1) Mendeleev arranged the elements in his periodic table based on increasing atomic mass, with elements of similar properties placed in columns. 2) His table had gaps for elements not yet discovered, but he predicted their properties. When these were later discovered, such as gallium, they matched his predictions, verifying his periodic table. 3) The periodic table is organized so that elements are classified based on atomic structure, with properties repeating periodically from row to row.

1. Warm – Up Is flammability a physical or chemical property? Why? Chemical property because burning a substance is combining with oxygen and creating a new substance What happens to the composition of matter during a physical change? The substance does not change only shape or some other physical change takes place.

2. 3-5 Organizing Elements Objectives Describe how Medeleev arranged the elements in his table. Explain how the predictions helped verify the usefulness of his periodic table.

3. Why do we classify/organize? How are most library books classified? Why is this classification useful? How do Biologist classify living organisms? Domain, Kingdom, Phylum, Class, Order, Genus, Species. Why do we classify/organize? Easier to find and identify.

4. Searching For Order Until 1750, only 17 elements were known. Most identified were metals. In 1789, Lavoisier grouped atoms into 4 types. Metals, nonmetals, gases and earths.

5. John Newlands 1 st & 8 th elements, 2 nd & 9 th had similar properties, and so on. Law of octaves Organized the first 14 “known” elements. Pattern stopped

6. Mendeleev’s Periodic Table In 1860, he used solitaire to help him organize the known 63 elements Wrote element on a card Looked at the elements properties. Lined the cards up in increasing mass. He saw a pattern that repeated. Rearranged to create columns of similar properties. Properties repeat from row to row.

7. Questions What does periodic mean? Occurring at regular intervals.

8. Mendeleev’s Predictions He couldn’t complete his table because of gaps in the elements. Those elements had not been discovered.

9. Other Systems In 1829, Dobereiner proposed a law of triads. It is a group of 3 similar elements. The middle element has properties between the other two. Example Li – 6.941 Na – 22.990 K – 39.098 Average (6.941+39.098)/2 = 23.02

10. Evidence for Mendeleev’s Table He named missing elements after the same group. I.E. Element below Al, he named eka-aluminum. He predicted it would be a soft metal with low melting point and a density of 5.9 g/cm 3 . French chemists actually discovered it in 1875. Gallium (Ga) is a soft metal with 29.7 o C M.P. and a density of 5.91 g/cm 3 .

12. Questions How was Mendeleev’s table organized? Elements are arranged in order of increasing mass. How do the properties repeat? Row to row. New columns are created for each set of similar properties

13. http://education.jlab.org/elementflashcards http://www.webelements.com/ http://pearl1.lanl.gov/periodic/