Topic 1- Atomic Structre And Periodic Table Flashcards
Atoms
Smallest part of an element
Number of electrons = number of protons
No overall charge
Protons = atomic number
Radius = 0.1nm
Elements
Shown on periodic table
Only one type of atom
Reactions
Involve formation of one or more new substances
Detectable energy change
Compounds
2 or more elements chemically bonded in fixed proportions
Only separated by chemical reactions
Mixture
2 or more elements not bonded
Chemical properties unchanged
Can be separated by filtration, crystallisation, distillation and chromatography
1st model of an atom
Tiny invisible spheres
Plum pudding model
Electrons embedded in a positive ball of charge
Nuclear model
Alpha particles shot through gold foil and scattered = mass concentrated in the middle which was charged
Positive nucleus
Later experiments = nucleus could be divided in protons
Niels Bohr
Suggested electrons orbited at specific distances
James Chadwick
Evidence of neutrons
Isotopes
Atoms with different number of neutrons
Still no charge
Different mass number
Electrons
Occupy lowest possible levels (shells)
No mass
Negative charge
Periodic table
Ordered by atomic number
Elements with similar properties and electrons in outer shell = same columns
Early periodic table
Ordered by atomic weight
Incomplete so wrong
Isotopes explained why the atomic mass wasn’t always correct
Mendeleev
Left gaps in his periodic table
Elements predicted by Mendeleev were descobered
