1. The Periodic Table Chapter 5.1 Notes

2. Organizing the Elements Dmitri Mendeleev was a Russian chemist and one of the first to organize the elements Considered the “father of the periodic table” In 1869, Mendeleev organized the elements in rows based on increasing atomic mass When the chemical properties of the elements repeated, he started a new row All elements in the same column have similar properties

3. Predicting New Elements When Mendeleev was organizing the elements, he found that there were some spots where no known elements fit the pattern Left these spots open with a question mark, predicting that other scientists would discover new elements that fit the pattern and filled in his blanks

4. Predicting New Elements Mendeleev left a space after silicon. Predicted that the missing element would be a gray metal with a high melting point. 1886, germanium was discovered—which has the properties Mendeleev predicted.

5. Changing the Arrangement 40 years later, Henry Moseley arranged the elements by atomic number rather than atomic mass What is the difference between atomic number and atomic mass? This new arrangement fixed some of the problems that Mendeleev had with different elements not quite fitting the pattern he had created The modern periodic table organizes elements by atomic number; there are more than 100 known elements

7. Periodic Trends Each row is called a period 7 periods Elements become less metallic as you go from left to right Properties such as reactivity and conductivity also change Are these physical or chemical properties? Each column is called a group 18 groups Elements in the same group have similar properties