The Periodic Table

1. The Periodic Table Periodic Trends

2. Trends in Atomic Size

3. Atomic Radii • We must use an indirect method to measure the diameter of an atom • The atomic radius is one half of the distance between the nuclei of two atoms of the same element when the atoms are joined

4. These distances are measured in picometers 1 pm = 10-12 m

5. Increasing Increasing In general, atomic size increases from top to bottom within a group and decreases from left to right across a period.

6. Another View

7. 1 2 3 7 4 5 6 8 10 9 11 12 13 14 15 16 17 18 20 19

8. Ions • What is the charge on an atom? • An ion is an atom or groups of atoms that has a + or – charge • Ions form when electrons are transferred between atoms

9. Cations Anions & + - Na Cl • Ions with positive charges are cations • These are usually formed by metals • Metals lose one or more electrons • Ions with negative charges are anions • These are usually formed by nonmetals • Nonmetals gain one or more electrons

10. Trends in Ionization Energy • The energy required to remove an electron from an atom is called ionization energy • This is measured in the gaseous state • The energy required to remove the first electron from an atom is called the first ionization energy

11. First ionization energy tends to decrease from top to bottom within a group and increase from left to right across a period

12. The first ionization energy decreases as we move down a group As atomic size increases, the nucleus has a smaller effect on the electrons in the upper energy levels Group Trends in Ionization Energy

13. The first ionization energy of representative elements tends to increase from left to right across a period Nuclear charge increasesfrom left to right but theshielding effect remainsconstant So, the attraction of the nucleus for an electron increases from left to right Periodic Trends in Ionization Energy

14. Ionization Energies for Successive Electrons

15. Trends in Ionic Size • During reactions between metals and nonmetals • metal atoms tend to lose electrons • nonmetal atoms tend to gain electrons • This affects the size of the resulting ions • Cations are always smaller than the atoms from which they form • Anions are always larger than the atoms from which they form

16. Examples of Atomic vs. Ionic Size

17. Trends in Electronegativity • Electronegativity is a property that helps predict the type of bond that will form during a reaction • Electronegativity values decrease from top to bottom within a group • For representative elements, the values tend to increase from left to right across a period

18. Electronegativity Values

19. Summary of Trends