Electron Configuration and Orbital Diagrams: A Comprehensive Guide for Chemistry Students, Exercises of Chemistry

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Using Subshell Notation and Orbital Diagrams

 All electrons in an atom are placed into shells according to electron energies.

 These shells are labeled with the integers, starting from one up to infinity, with one being the lowest energy.

 The order for filling subshells is (sometimes called the Aufbau filling order):

1s 2s 2p 3s 3p 4s 3d 4p 5s 4d

5p 6s 4f 5d 6p 7s 5f 6d 7p

Electrons are placed in the lowest energy level first.

 To write an electron configuration using the subshell notation, a combination of the subshell followed by a superscript indicating the number of electrons in that subshell is used.

 Thus, for the first two elements, we would

write their electron configurations as:

H: 1s^1 and He: 1s^2

 For the next element, Li, we can't put a third electron into the 1s subshell because it is full. Thus, we would need to got to the next available subshell - the 2s.

 Li: 1s^2 2s^1

Shows the arrangement of electrons in an

atom by energy level.

 To do a shorthand configuration for any element, count backwards from that element until you reach a noble gas.

 Write that element in brackets. Then, continue forward with next subshell(s)

 One of the reasons for doing this is also to distinguish between core and valence electrons.

 Core electrons are held very tightly by the atom and do not interact when bonds are formed to make compounds. These include the noble gas configuration plus any completely filled d- subshells.

 The valence, or outer shell, electrons are the ones that interact with each other when bonds formed are therefore very important.

 These are always the outermost shell of electrons plus any unfilled d-subshell.

 Note that for any main group element, the number of valence electrons always equals the group number!

 For sodium, it has ten core electrons (neon has ten electrons) and one valence electron (it is in group 1A).

 When writing longhand or shorthand notation each p orbital, d orbital and f orbital gets and individual variable

 So, for 2p or instance the first 2p orbital would be 2px, the second 2py and the last 2pz. A full 2p would look like this: 2px^2 2py^2 2px^2

This is used instead of the boxes and arrows to show the correct distribution of the Aufbau Principle and Hund’s Rule.

 An atomic orbital can hold a maximum of 2 electrons and those 2 electrons must have opposite spins.

 An electron is represented by an arrow.

 Spin is represented by the arrow facing up or down.