Electron Configurations: A Comprehensive Guide to Atomic Structure, Schemes and Mind Maps of Chemistry

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Electron

Configurations

Electron Arrangement in an Atom

• The arrangement of electrons in an atom is its electron configuration.
• It is impossible to know where an electron is or how fast it is traveling at any given time (Heisenberg Uncertainty Principle? Walter White?).
• Models of the atom, such as the Bohr model are very inaccurate (oops!) according to modern atomic theory.
• Atoms and electrons are more

complicated than planets orbiting the Sun.

Electron Orbitals

• Orbitals are clouds of probability within an energy level, so an actual orbital is a region of space, where an electron might be found.
• Two orbital clouds are pictured below. There are more dots near the center of the picture, because an electron is most likely to be near the nucleus (center) of the atom (the electron which is negative is attracted to the positive protons).

Types of Orbitals

• Within the energy shells are different shaped orbitals (represented by the letters s, p, d, and f) that can contain different total numbers of electrons. A number can be placed in front of the orbital letter to represent the energy level that an orbital belongs to.

For example: 1s is an s shaped orbital on the 1 st energy level, which is closest to the nucleus

If a vehicle were an orbital…..

• Match the orbital to the vehicle that most represents it!

So how do the orbitals REALLY look?

Another way to look at it….

• The boxes represent the different orbitals. As the number of the level increases, the energy increases. Each individual box can hold 2 electrons at a time.

How are electrons in their orbitals like

an apartment house?

• Different floors in the apartment represent different energy levels or shells.
• Each room on each floor of the apartment house corresponds to an orbital, or one box from the previous diagram.

Who figured this out and how does it relate to the apartment analogy?!? Apartment House Rules Electron Rules From the Bottom Up : Rooms must be filled from the ground floor up. Fill the one room on the first floor before starting to put new tenants on the second floor. Then fill the s room before the p rooms. At higher floors the order might change a bit.

Aufbau Principle : the electrons fill the available orbitals from lowest energy to highest energy. In the ground state all the electrons are in the lowest possible energy level.

Singles First : the owner of the building wants to have the tenants spread out as much as possible. For that reason singles are placed in rooms before couples. If couples must be placed into a room then all of the other rooms on that floor must already have a single in them.

Hund’s Rule: The electrons must be placed into the orbitals in such a way that no pairs are put together unless absolutely necessary. That is, single electrons must be placed into boxes first and then paired up if necessary.

Opposite “Gender” Only : When two people are placed in a room they must be of opposite genders. No men may room together and no women may room together. This is an arbitrary rule on the part of the owners: in a just world we wouldn’t have to follow it. But quantum mechanics has nothing to do with justice.

Pauli Exclusion Principle : Electrons come in two varieties based on the direction they are ‘spinning’. There is an Up spin and a Down spin. Up and Down spins are always paired together and Up-Up or Down-Down combinations are not allowed. No two electrons can ever be in the same place at the same time.

The Periodic Table – A Cheat Sheet for Knowing the Order of Filling Electron Orbitals

1 (^23) 4 5 6 7

More Practice

• Fill in the electron orbitals for Si, then write out the complete electron configuration.

1s^2 2s^2 2p^6 3s^2 3p 2

Electron Configs

with Elements in the d Block

Notice that when you get to the 3d orbital, it is higher in energy than the 4s orbital. The rule is that electrons fill lower energy orbitals first, so electrons will actually fill the 4s orbital after 3p, then electrons will begin to fill the 3d orbital.

Noble Gas Notation

• This is much shorter and more convenient than writing out the entire electron configuration.
• Use the symbol for the noble gas that is just before the element you are configuring. (The noble gas and the element will have the same configuration, or inner electron structure, up to that point )
• Then complete the configuration that comes after the noble gas for the element in question.
• Example: The complete configuration for Na is 1s^2 2s^2 2p^6 3s^1. Neon is the noble gas that comes before Na on the periodic table. So the noble gas notation for Na would be: [Ne]3s^1

Practice!

• Write the noble gas notation for the following elements: - Chlorine - Beryllium

[Ne]3s^2 3p^5

[He]2s^2