Chapter 1 - Elements and the Periodic Table
Robert Boyle defined an element as a substance that cannot be broken down into simpler substances.
Humphry Davy developed electrolysis to break down compounds into elements
Dobereiner:
- He proposed the Law of Triads.
- He grouped elements of similar properties in groups of three, called triads.
Newlands
- He proposed the Law of Octaves.
- He arranged the elements in order of increasing atomic weight.
- He found that properties seemed to repeat themselves every 8th element.
Mendeleev created the first periodic table.
| Mendeleev’s Table | Moseley’s (Modern) Table |
|---|---|
| Elements arranged in order of increasing atomic weight. | Elements arranged in order of increasing atomic number. |
| Gaps left for undiscovered elements | Gaps have been filled |
| Group 8 elements missing | Group 8 elements included |
Henry Moseley discovered in 1913, using X-rays, that each element had a different atomic number.
Group 1 - Alkali Metal Physical Properties:
Soft metals – they can be cut with a knife
Low densities – They float on water. Li, Na & K have a density less than 1 g/cm3
\n Group 1 - Alkali Metal Chemical Properties:
Reactivity increases down the group.
Metallic shine when freshly cut but quickly tarnishes (shine disappears quickly due to reaction of surface with oxygen in the air to form a metal oxide)
Burn readily forming the metal oxide.
React vigorously with water forming an alkaline solution and H2 gas.
Stored in oil to prevent reactions with water and oxygen in the air.
\n Group II - The Alkaline Earth Metals: \n Physical Properties: Harder than corresponding alkali metals.
Chemical Properties: Reactivity increases down the group and they are less reactive than corresponding alkali metals.
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