen notation: hydrogen-1, uranium-235  Nuclear symbol: mass # top, atomic # 1 H, 235 U 1 92 We find the number of neutrons by subtracting the atomic number from the mass number- Ex: 235 U  235-92=143 neutrons 92

8. Sample Problem How many protons, neutrons, and electrons are found in an atom of Helium-4?  Protons-2, Neutrons-2, Electrons-2 How many protons, neutrons, and electrons are found in an atom of 120 Sn? 50  Protons-50, Neutrons-70, Electrons-50 Masses of atoms in grams are very small.

9. Check Your Understanding List how many protons, neutrons, and electrons are in each of the following atoms.  Nickel-60  Barium-138  Krypton-86  Nitrogen-14  31 P  201 Hg  42 Ca  184 W 15 80 20 74

10. Build A Bohr Atom First- Determine the Number of Protons, Neutrons and Electrons for your Element. Second- Determine how many energy levels you need for your model. (remember shell 1- 2e-, shell 2- 8e-, shell 3- 8e-, shell 4- 18e-, shell 5- 18e- Third- Fill your shell from inside to outside until you run out of electrons.

11. Now you do it! Practice your Bohr Model Atom Building skills on the Model Practice Worksheet. If you need help raise your hand and I will point you in the right direction.