1. Key Concept: Elements make up the periodic table
Ch. 16.2
Key Concept: Elements make up the periodic table

2. I. Elements can be organized by similarities
Atomic Mass
Periodic Table
Mendeleev- Organize elements by chemical/physical properties
Rows- similar chemical properties
Period
Columns- similar physical properties
Family
Group

3. C. Groups & Periods Group- elements listed in a vertical column
Labeled by a # at the top of the column
Sometimes called a family
Period- elements listed in a horizontal row
Properties change in a predictable way from one end of a period to another

4. II. The periodic table organizes the atoms of the elements by properties and atomic number
Reading the Periodic Table
# at the top= atomic number
Chemical Symbol- abbreviation for an element
Name
Atomic Mass- indicates AVERAGE mass of all isotopes of the element
Color of Symbol- (if present) indicates the physical state of the element at room temperature

5. C. Trends
Atoms on the left side form positive ions easily (Group 1 form +1 ions Group 18 forms no + ions). Atoms on the right side form negative ions easily
Atom size decreases as you move to the right of the table. Atom size increases as you move down the table.
Density generally increases from the top of a group to the bottom. Atoms to the right and left are the least dense and the atoms in the middle are the most dense.