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

6. Another View

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

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 Na + Cl -

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. Group Trends in Ionization Energy
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

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

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