1. Periodic Table: Patterns

2. A Few People Dobereiner- organized elements into “triads”
Triad – set of 3 elements with similar properties

3. Newlands Noticed patterns of eight or octaves
Arranged elements based on weight

4. Lothar Meyer
Organized elements in a useful way but does not get as much credit as

5. Mendeleev
Organized elements based on atomic weight - no idea of atomic number or number of protons at this time ~1868

6. Mendeleev’s Table
Left “blank spaces” for elements that had not yet been discovered
He predicted the chemical and physical properties of elements that had yet to be discovered (quite accurately)

7. Mosely
arranged the periodic table by the number of protons (atomic number)
We use this version today

8. Periodic Law
Elements are arranged by increasing atomic number ; there is a periodic repetition in their physical and chemical properties.
Mendeleev and Mosely understood this Periodic Law

9. Periodic Law
It did not work for 100 % of the elements

10. Periodic Table Horizontal rows: Vertical columns: Called Periods
Show the number of the shell or Energy level
Vertical columns:
Called groups or Families
Show the valence electrons
Elements in a group have similar physical and chemical properties

11. Group A Vs. Group B Group A known as the Representative Elements
Includes 1A- 8A
Group B known as the Transition Elements
Includes elements3B, 4B, 5B, 6B, 7B, 8B, 1B , 2B

12. Valence Electrons
Do you remember how to determine the number of valence electrons?
Transition and Inner Transition metals generally have 2 or 1 valence electrons

13. Classification of Elements
Another way to classify (Metals, Nonmetals and Metalloids)

14. Metals, Nonmetals, and Metalloids
There is a zig-zag or staircase line that divides the table.
Metals are on the left of the line, in blue.
Nonmetals are on the right of the line, in orange.

15. Metals, Nonmetals,and Metalloids
Elements that border the stair case, shown in purple are the metalloids or semi-metals.

16. Metals Metals lustrous malleable ductile
good conductors of heat and electricity
Form + ions
They are mostly solids at room temp.
What is one exception?

17. Nonmetals
Nonmetals
Dull
Brittle
Nonconductors (insulators)
Some are solid, but many are gases, and Bromine is a liquid.
Form - ions

18. Metalloids Metalloids (semi-metals)
characteristics of both metals and nonmetals
shiny but brittle
semiconductors

19. Periodic Trends
There are several important atomic characteristics that show predictable trends that you should know.
The first and most important is atomic radius.
Radius is the distance from the center of the nucleus to the “edge” of the electron cloud.

20. Atomic Radius
Distance from the Nucleus of one atom to the nucleus of the other atom
Two Br atoms bonded together are 2.86 angstroms apart. So, the radius of each atom is 1.43 Å.
2.86 Å
1.43 Å

21. Element Characteristics
Atomic radius
Radius size increases
Radius size decreases

22. Atomic Radius Vertical Column – size increases
With each step down the family, we add an entirely new energy level to the electron cloud, making the atoms larger with each step.
Horizontal Row- size decreases (generally)
Each step adds a proton and an electron (and 1 or 2 neutrons).
Electrons are added to existing sublevels. (They are not getting bigger)

23. Effective Nuclear Charge
The effect is that the more positive nucleus has a greater pull on the electron cloud.
The nucleus is more positive and the electron cloud is more negative.
The increased attraction pulls the cloud in, making atoms smaller as we move from left to right across a period.

24. Ionization energy generally decreases
Energy required to overcome the attraction of the nuclear charge and remove an electron from an atom to form an ion
Easier to remove an electron from group 1 than group 8
Easier to remove electrons that are farther away from the nucleus (elements at the bottom of a group)
Ionization energy generally decreases
Ionization energy increases

25. Electronegativity decreases
It is the ability for atoms of an element to attract electrons when they are chemically combined with another element
Electronegativity decreases
Electronegativity increases

26. Element Characteristics
More nonmetallic
Liquids
Periodic Table
More metallic
Solids

27. Periodic Table Trends: Summary
Atomic radius decreases
Ionization energy and
Electronegativity increase