1. Unit 2 – The Periodic Table

2. Development of the Periodic Table
1817 – Dobereiner
Grouped elements in TRIADS…
Three elements with similar properties

3. Development of the Periodic Table
1870 – Mendeleev
Created an 8 Column table based on ATOMIC MASS
Elements with similar properties were in the same column

4. Development of the Periodic Table
Problems :
Some elements did not fit the order.
Tellurium (Te) and Iodine (I)
There were gaps in the table
Able to predict the properties and masses of the unknown elements very accurately.

6. Development of the Periodic Table
1913 – Moseley
Arranged elements with increasing ATOMIC NUMBER
PERIODIC LAW:
Properties of the elements are a periodic function of their atomic number

8. Modern Periodic Table The table is arranged by valence electrons….
Definition: The electrons in the outermost level of the atom.
Bohr Model:
Level 1 = 2 electrons.
Level 2 = 8 electrons.
Level 3 = 18 electrons.
Level 4 = 32 electrons.

9. Modern Periodic Table

10. Modern Periodic Table

12. Modern Periodic Table OCTET RULE…
8 electrons in the outer level = FULL VALENCE SHELL.
Full Valence Shell = Unreactive = Very Stable.
Atoms react with other atoms to make a situation where all atoms end up with FULL VALENCE SHELLS.
They may add electrons.
They may lose electrons.
They may share electrons.

13. 1. Gases or BRITTLE solids.
Metals vs. Nonmetals
METALS
NONMETALS
1. Typically Solids.
1. Gases or BRITTLE solids.
2. Shiny.
2. Dull.
3. Conductor
3. Insulators
LOSE electrons
GAIN electrons

14. Metals vs. Nonmetals REMEMBER… Metals: 3 or less valence electrons.
5 or more valence electrons.
Metalloids:
Properties of both Metals and Nonmetals.
Semiconductors.

15. Metals vs. Nonmetals