Levels of Organization• The term, ‘electron cloud’ doesn’t tell usvery much about electron location.• This cloud is actually highly structured.• It is divided into:– Principal energy levels (PELs or shells )• Energy sublevels (or subshells)–Orbitals
PEL Review• Atoms may have from 1-7 PELs that areconcentric spheres.• Level 1 is closest to the nucleus andlevel 7 found only with the largestatoms is the highest PEL.
Energy Sublevels• Principal energy levels are subdividedinto 1-4 sublevels, depending on howlarge the PEL is.• Sublevels are designated as s, p, d andf.• Each sublevel has a different number oforbitals, and the orbitals have differentshapes.
Orbitals• An orbital is the region of space wherethere is a 90% probability of finding anelectron of a particular energy.• A single orbital may be home to 1 or 2electrons, but never more than 2.
The ‘s’ sublevel• The ‘s’ sublevel is the simplest.• It has only 1 orbital, which is a sphere.• The orbital can house 2 electrons.
Reality• Please keep in mind that orbitals arenot solid shapes as the previous picturesuggests. The sphere represents 90%electron density.• A real orbital would probably have afuzzy appearance, more like this.
The ‘p’ sublevel• The ‘p’ sublevel is largerthan the ‘s’ and consistsof 3 orbitals which eachlook like this.• The p-orbital is bi-lobedand can also house 2electrons.• The grey circle in thecenter represents the s-orbital.
The ‘p’ sublevelz• The ‘p’ sublevelconsists of 3orbitals, each atright angles to eachother in space.• Thus, the entiresublevel can hold upto 6 electrons total.yx
The ‘p’ sublevelz• The 3 orbitals of thep-sublevel aredesignated as p x , p yand p z for the 3axes upon whichthey lie in space.yx
The ‘d’ sublevel• The ‘d’ sublevel consists of 5 orbitalswhose shapes are more complex.• The sublevel can house 10 electrons.• The orbitals have 2 different types ofshapes, and are oriented in space so asnot to overlap each other.
d- orbitals• Four of the d-orbitals look likethis.The fifth d-orbitallooks like this.
‘d’ sublevel• Altogether, the d-orbitals occupy acommon space, butdo not overlap eachother.• The whole sublevellooks like this.
‘f’ sublevel• The ‘f’ sublevel has 7 orbitals, home to 14electrons and is much more complex.• The orbitals look like this.
Heisenberg Uncertainty Principle• The whole idea that electrons occupy 3-dimensional volumes of space camefrom Werner Heisenberg who said thatwas impossible to know both the speedand location of tiny, fast-movingelectrons at the same time.• This became know as the “HeisenbergUncertainty Principle.”
Pauli Exclusion Principle• Another famousphysicist, WolfgangPauli stated that asingle atomic orbital,regardless of size orshape can only hold2 electrons, andthose electrons musthave opposite spin.
Electron Spin• Like charge, particleshave another qualitycalled ‘spin.’• There are only 2possible values,parallel (up) or antiparallel(down).
Putting It All Together• PEL 1 is small and ‘close’ to the nucleus.• It only has 1 sublevel, an ‘s’ and so hasroom for only 2 electrons.• When the 1 st PEL is filled with 2 e - , thenext electrons must go into the 2 nd PEL.
Putting It All Together• The 2 nd PEL is larger, and so has roomfor more electrons.• It has an ‘s’ sublevel, and a ‘p’ sublevel.• The ‘s’ has room for 2 e - while the ‘p’sublevel with its 3 orbitals, has room for6 more, giving a total of 8 electrons inthe 2 nd PEL.
Putting It All Together• PEL 3 is larger still, and has room for agreater number of electrons.• It has s, p and d sublevels.• The ‘s’ sublevel can hold 2 e - , the ‘p’can hold 6, and the ‘d’ can hold 10 (5orbitals) for a total of 18.
Putting It All Together• PELs 4-7 all have s, p, d, and f possiblesublevels.• s 2 e - (1 orbital)• p 6 e - (3 orbitals)• d 10 e - (5 orbitals)• f 14 e - (7 orbitals)• Total of 32 electrons.
A Helpful TablePEL1 2 3 4 5-7Sublevelss s / p s p d s p d f Same as4OrbitalsInSublevele- insublevelTotal e- inPEL1 1 / 3 1/3/5 1/3/5/7 Same as42 2 / 6 2/6/10 2/6/10/14 Same as42 8 18 32 Same as4