1. 5.1 – NOTES History of the Periodic Table

2. I. Development of the Modern Periodic Table
A. History of the Periodic Table’s Development –
’s, Lavoisier compiled a list of 23 known elements
- Au, Ag known since prehistoric times
- discovery of electricity allowed for the electrolysis of several compounds, led to “new” elements; as did industrial revolution
- by 1870 over 70 elements were known;

4. 1. Dobereiner – 1829
- found triads of elements - trios of elements with similar properties.
Li, Na, K Ca, Sr, Ba Cl, Br, I were some of his triads

5. 2. John Newlands – 1865
- Arranged elements by atomic weight and found that similar elements appeared to be 7 elements apart;
- “Law of Octaves”. He went no further in his classification of the elements.
- When a pattern repeats in a specific manner, said to be periodic;
- wasn’t consistent (didn’t apply to all elements); system failed;
- **In the 1860’s a new system for calculating mass was discovered

6. 3. Meyer, 1869
- Organized the elements, but made no attempt at predictions.
- Demonstrated connection b/t mass and properties like Mendeleev
- also published shortly after Mendeleev;

8. 4. Mendeleev, 1869 – is given credit for organizing the periodic table
- He arranged elements in order of increasing atomic mass.
- Similar elements were placed next to each other in horizontal rows.
- Furthermore, he predicted the existence of 3 missing elements, Sc, Ga, and Ge, and predicted their properties very accurately.
- The family of elements that was completely missing was the noble gases, which had not yet been discovered.
Colorless/odorless/tasteless  no evidence of their presence

9. 5. Moseley –
- Determined the atomic numbers of the known elements and rearranged the periodic table.
- As new elements were discovered, variation in properties was noticed, no longer matched up;
- identification of atomic # fixed the problem and the periodic table was rearranged according to increasing atomic number

10. B. The modern periodic table
- Periodic Law – elements are arranged by increasing atomic #;
vertical columns = families/groups
- similar properties/rxns due to similar e- configurations
- Groups 1A – 8A known as the representative elements b/c possess a wide range of chemical/physical properties;
- horizontal rows = series/periods; demonstrate a slow pattern of change called trends