1. The Periodic Table Arranging the Elements

2. Mendeleev’s Periodic Table 1860’s: Mendeleev ordered elements by atomic mass Predicted properties of unknown elements based on properties of surrounding elements But some elements were still out of place—he thought his calculations were wrong

3. What element is it? Mendeleev’s Predictions Actual Properties Atomic Mass 72 Density5.5g/cm 3 AppearanceDark gray metal Melting Point High melting pt 72.6 5.3g/cm 3 Gray metal 937 C Germanium!

4. Proton Discovered 1914—Proton discovered and understood British scientist Henry Moseley arranged elements based on increasing atomic number – this made more sense.

5. Group = Column

6. Period = Row

7. Finding Your Way Around the P.T. Period = row (across) Period = row (across) Group = column (down) Group = column (down) Like coordinates on a grid (Mg is in Period 3, Group 2) Like coordinates on a grid (Mg is in Period 3, Group 2)

8. Actual Shape of the Periodic Table

9. Periodicity Element properties show “periodicity”—regular, repeating pattern Element properties show “periodicity”—regular, repeating pattern Since 1914 more elements have been discovered Since 1914 more elements have been discovered All follow the periodic law: chemical and physical properties of elements are periodic functions of their atomic number All follow the periodic law: chemical and physical properties of elements are periodic functions of their atomic number

10. Periodicity of Density

11. Trends Trend = pattern Left to right trends? Up and down trends?

12. PT Trends What are some trends in the PT that you have already noticed? What are some trends in the PT that you have already noticed?

13. Metallic Character

14. Reactivity Reactivity (how intensely an element reacts with other substances) Reactivity (how intensely an element reacts with other substances) Elements react by taking, giving, or sharing electrons Elements react by taking, giving, or sharing electrons

15. Melting Point

16. Density Metals: basically _______ down the group Non-metals: basically ________ down the group

17. Atomic Radius Trend across a period? Trend across a period? Trend down a group? Trend down a group?

19. Spiral Periodic Table