Electron Configurations

Where are the electrons? Do they exist in orbits like our planets? NO! The Bohr model is a useful representation but it doesn’t tell the whole story.

Where are the electrons? Do they exist in electron clouds? In a sense. However, we can explain even more completely the nature of electrons.

Electron Configurations Electrons exist in regions of probability called orbitals. There are four different types of orbitals – s, p, d, and f.

Electron Configurations Every energy level has one s-orbital. The s-orbitals in the different energy levels are labeled 1s, 2s, 3s, 4s, etc.

Electron Configurations p-orbitals come in sets of three. Every energy level, except the first, has three p-orbitals. The p-orbitals in the different energy levels are labeled 2p, 3p, 4p, etc.

Electron Configurations d-orbitals come in sets of five. Every energy level, starting with the third, has five d- orbitals. The d-orbitals in the different energy levels are labeled 3d, 4d, 5d, etc.

Electron Configurations f-orbitals come in sets of seven and don’t exist until the fourth energy level. The f-orbitals in the different energy levels are labeled 4f and 5f.

Electron Orbitals Every electron orbital can hold up to 2 e -. An s-orbital can hold 2 e -. A set of 3 p-orbitals can hold 6 e - (2 each). A set of 5 d-orbitals can hold 10 e - (2 each). A set of 7 f-orbitals can hold 14 e - (2 each). Do you notice a correlation with the periodic table?

Summary What kind of orbitals exist in the first energy level? How many total orbitals are there in that level? How many total electrons can be in that level?

Summary What kind of orbitals exist in the second energy level? How many total orbitals are there in that level? How many total electrons can be in that level?

Summary What kind of orbitals exist in the third energy level? How many total orbitals are there in that level? How many total electrons can be in that level?

Summary What kind of orbitals exist in the fourth energy level? How many total orbitals are there in that level? How many total electrons can be in that level?

Electron Configurations With just a couple pieces of information, we can predict which orbitals the electrons of an atom are likely to hang out in. Aufbau (building-up) principle – electrons will fill lowest energy orbitals first. Of course, to use the Aufbau principle, we need to know the relative energies of our orbitals.

Electron Configurations Look at the periodic table. Trace your finger from element 1 to element 25 without skipping any elements. What orbitals did you come across as you traced? 1s2s2p3s3p4s3d This is the order that the orbitals will fill. For bigger elements, you can continue to trace.

Electron Configurations Example: What is the electron configuration for hydrogen? H:1s 1 The one electron is in the lowest energy orbital.

Electron Configurations Example: What is the electron configuration for helium? He:1s 2 Both electrons can exist in the 1s orbital. The superscript is not an exponent. It tells how many electrons are in that orbital.

Electron Configurations Examples: What is the electron configuration for lithium? for carbon? for magnesium? for chlorine? for zinc? for silver (Z = 47)? for promethium (Z = 61)?

Electron Configurations SHORTCUT! We can write electron configurations in kernel notation (or noble gas notation). The most important electrons are the valence electrons. (valence electrons are the electrons in the highest energy level) We can replace the configuration of a noble gas with its symbol.

Electron Configurations Write the configuration for calcium using noble gas notation. Ca: 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 Ca: [Ar]4s 2

Electron Configurations Examples: Write the electron configuration for these using kernel notation. magnesium chlorine zinc silver promethium