The Periodic Table - History And Use Flashcards
Contribution of the greeks?
Proposed there were four elements; earth, fire, wind and water.
Contribution of Robert Boyle.
Irishman who defined the term element.
Define element.
An element is a substance that cannot be split into simpler substances by chemical means. All the atoms in an element have the same atomic number.
Contribution of Humphry Davy
Discovered potassium, sodium, calcium, and many other elements by passing electricity through their compounds. (Electrolysis)
Contribution of Dobereiner. Give an example.
- Triads
- Have similar chemical properties
- The atomic weight of the middle element is approximately equal to the average of the other two.
Triads: Cl, Br, I ; Li, Na, K
Drawback of Dobereiner’s system.
Few triads could be found; deemed a coincidence.
Contribution of John Newlands.
If the known elements are arranged in order of their atomic weights, the properties repeat every eight elements.
Drawbacks with Newland’s Octaves.
Didn’t take undiscovered elements into account-should have left gaps.
The properties repeat every ninth element in the modern periodic table.
The rules fell apart by the third octave.
Contribution of Mendeleev.
Periodic law-elements arranged in order of increasing atomic weight and elements with similar properties placed beneath each other in groups. Left gaps for undiscovered elements and predicted their properties.
What elements did Mendeleev reverse and why?
Tellurium was placed before Iodine even though it has a larger atomic weight to ensure it was in the same group as elements with similar properties
Contribution of Moseley.
Used x-rays to discover the positive charge of the nucleus. The atomic number. He found that elements in the periodic table are in order of atomic number.
Differences between Mendeleev’s periodic table and the modern periodic table? (5)
Mendeleev:
- Elements arranged in order of increasing atomic weight as opposed to atomic number.
- Contains gaps for undiscovered elements, modern does not.
- Only 60 elements; over 100 in modern table.
- Transition elements not in separate block but are in modern table.
- No inert gases/noble gases but there are in the modern table.
Contribution and mistakes of Lavoisier.
Compiled a list of 33 elements.
E.g. N, C, Cu, Fe
But mistakenly put heat and light in the list.
List the diatomic elements.
Hydrogen Nitrogen Fluorine Oxygen Iodine Chlorine Bromine
Describe the reaction of lithium and water in both words and chemical formulae.
Lithium + water = lithium hydroxide + Hydrogen
2Li(s) + 2H2O(l) = 2LiOH(aq) + H2(g)
