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History of Atom & Periodic Table (Modern periodic Table (100ish…
History of Atom & Periodic Table
Atomic Structure
1
solid tiny spheres that could not be divided
different spheres, different elements
2
experiments of charge and mass
must contain smaller negative charged electrons
plum pudding model
atom as ball of positive charge
electrons struck in it
3
aplha particles at thin sheet of gold
Expected pass straight through or deflect slightly because positive charge very spread out in pudding model
most went straight through, some deflects lots and some deflected backwards
nuclear model,
tiny positive nucleus with mass
cloud of negative electron
most of atom empty space
Bohr's Nucler Model
realised electron would be attracted to nucleas and collapse
All electrons contained in shells fixed distant from nucleus
Further experiments supported this
Later experiments showed
nuclues split into protons
positive charge could be subdivided into whole number of small particles, each with the same charge
John Chadwick work,
neutrons in the nucleus
about 20 years after nuclues model
5
new experimental evidence may lead to change in model
Electonic structure
occupy shells (energy levels)
lowest always filled first
1st sell: 2, 2nd & 3rd: 8
Atoms happier when have full outer shell
most atoms, out shell not full so want to react to fill
History of Periodic Table
no idea of protons
arranged by relative atomic mass, not properties
saw Periodic pattern in properties
gaps, and some in wrong group
as following strict atomic weight
Mendeleev
put 50 known elements in Table, with gaps
in atomic mass, but did change if propeties meant needed change
left gaps to keep similar property together
later gaps filled showing his ideas as correct
isotopes discovery confirmed right not to put in fixed relative atomic mass positions
Modern periodic Table
100ish elements from which all materials are made
laid out in increasing atomic (proton) number
like this there are repeating patterns in element properties
metal found to the left, non-metal to the right
Elements with similar properties form columns
Group number tells you how many electrons in outer shell except Group 0, full outer shell
Rows are called periods. Each new period represents another full shell of electrons, similar properties at regular intervals