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Element a substance which cannot be broken down further by chemical means
History of Ideas of Elements
- Ancient Greeks idea of basic substances from which all other materials are made (earth, air, fire and water)
- Robert Boyle idea that elements cannot be broken down into simpler substances
- Humphrey Davy developed electrochemical techniques to break down substances
- Henry Moseley idea of atomic numbers
Periodic Table
Groups vertical columns Periods horizontal rows
S-Block Elements Groups I and II
- Reactive metals
- Low boiling and melting points
- Low densities
P-Block Elements Groups III, IV, V, VI, VII, VIII
- Mostly non-metals
D-Block Elements Group II and III
- Divided into sub groups e.g. copper, gold and silver make up the copper subgroup
Law of Triads
- Suggested by Dobereiner
- Grouped elements with similar properties into groups of three
- Only a small number of triads were found to exist
Law of Octaves
- Suggested by Newlands
- Found that properties seemed to repeat themselves every 8 elements
- Only workes for the first 17 elements
Periodic Table
- Compiled by Mendeleev
- Elements arranged in order of atomic mass, except for iodine and tellurium (this was accounted for with the discovery of atomic numbers)
Differences between Mendeleev’s table and the modern periodic table
Mendeleev’s periodic table Modern periodic table
- Gaps left for undiscovered elements Gaps filled
- No group VIII elements Group VIII elements included
- Elements discovered since 1869 missing Elements discovered since 1869 included
- D-Block elements beside main groups D-block elements in seperate block
- Arranged in increasing atomic weight Arranged in increasing atomic number
Alkali Metals
Very reactive, increasing in reactivity down the group
Physical Properties
- Soft metals
- Low densities
Chemical Properties
- Tarnished by air – metal oxide formed (4Na + O2 >>> 2Na2O)
- Must be stored in oil
- Reacts vigourously with water (2Na + 2H2o >>> 2NaOH + H2)
Alkaline Earth Metals
Less reactive than the alkali metals, increasing in reactivity down the group
Physical Properties
- Harder metals than alkali metals
Chemical Properties
- React with water to form hydroxide (2Ca + H2O >>> Ca(OH)2 + H2)
Halogens
Very reactive non-metals, decreasing in reactivity down the group
Physical Properties
- Low melting and boiling points
Chemical Properties
- React with hydrogen to form acidic solutions hen dissolved in water
- React with alkali metals to form white salts (2Na + Cl2 >>> 2NaCl)
Noble Gases
Least reactive of all the metals
Physical Properties
- Boiling point increases down the group
Types of Gases
Monoatomic Gases Ne
Diatomic Gases H2, O2
Triatomic Gases O3
