1. Building Atoms

2. The Periodic Table Will Help You! The PTE is an arrangement of the elements into groups that have similar properties. The horizontal rows are periods. The columns are groups or families.

3. A closer look Each square looks like this: O 8 15.999 Oxygen Atomic Number = Protons OR Electrons Average atomic mass Symbol

4. Drawing the nucleus Draw the nucleus of an oxygen-16 atom: O 8 15.999 Oxygen + + + + + + + + We often replace the picture with: 8p/8n Protons = 8 Neutrons = 16 - 8 = 8

5. What about the electrons? The electrons will go on orbits (energy levels): 8p/8n O 8 15.999 Oxygen Atomic Number = Protons OR Electrons

6. Find the element in the PTE 1 orbit 2 orbits 3 orbits 4 orbits 5 orbits 6 orbits Draw the correct number of orbits. O

7. let’s put the electrons in 8p/8n Rules! The first orbit holds up to 2 electrons. The second orbit holds up to 8 electrons. The order you put them in matters.

8. In general 12 3 4 5 6 7 8 9 101112131415161718 Rules! The 1st orbit holds up to 2 electrons. The 2 nd orbit holds up to 8 electrons. The 3 rd orbit holds up to 8 electrons The 4 th & 5 th each hold up to 18 electrons

9. Lets try Carbon! Draw a carbon-12 atom How many orbits? C 6 12.011 Carbon 2 6p/6n

10. Phosphorus Draw a phosphorus-31 atom How many orbits? 15p/16n 3

11. Valence Electrons Valence electrons are electrons in the outermost orbit of an atom. This carbon atom has 4 valence electrons. The inside orbit is filled. 6p/6n

12. Another way You can also figure out how many valence electrons are in an atom by looking at your periodic table: IGNORE THESE GUYS! 1 Valence electron 2 Valence electrons 3 Valence electrons4 Valence electrons5 Valence electrons6 Valence electrons7 Valence electrons 8 Valence electrons 2 Helium is a special exception- it has only 2!