1. + I. Section 1 Organizing the Elements

2. + A. Mendeleev the Detective 1. Made observations to help make a pattern in the elements 2. Some have similar physical and chemical characteristics 3. Wrote facts about each element on separate cards 4. Atomic mass- the average mass of one atom of the element 5. Bonding power- refers to the number of chemical bonds the element can form

3. + B. The First Periodic Table 1. Noticed the patterns appeared when the element were arranged in order of increasing atomic mass 2. Did not produce a perfect table 3. Left spaces to be filled in with elements that were not discovered yet 4. Periodic Table- the properties of the elements repeat in each row

4. + C. The Periodic Table and the Atom 1. Inside the atom nucleus- the core 2. Inside the nucleus are protons and neutrons 3. Outside are electrons 4. Atomic Mass Unit- measure particles in atoms 5. Protons- Positive 6. Electrons- Negative 7. Neutrons- Neutral

5. + C. The Periodic Table and the Atom 8. Atomic Number- number of protons in the nucleus 9. This identifies the element and is unique, never changes 10. Neutrons can change 11. Today’s periodic table contains more than 100 elements and is arranged by atomic number

6. + D. Reading the Periodic Table 1. Each square includes the atomic number, chemical symbol, name, and atomic mass 2. Inside first is the atomic number 3. Below is the chemical symbol- one or two letters 4. Atomic Mass is last- average mass of the elements atoms 5. Elements are arranged by properties 6. Group- column (families) share properties (18) 7. Periods- horizontal rows- do not share properties (7)

7. + E. Why the Table Works 1. Valence electrons- outside the nucleus- involved in sharing or transfer 2. Valence electrons increases from left to right 3. The elements in each group of the periodic table have the same number and arrangement of valence electrons