1. The Periodic Table

2. Objective You will be able to discuss the contributions of Mendeleev, Moseley, and Seaborg in the development of the periodic table.

3. The Periodic Table Dmitri Mendeleev (1869): published first periodic table.

4. arranged by increasing atomic mass grouped by similar properties predicted the existence and properties of unknown elements (Ga, Ge, Hf) Mendeleev’s Periodic Table

5. Mendeleev’s Predictions Property Prediction for ekasilicon Actual for Ge Atomic mass 72 amu 72.59 amu Density5.5 g/cm 3 5.32 g/cm 3 Formula of oxide EsO 2 GeO 2 Formula of chloride EsCl 4 GeCl 4 Predicted in 1871; Ge was discovered in 1886.

6. Is the atomic mass of Tellurium (Te) incorrect? Mendeleev’s Question

7. Henry Moseley Henry Moseley (1911): each element has different # of p +. The table should be arranged by atomic number, not atomic mass. Moseley was killed in Turkey during WWI.

8. The Modern Table Glenn Seaborg arranged our modern table (d-block and f-block).

9. Objectives Know the periodic law. Explain how atomic radius is measured. Understand, identify, and discuss the trends on the periodic table for atomic radius and for electronegativity.

10. Periodic Law periodic law: the properties of the elements repeat periodically “periodicity”

11. Atomic Radius It is difficult to measure atomic size (no definite edge). atomic radius: ½ the distance between the nuclei of two bonded atoms

12. Atomic Radius Trends group trend (down a column): radius increases because new energy levels period trend (across a row): radius decreases because electrons are in the same “shell” but added protons pull inward on the shell.

13. Electronegativity electronegativity: the tendency of an atom to attract electrons when it is bonded to another atom The nucleus of a small atom pulls strongly on the outer electrons of a large atom + + +

14. Electronegativity Trends group trend: electronegativity decreases (atoms get larger) period trend: electronegativity increases (atoms get smaller)

15. Objectives You will be able to compare the reactivity of elements. You will be able to explain why specific elements are either reactive or unreactive.

16. Metals and Non-Metals Metals tend to lose their outer “valence” electrons because they are large (low electronegativity). Non-metals tend to attract electrons because they are small (high electronegativity).

17. Reactivity Trends same group = similar properties (like reactivity) = similar e- configurations metals: largest, with fewest valence e- are most reactive non-metals: smallest, with most valence e- are most reactive (excluding noble gases—outer shell is full) Which is the most reactive? Ca, Cu, Rb, Na S, Cl, Br, C, Ne

18. Reaction Clips Alkali Metal Reactions Sodium and Chlorine Reaction Fluorine Reactions