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Atomic Structure and Periodic Table (Atomic Structure (An atom is the…
Atomic Structure and Periodic Table
Atomic Structure
An atom is the smallest part of an element that can exist
Compounds contain 2 or more elements chemically combined in fixed proportions
A mixture is 2 or more elements or compounds not chemically combined
Plum Pudding model suggested atom is a ball of positive charge with negative electrons embedded in it
Alpha particles experiment showed that the mass of an atom is concentrated at the centre, and the nucleus has a positive charge
Neils Bohr suggested energy levels
James Chadwick discovered the neutron
Radius of an atom - 0.1 nm
Isotopes are atoms of the same element with different numbers of neutrons
Periodic table
Elements are arranged in order of atomic (proton) number and so that elements with similar properties are in the same group
Initially were arranged in order of atomic weight
Mendeleev left gaps for some elements that he thought had not been discovered and in some places changed atomic weight order
Group 0 elements are unreactive as they have a stable electronic structure
Alkali metals + water --> metal hydroxides + hydrogen
Halogens react with metals to form a metal salt (ionic compound)
A more reactive halogen can displace a less reactive halogen from an aqueous solution of its salt
Transition metals
Have typical properties of metals
Form coloured compounds
Can be used as a catalyst