![]() ![]() SHAPES OF ORBITALS Five d orbitals make the d sub-shell four are double dumb-bell shaped the other a dumb-bell with a collar SHAPES OF ORBITALS Three p orbitals make the p sub-shell dumb-bell shaped SHAPES OF ORBITALS One s orbital makes the s sub-shell spherical DO NOT USE THE WORD ORBIT WHEN YOU MEAN AN ORBITAL (Pauli Exclusion Principle) Orbitals have different shapes depending on which sub-shell they are in. (Heisenberg’s Uncertainty Principle) Orbitals can hold one electron or two electrons as long as they have opposite spin. HEISENBERG’S UNCERTAINTY PRINCIPLE “You cannot determine both the position and momentum of an electron at the same time.” PAULI’S EXCLUSION PRINCIPLE “No two electrons can have the same four quantum numbers.” THE AFBAU (BUILDING UP) PRINCIPLE “Electrons enter the lowest available energy level.” HUND’S RULE OF MAXIMUM MULTIPLICITY “When in orbitals of equal energy, electrons will try to remain unpaired.”ĮLECTRONS OCCUPY ORBITALS An orbital is a region in space where there is a 95% probability of finding the electron. RULES AND PRINCIPLES ARISING FROM QUANTUM MECHANICS These four rules govern how electrons are arranged in atoms. Shell 1 contains only an s sub-shell Shell 2 contains an s and p sub-shell Shell 3 contains an s, p and d sub-shell Shell 4 contains an s, p, d and f sub-shell d p s d p s p s How are electrons arranged within these sub-shells? s ![]() The electrons in different sub-shells have different energy levels. Maximum electrons per shell 1st shell 2 2nd shell 8 3rd shell 18 4th shell 32 The theory couldn’t explain certain detailed aspects of the chemistry of the elements or their emission spectra.Ĥ 3 INCREASING ENERGY / DISTANCE FROM NUCLEUS 2 1 SHELLS, SUB-SHELLS AND ENERGY LEVELS SUB SHELLS PRINCIPAL QUANTUM NUMBER OF SHELL f A study of First Ionisation Energies across each period suggested that each ‘shell’was in fact a group of ‘sub-shells’ at different but similar energy levels. THE BOHR MODEL OF THE ATOM A small nucleus of protons and neutrons surrounded by electrons in shells each shell holding up to a maximum number of electrons and filled from the first shell outwards electrons in the first shell being the most strongly held and therefore at the lowest energy level. ![]()
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