1. The Periodic Table
History of the Table

2. Compacted table

3. Full Extended Table

4. Origin By 1850, over 50 different substances had been discovered.
Scientists needed a way to organize these substances into some logical order.
By the mid 1800s, scientists had already discovered over 50 pure substances.
At the time, they did not know about atoms, but they knew these substances were made up of only one type of particle. Today we call them elements.

5. Early Concepts Johann Doebereiner John Newlands
Johann Doebereiner – noticed a pattern that existed between different sets of three elements. He saw that these elements had similar physical and chemical properties. He also found that the average atomic mass of the larger and smaller elements yielded the atomic mass of the middle element. These were called “Doebereiner’s Triads.” There are about eleven such sets in our current periodic table. This pattern, however, did not exist for all elements.
John Newlands – noticed a repeating pattern on every eighth element. Like Doebereiner, he saw that these elements had similar physical and chemical properties. His idea of the repeating pattern became known as “Newland’s Octaves” or the “Law of Octaves.” This pattern worked more often that Doebereiner’s Triads but still was not the solution to the problem.
Johann Doebereiner
John Newlands

6. Dmitri Mendeleev
Mendeleev, Dmitri ( ): Russian chemist arranged the 63 known elements into a Periodic Table (1868) based on Atomic Mass. He predicted the existence and properties of new elements and pointed out accepted atomic weights that were in error.
Mendeleev provided for variance from strict atomic weight order, left space (10 gaps) for new elements, and predicted three (gallium, germanium and scandium) elements that were discovered within 15 years. His table did not include any of the Noble Gases, however, which had not yet been discovered.
(1834 – 1907)

7. Dmitri Mendeleev Organized elements according to their atomic mass.
Left space (10 gaps) for new elements.
Predicted the existence of three undiscovered elements.
Mendeleev, Dmitri ( ): Russian chemist arranged the 63 known elements into a Periodic Table (1868) based on Atomic Mass. He predicted the existence and properties of new elements and pointed out accepted atomic weights that were in error.
Mendeleev provided for variance from strict atomic weight order, left space (10 gaps) for new elements, and predicted three (gallium, germanium and scandium) elements that were discovered within 15 years. His table did not include any of the Noble Gases, however, which had not yet been discovered.

8. Dmitri Mendeleev

9. Henry Moseley
Moseley, Henry ( ): A British chemist who developed the application of X-ray spectra to study atomic structure; his discoveries resulted in a more accurate positioning of elements in the Periodic Table (1913) by closer determination of atomic numbers.
Henry Moseley used x-rays to analyze the elements and order them by the number of protons (or atomic number).
When atoms were arranged according to increasing atomic number, the few problems with Mendeleev's periodic table had disappeared. Because of Moseley's work, the modern periodic table is based on the atomic numbers of the elements.
(1887 – 1915)

10. Henry Moseley Organized elements according to their atomic number.
Solved problems found in Mendeleev’s periodic table.
Credited with final format of today’s periodic table.
Moseley, Henry ( ): A British chemist who developed the application of X-ray spectra to study atomic structure; his discoveries resulted in a more accurate positioning of elements in the Periodic Table (1913) by closer determination of atomic numbers.
Henry Moseley used x-rays to analyze the elements and order them by the number of protons (or atomic number).
When atoms were arranged according to increasing atomic number, the few problems with Mendeleev's periodic table had disappeared. Because of Moseley's work, the modern periodic table is based on the atomic numbers of the elements.

11. Vocabulary atomic mass atomic number element Mendeleev Moseley
periodic