History of Periodic Table

1. History of Periodic Table

2. 1817, German chemist Dobereiner grouped elements in threes based on chemical properties “Law of Triads” calcium, strontium, and barium lithium, sodium, and potassium chlorine, bromine, and iodine Sulphur, selenium, and tellerium The atomic mass of the second element was almost exactly the average of the atomic weights of the first and third element Johann Dobereiner

3. 1865: British chemist John Newlands organizes the 56 known elements into eleven groups which were based on similar physical properties, listing them in a table determined by atomic weight “Law of octaves” John Newlands

4. 1869, Russian chemist Dmitri Mendeleev organizes the elements by atomic mass Added new rows directly below elements with similar properties Left gaps where elements did not fit the pattern The physical and chemical properties of the elements are periodic functions of their atomic numbers. Dmitri Ivanovich Mendeleev

5. Mendeleev’s Periodic Table • Predicted properties of elements not yet discovered • Some elements do not follow the pattern • Which ones are they? • Ar & K • Ni & Co • Te & I

6. 1911, English scientist Henry Moseley organized elements by increasing atomic number Elements fit into patterns better when organized by increasing nuclear charge, or the number of protons. Moseley’s work let to both the modern definition of the atomic number and the recognition that atomic number, is the basis for the organization of the periodic table. Henry G. Moseley

7. Periodic Law: Mendeleev’s principal of chemical periodicity is known as periodic law When elements are arranged according to their atomic numbers, elements with similar properties appear at regular intervals Using the periodic law, elements can be linked together by their chemical properties. Periodic Law