1. Periodicity
Trends in physical and chemical properties demonstrated by the periodic table of the elements

2. The Periodic Table
Each horizontal row (“period”) represents a new energy level

3. The Periodic Table
Elements in the same period have valence electrons in the same energy level

4. The Periodic Table
So the energy level increases as you move down the periodic table one period at a time

5. The Periodic Table
Each new energy level is further from the nucleus than the energy level below it

6. The Periodic Table
Distance from the nucleus matters because at greater distances, the forces between charged particles decreases

7. The Periodic Table
As you move across a period left to right, the energy level is the same but the atomic number increases (remember atomic # = # of protons)

8. The Periodic Table
More protons will exert more force of attraction than fewer protons (assuming the same distance between them)

9. Periodic Trends
There are a number of physical and chemical properties that we will examine that form trends as you move down and across the periodic table
Atomic Size (Radius)
The radius of an atom is the distance from the center of the nucleus out to the valence energy level
Ionization Energy
Ionization energy is the energy it takes to remove a single electron from a neutral atom
Electronegativity
Electronegativity is the relative force that an atom will exert on electrons from another atom when they bond together

10. Atomic Radius

11. Atomic Radius
As you move down the table from top to bottom, valence electrons are at progressively higher energy levels
Atomic Radius increases from top to bottom

12. Atomic Radius
As you move across the table left to right the energy level is the same, but there is an increase in the number of protons
More protons means more attraction to the electrons, pulling them closer
Atomic Radius decreases from left to right in the same period

13. Ionization Energy

14. Ionization Energy
As you move across the period, elements have the same valence energy level, but progressively MORE PROTONS

15. Ionization Energy More protons results in stronger attractions
Stronger attractions result in more energy needed to take an electron

16. Ionization Energy
Note that ionization energy increases across the period, but has a few dips at the points where new orbital types start to fill

17. Ionization Energy
Note also that ionization energy is very high for the noble gases, and very low for the group 1 metals

18. Ionization Energy
The noble gases not only have the largest number of protons in their period, they also have a stable electron configuration

19. Ionization Energy
The group 1 metals are the elements that start a new period.
A new period is a new energy level
Further from the nucleus means less force of attraction, so easier to remove an electron

20. Electronegativity

21. Electronegativity
The relative amount of force of attraction that an atom will have to electrons from another atom

22. Electronegativity
High electronegativity indicates a strong hold on electrons the atom is sharing in a chemical bond
Low electronegativity = weak hold on the electron pair

23. Electronegativity Difference
If the two atoms have equal electronegativity, they will pull equally on the electron pair
Electrons will be shared equally
This is a nonpolar covalent bond
If the two atoms have significantly different electronegativities they will not pull equally on the electron pair, so the sharing will not be equal
This is either polar covalent or ionic bonding