1. Development of the Periodic Table
Mendeleev developed periodic table to group elements in terms of chemical properties.
Alkali metals develop +1 charge, alkaline earth metals + 2
Nonmetals usually develop negative charge (1 for halides, 2 for group 6A, etc.)
Blank spots where elements should be were observed.
Discovery of elements with correct properties.
John A. Schreifels
Chemistry 211

2. Periodic Properties
Periodic law = elements arranged by atomic number gives physical and chemical properties varying periodically.
We will study the following periodic trends:
Atomic radii
Ionization energy
Electron affinity
John A. Schreifels
Chemistry 211

3. Periodic Trends
OBJECTIVES:
Interpret group trends in atomic radii, ionic radii, ionization energies, m.p., b.p., electronegativity and chemical properties

4. Trends in Atomic Size
First problem: Where do you start measuring from?
The electron cloud doesn’t have a definite edge.
They get around this by measuring more than 1 atom at a time.

5. Atomic Size }
Radius
Atomic Radius = half the distance between two nuclei of a diatomic molecule.

6. Trends in Atomic Size Influenced by three factors: 1. Energy Level
Higher energy level is further away.
2. Charge on nucleus
More charge pulls electrons in closer.
3. Shielding effect
e <-> e repulsion

7. Shielding
The electron in the outermost energy level experiences more inter-electron repulsion (shielding).
Second electron has same shielding, if it is in the same period

8. Periodic Trend Metals are at the left of the table.
They let their electrons go easily
At the right end are the nonmetals.
They want more electrons.
Try to take them away from others

9. Periodicity and chemical properties
Most obvious trend is from metallic to non-metallic
Acid-base properties of oxides:
Metal oxides tend to be basic
(Na2O = NaOH in H2O)
Nonmetal oxides tend to be acidic
(SO2 = H2SO3 in H2O)

10. Periodic Table/Periodicity
Who? Newlands, Mendeleev, Moseley
Layout
Main, Transition, Lanthanides, Actinides
Metals, Non-metals, Metalloids
Properties
Groups (Families), Periods
Periodic Law
Trends – Atomic Radii, Valence Electrons

11. Periodic Table: Arrangement
Layout of the Periodic Table: Metals vs. nonmetals
Nonmetals
Metals

12. Across the Periodic Table
Periods: Are arranged horizontally across the periodic table (rows 1-7)
These elements are in the same energy level
2nd Period
6th Period

13. Down the Periodic Table
Family: Are arranged vertically down the periodic table (group or 1-8 A,B)
These elements have the same number electrons in the outer most shells, the valence shell.
Alkali Family:
1 e- in the valence shell
Halogen Family:
7 e- in the valence shell

15. Group trends As we go down a group...H
As we go down a group...
each atom has another energy level,
so the atoms get bigger. Li Na K Rb

16. Periodic Trends As you go across a period, the radius gets smaller.
Electrons are in same energy level.
More nuclear charge.
Outermost electrons are closer. Na Mg Al Si P S Cl Ar

17. Rb K
Overall Na Li
Atomic Radius (nm) Kr Ar Ne H 10
Atomic Number

18. Summary Periodic Table: Map of the Building block of matter
Type: Metal, metalloid and Nonmetal
Groupings: Representative or main, transition and Lanthanide/Actanides
Family: Elements in the same column have similar chemical property because of similar valence electrons
Alkali, Alkaline, chalcogens, halogens, noble gases
Period: Elements in the same row have valence electrons in the same shell.