Chapter 4, Section 2 Pages 131-137

1. Chapter 4, Section 2Pages 131-137 Organizing the Elements

2. The Periodic Table • An arrangement of elements showing the repeating pattern of their properties. • The properties of an element can be predicted from its location on the periodic table. • Periodic means “in a regular, repeated pattern.”

3. How the Periodic Table Began • By 1869, a total of 69 elements had been discovered. Most of these were solid metals, a few were gases and two were liquids. • Scientists, including Mendeleev, noticed that certain elements had similar chemical and physical characteristics. (figures 11 & 12, pg. 132)

4. Mendeleev’s Periodic Table • Mendeleev studied these characteristics by writing each elements melting point, density and color on individual cards, including the elements atomic mass, and comparing them to each other. • He noticed a pattern of properties appeared when he arranged them in order of increasing atomic mass.

5. Mendeleev’s Periodic Table • During the construction of his periodic table Mendeleev noticed that organizing the elements in the order of their atomic mass didn’t always group similar elements together. • This led him to move a few elements in groups with similar properties. • Mendeleev published his periodic table in 1869, leaving three blank spaces filled with question marks for elements he predicted would be discovered going by the properties of the surrounding elements. (fig. 13, pg. 133)

6. Within 16 years chemists discovered the three missing elements with properties similar to those which Mendeleev had previously predicted.

7. The Modern Periodic Table • The periodic table changed as scientists discovered new elements and learned more about atomic structure. • It is organized differently from Mendeleev’s table and has more than 100 elements. (fig. 14, pg. 134-135)

8. Periods • The horizontal rows of the periodic table that contain a series of different elements, which have properties that change in pattern from left to right. • Metals are on the left with the most reactive metals on the far left. • Nonmetals are located on the right with the most reactive inert gases on the far right. • Semimetals are found between metals and nonmetals.

9. Groups • The vertical columns of the periodic table that consists of elements with similar characteristics. • Group 1 elements react violently with water, while group 2 elements react slowly or not at all. • Group 17 elements react violently with group 1 elements. • Group 18 elements rarely react at all.

10. Classes of Elements • Starting at the upper left of the periodic table with Hydrogen (H), notice that the atomic numbers increase from left to right. • Notice also that the periodic table is color coded. Each color coded region corresponds to a different class of elements- • Metals, semimetals, nonmetals, and inert gases.

11. Reading the Data • Each square in the periodic table lists four pieces of information: • An element’s atomic number, chemical symbol, name, and atomic mass.