Electron Structure

• An early model of the atom was the Bohr model (GCSE model 2 electrons in first shell, 8 in second etc.) with electrons in spherical orbits.
• Early models of atomic Structure predicted that atoms and ions with noble gas electron arrangements should be stable.
• Electrons are arranged on

  • principle energy levels numbered 1,2,3,4. 1 is closer to the nucleus
  • These are then split into sub every levels labelled s,p,d,f. S holds up to 2 electrons, p holds up to 6 electrons, d holds up to 10 electrons, f hold up to 14 electrons
  • These sub levels are then split into orbitals which hild up to 2 electrons on opposite spin
• Orbitals represent the mathematical probabilities of finding an electron at any point within certain spatial distributions around the nucleus. Each orbital has its own approximate , three dimensional shape. It is nit possibke to draw the shaoe of orbitals precisely
• On principle level 1 the sub level is 1s
• On principle level 2 the sub levels are 2s and 2p
• On principle level 3 the sub levels are 3s, 3p and 3d
• On principle level 4 the sub levels are 4s, 4p, 4d and 4f
• An atom fills up the shells in order of increasing energy (3d is higher in energy than 4s and so gets filled after the 4s)

  1s->2s->2p->3s->3p->->4s->3d->4p->5s->4d->5p
• The electronic structure of oxygen is

  1s²,2s²,2p⁴

  • The big numbers represents the number of the main energy level
  • The letters are the type of sub energy level
  • The little numbers represent the number if electrons in the sub level
• The electron configuration for calcium is

  1s²,2s²,2p⁶,3s²,3p⁶,4s²
• Using spin diagrams

  • An arrow represent one electron
  • Box represents one orbital
  • The arrows going in the opposite direction represents the different spins of the electrons in the orbital
• When filling up sublevels with several orbitals, fill each orbital singly before starting to pair up the electrons
• The periodic table is split into blocks

  • A s block element is one whose outer electron is filling a s-sub level shell e.g sodium 1s²,2s²,2p⁶,3s¹
  • A p block element is one whose outer electron Is filling a p-sub level shell e.g chlorine 1s²,2s²,2p⁶,3s²,3p⁵
  • A d block element is one whose outer electron is filling a d-sub level shell e.g vanadium 1s²,2s²,2p⁶,3s²,3p⁶,4s²,3d³
• What is the electron structure for positive ions

  When a positive ion is formed electrons are lost from the outermost shell

  E.g Mg is 1s²,2s²,2p⁶,3s² becomes Mg²+ which is 1s²,2s²,2p⁶
• What is the electron structure for negative ions

  When a negative ion is formed electrons are gained

  Oxygen is 1s²,2s²,2p⁴ becomes O²- which is 1s²,2s²,2p⁶
• The electronic structure of the d-block has some complications.

  • 4s fills before 3d and so we write them in that order.
  • Chromium and copper have an unusual arrangement in having a half filled 4s sub shell
  • When d block elements form ions they lose the 4s electrons first