Trends & the Periodic Table

1. Trends & the Periodic Table Ionization Energy, Electronegativity, & Metallic Reactivity

2. Trends • More than 20 properties change in a predictable way based on location of element in P.T. • Include: density, melting point, atomic radius, ionization energy, electronegativity

3. previous | index | next Size  as you go  and size  as you go  Source: Conceptual Chemistry by John Suchocki

4. What’s the trend for effective nuclear charge? • Effective Nuclear Charge = Atomic # - Inner Shell Electrons. • Increases as you go across a row. • Stays constant as you go down a column.

5. Ionization Energy • Amount of energy required to remove an electron from a gas-phase atom. • First ionization energy or ionization energy = energy required to remove most loosely held valence electron. • Na(g) + energy  Na+1(g) + 1e- • (This is an endothermic process!)

6. Trends in ionization energy • What do you think happens to the ionization energy as you go down a column of the periodic table? Li vs. Cs? • As you go across a row? Li vs. F?

7.  previous | index | next Valence electrons in both atoms feel an effective nuclear charge of +1, but the Cs valence electron is a lot farther away from the nucleus. The electrostatic attraction will be much weaker. So it’s easier to steal the electron away from Cs. Source: Conceptual Chemistry by John Suchocki

8.  previous | index | next It’s easier to steal an electron from the Li than the Ne. Li has a smaller effective nuclear charge and the valence electron is a little farther away from the nucleus. Li has less “proton pulling power” than Ne. Source: Conceptual Chemistry by John Suchocki

9. Trends in ionization energy • Ionization energy decreases as you go down a column – it gets easier & easier to remove the valence electron. • Ionization energy increases as you go across a row – it gets more difficult to remove the valence electron.

10. Periodic properties: Graph shows a repetitive pattern. Doesn’t have to be a straight line.

11. Electronegativity • Relative ability of an atom to attract electrons in a bond. • The noble gases tend not to form bonds, so they don’t have electronegativities. • Unit = Pauling. • Fluorine is the most electronegative element at 4.0.

12. Formation of a covalent bond The green atom is grabbing more than its fair share of the electron cloud. It is more electronegative. Polar Covalant Bond Nonpolar Covalent Bond

13. Trends in electronegativity • Related to “proton pulling power.” • Pulling power depends on size of charge and distance from electrons. • What’s the trend for effective nuclear charge? • What’s the trend for atomic size? Increases across. Constant down. Decreases across. Increases down.

14. Trends in electronegativity • Related to “proton pulling power.” • Increases as you go across a row. • Decreases as you go down a column. • Remember: F is the most electronegative element!

16. Reactivity of Metals • Metals are losers! • We judge the reactivity of metals by how easily theygive upelectrons. • What property do we look at to assess how easily metals give up electrons? Ionization energy: the smaller it is, the easier the metal loses electrons.

17. Reactivity of Metals • The most active metals are Cs and Fr. They have the smallest ionization energy. • For metals, reactivity goes up as ionization energy decreases.

18. Trends for Reactivity of Metals or Metallic Character • Increases as you go down. • Easier to lose electrons! • Decreases as you go across. • Harder to lose electrons! Can you identify the K, Na, and Li in this clip?

19. Reactivity of Non-metals • Non-metals are winners! • We judge the reactivity of non-metals by how easily theygainelectrons. • What property do we look at to assess how easily nonmetals gain electrons? Electronegativity

20. Reactivity of Non-metals • The most active non-metal is fluorine. • F has the largest electronegativity. • For non-metals, reactivity increases as electronegativity increases.

21. Trend for Reactivity of Non-metals:Depends on the “proton pulling power” • Increases as you go across. • Decreases as you go down. (Shielded by more inner-shell electrons.)

22. Allotrope • Different forms of an element in the same phase. Have different structures and properties. • O2 and O3 - both gas phase • Graphite, diamond, buckey balls – all solid phase carbon.

23. C60

24. Graphite and Diamond