ELECTRONS IN ATOMS
By Alex Pac, Page 6
Steps for determining electron configurations:
- Identify how many electrons are in the atom.
Example: Carbon has 6 electrons
- Determine the principal energy level (n) of the atom
n = 2 for carbon (it is in the second period)
- Determine the number of sublevels.
· In principal energy level 1, there is 1 (1s).
· In principal energy level 2, there are 4 (2s, 2p, 2p, 2p)
· So for carbon we are working with 5 potential sublevels (they might not all be used).
- Assign electrons to the sublevels following the three rules (Aufbau, Pauli Exclusion, and Hund’s).
· 1s will be filled first, with the maximum of 2 electrons. You still have four electrons left.
· 2s will be filled next, with the maximum of 2 electrons. You still have two electrons left.
· 2p will be filled next, with the maximum of 2 electrons. You don’t have any electrons left now.
- Write the complete electron configuration.
Notice that the superscripts (the electrons in each sublevel) add up to the total number of electrons in the atom. 2 + 2 + 2 = 6
- To write the abbreviated electron configuration, determine what the previous noble gas is from looking at the periodic table.
The noble gas which comes before carbon is helium.
- Identify the portion of carbon’s electron configuration that is the same as helium’s electron configuration.
Helium, which has 2 electrons, has an electron configuration of 1s2.
- Substitute the chemical symbol of the noble gas surrounded by brackets into the original electron configuration to make the abbreviated electron configuration.
Follow 3 rules: Aufbau, Hunds , Pauli
- Arrows represent electron (up/down)
- Orbitals are line bellow arrows
- Primary energy level and sub level under orbital (like a fraction)
- Fill in lowest energy to highest energy first (Aufbau principa, diagonal rule)
- Individually fill in orbitals of sub level first before doubling up (Hunds rule)
- If two electors in the same orbital have one arrow point up and the other point down to show difference in spin. ( Pauli's exclusion principal)