Lesson 24

Shell Game

Electron Configuration

electron configuration - a shorthand notation to keep track of the electrons in an atom

• Atoms of elements are arranged on the periodic table by shell numbers. Period one elements have one she'll and period two elements have two shells and so on. Up until period 4 and up all have only four shells.
• Now each shell of an atom has a certain number of subshells. Shell one is only one shell total. Shell two has two subshells for two total, shell three has three total subshells, and shell four has four total subshells.
• Shells are ordered by the 1st subshells are the s shells, 2nd subshells are the p subshells,3rd subshells are the d subshells, and 4th subshells are the f subshells.

            - s subshells are only able to hold a maximum of 2 electrons. Groups 1 & 2

            - p subshells can hold a maximum of 6 electrons. Groups 3-8

            - d subshells can hold a maximum of 10 electrons. Transition metals

            - f subshells can hold a maximum of 14 electrons. Two rows at the bottom

Ex: magnesium, Mg, is in period three so it has three shells, so its electron configuration is 1s2 because the first s subshell is full and can only have a maximum of two electrons, then 2s2 2p6 because all the second subshells are full and p subshells have a maximum of 6 electrons, then 3s2 and it ends there because magnesium is the second element in period 3.

Ex: phosphorous, P, 1s2 2s2 2p6 3s2 3p3

When writing electron configuration, the order of filling in subshells doesn't always go in numerical order. In the middle of the periodic table are the transition metals, the first row of which is in period 4. However The first row is 3d and in period 5 the row of transition metals is 4d. So, when naming elements after the transition elements the numerical order is messed up.

Ex: Germanium, Ge, 1s2 2s2 2p6 3s2 3p6 4s2 3d10 (3d comes after 4s because it is the first row of transition metals and transition metals can hold a maximum of 10 electrons) 4p2.

An even easier way to write the electron configuration is in Noble Gas Shorthand. This means you take the last noble gas before the element you are writing it for and then the regular configuration after that.

Ex: if you want to write the noble gas shorthand for Strontium, Sr, first find the noble gas that came before it which is Krypton, Kr. Put the noble gas in brackets like this - [Kr]. Then use regular configuration afterwards like this - [Kr] 5s2.

Practice problems
4) n-1 has 1 subshell, n-2 has 2 subshells, n-3 has 3 subshells, n-4 has 4 subshells.

5) 14 total subshells

7) 4p

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