ELECTRON CONFIGURATION The electron configuration of an element describes how electrons are distributed in its atomic orbitals. Electron configurations of atoms follow a standard notation in which all electron-containing atomic subshells (with the number of electrons they hold written in superscript) are placed in a sequence. For example, the electron configuration of sodium is 1s 22s22p63s1. Electron Configurations Provide Insight on the Energy Level of the Orbital, the Type of Orbital, and the Total Number of Electrons in the Orbital. However, the standard notation often yields lengthy electron configurations (especially for elements having a relatively large atomic number). In such cases, an abbreviated or condensed notation may be used instead of the standard notation. In the abbreviated notation, the sequence of completely filled subshells that correspond to the electronic configuration of a noble gas is replaced with the symbol of that noble gas in square brackets. Therefore, the abbreviated electron configuration of sodium is [Ne]3s1 (the electron configuration of neon is 1s22s22p6, which can be abbreviated to [He]2s22p6). Aufbau Principle - named after the German word ‘Aufbeen’ which means ‘build up’. - dictates that electrons will occupy the orbitals having lower energies before occupying higher energy orbitals. - The energy of an orbital is calculated by the sum of the principal and the azimuthal quantum numbers. - According to this principle, electrons are filled in the following order: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p… - The order in which electrons are filled in atomic orbitals as per the Aufbau principle is illustrated below. Writing Electron Configurations with the Aufbau Principle - ORBITAL FILLING DIAGRAMS AND ELECTRON CONFIGURATIONS An orbital diagram, or orbital box diagram, is a way of representing the electron configuration of an atom. A box, line, or circle, is drawn to represent each orbital in the electron configuration (using the Aufbau Principle to order the orbitals and hence the boxes, lines or circles, as shown below) 1s → 2s → 2px 2py 2pz → 3s → 3px 3py 3pz → 4s → 3dxy 3dxz 3dyz 3dx2-y2 3dz2 → 4px 4py 4pz → 5s - - Arrows (or half arrows) are used to represent the electrons occupying the orbitals. Arrows (or half arrows) can point up or down: ⚛ electrons with "up spin" are drawn either as upward pointing arrows, ↑, or half arrows, ↿ ⚛ electrons with "down spin" are drawn either as downward pointing arrows, ↓, or half arrows, ⇂ A maximum of 2 arrows can be drawn in each box (because a maximum of 2 electrons can occupy an orbital) When 2 arrows occupy the same box we refer to the electrons as paired, and we must apply the Pauli Exclusion Principle so that these arrows face in opposite directions (one "spin up", one "spin down"). (The paired electrons are said to have antiparallel spin). ↑↓ or ↿⇂ - One arrow is positioned in each box according to Hund's Rule which tells us to maximise the number of unpaired electrons in orbitals of the same subshell, and, to give those electrons the same "spin" (parallel spin). s s p subshell subshell subshell ↑↓ ↑↓ ↑ ↑ 1s 2s 2px 2py 2pz - This sublevel configuration can be broken down into orbitals (boxes). 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6........ SAMPLE: Atomic number of carbon, Z = 6 Electron configuration 1s22s22p2 Use the order of fill diagram to draw an orbital filling diagram with a total of six electrons. Follow Hund’s rule. Write the electron configuration. ELECTRONIC CONFIGURATION/ORBITAL DIAGRAM A. Write the electron configuration [EC] and orbital diagram [OD] of the following elements: 1. Sodium EC = ___________________________________________________________________ OD = 2. Iron EC = ___________________________________________________________________ OD = 3. Bromine EC = ___________________________________________________________________ OD = 4. Barium EC = ___________________________________________________________________ OD = 5. Neptunium EC = ___________________________________________________________________ OD = 6. Erbium EC = ___________________________________________________________________ OD = 7. Lead EC = ___________________________________________________________________ OD = 8. Rubidium EC = ___________________________________________________________________ OD = 9. Titanium EC = ___________________________________________________________________ OD = 10. Calcium EC = ___________________________________________________________________ OD = 11. Gallium EC = ___________________________________________________________________ OD = 12. Tungsten EC = ___________________________________________________________________ OD = 13. Tellurium EC = ___________________________________________________________________ OD = 14. Copper EC = ___________________________________________________________________ OD = 15. Molybdenum EC = ___________________________________________________________________ OD =
