Electrons on the third energy level Electrons on the second energy level Electrons on the first energy level (the lowest)
Nucleus containing 15 protons and 16 neutrons
Fig. 6 A Bohr diagram of an atom of phosphorus. Activity Bohr models
1. Collect 20 index cards. 2. Using one card for each element, on one side write the name, symbol, atomic number and mass number of one of the first 20 elements listed on the Periodic Table. The atomic number is the upper number on each card and the mass number is the number at the bottom.
Sodium
11 Na 23
3. On the other side of each index card, draw a Bohr model for the atom of the element showing how the electrons are arranged, as drawn in Fig. 7.
4. Make a separate card for each of the first 20 elements on the Periodic Table. Keep the cards because you will use them again in Chapter 23.
Questions 1. For most atoms, how many times bigger is the mass number than the atomic number?
2. Which atoms follow the pattern you noticed in question 1 exactly?
3. Which atoms have a full outer shell, i.e. the next electron would have to go into a new energy level?
242
4. Which atoms have just one electron in their outer shell? 5. Which atoms need one more electron to have a full outer shell?
