Electron Configurations

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APChem Topic 3: Electron Configurations Notes 3-2: Quantum Numbers, Orbitals and Electron Configurations Wave Nature of Electrons All

Work by De Broglie suggested that the electron also had some characteristics.

The result of all this work, coupled with the, led to the idea of 3D probability maps of where any one electron may be found at any

(These regions are known as ) Quantum Numbers In order to bring all of this theory together, the modern view of the electronic

Each shell has a quantum number associated with it. The 1 st Shell has a quantum number of 1, the 2 nd shell of 2 etc.

The number of sub-shells that are possible is equal to the principal quantum number (n) and are numbered with consecutive whole numbers

1 APChem Topic 3: Electron Configurations Notes 3-2: Quantum Numbers, Orbitals and Electron Configurations Wave Nature of Electrons All the work by Bohr suggested that the electron was a discrete particle. However this did not explain several of its properties. Work by De Broglie suggested that the electron also had some characteristics. Schrödinger developed this idea and solved wave equations to make predictions about where an electron may be found in an atom. The result of all this work, coupled with the, led to the idea of 3D probability maps of where any one electron may be found at any point in time within each of the fixed regions. (These regions are known as ) Quantum Numbers In order to bring all of this theory together, the modern view of the electronic structure of the atom involves the use of four which taken together, help to describe that structure. Each shell has a quantum number associated with it. The 1 st Shell has a quantum number of 1, the 2 nd shell of 2 etc. In each shell, the maximum number of electrons is given by where n is the quantum number. Each shell is further divided into. The number of sub-shells that are possible is equal to the principal quantum number (n) and are numbered with consecutive whole numbers starting from zero. These numbers are called the quantum numbers (l) or the angular momentum quantum numbers. In addition to the number system the azimuthal numbers are given the letters corresponding to 0, 1, 2 and 3 respectively. are spherical (soccer ball) shaped are dumb-bell (figure-eight) shaped and align themselves on x, y and z axes have more complicated shapes 1

The principle says that no one electron can have exactly the same set of quantum numbers, so since each orbital can hold a maximum of two electrons they must be distinguished between.

2 Each sub-shell is further divided into. The number of orbitals that are possible is equal to twice the azimuthal quantum number plus one (2l +1). Each orbital is given a number called the quantum number (m l). The possible values for (m l) are: Each orbital can hold a maximum of electrons. The principle says that no one electron can have exactly the same set of quantum numbers, so since each orbital can hold a maximum of two electrons they must be distinguished between. This is done using the final, fourth quantum number the quantum number (m s). It can have a value of. Traditionally, when there is a choice of magnetic quantum numbers the values are usually (but not always) chosen first and +½ is chosen as a spin quantum number before ½. 2

Orbital Filling Rules Aufbau Process: 1) Find out how many are present (Refer to the atomic number of the atom and then consider any charge present caused by the loss or gain of electrons).

3 Orbital Filling Rules Aufbau Process: 1) Find out how many are present (Refer to the atomic number of the atom and then consider any charge present caused by the loss or gain of electrons). 2) Lowest energy orbitals are filled. 3) of maximum multiplicity states that if there is more than one orbital with the same energy then one electron is placed into each orbital before any pairing takes place. Electron Configurations To determine the electron configuration of any element, follow these steps: 1) The period number shows the shell (principal quantum) number (n). When filling the orbitals, subtract one from the principal quantum number to determine the correct shell. 2) The block shows the type of orbital ( ). 3) Then add one for each element until the orbital, then sub-shell and ultimately the shell, is full. 4) Record the electronic configuration in the format; shell (principal quantum) number, block (orbital), number of electrons (as a superscript). 3

Electron Configuration Examples For example, hydrogen has one electron that is found in the s orbital in the first shell 1s 1 (pronounced one s one ) Helium has two electrons that are found in the s

4 Electron Configuration Examples For example, hydrogen has one electron that is found in the s orbital in the first shell 1s 1 (pronounced one s one ) Helium has two electrons that are found in the s orbital in the first shell 1s 2 (pronounced one s two ) Task 3a Write electron configurations for the first 36 elements. (Hydrogen to Krypton) (see next pages) NOTE: The anomalies of Cr and Cu are easy to explain once you know that a half-filled or completely filled d shell is considered to have extra stability. Hence configurations ending 4s 1 3d 5 and 4s 1 3d 10 rather than 4s 2 3d 4 and 4s 2 3d 9 are considered to be preferable. In each case one of the s electrons is promoted to the d shell to create a more stable configuration. 4

5 Task 3a 5

6 Task 3a 6

7 Noble Gas Core Method Task 3b From task 3a, you can see that writing full electron configurations can be tedious and time consuming. To simplify the process, we use the noble gas core method by writing the most recently filled (in the period above the current element) and only write the configuration from there. For example, phosphorus becomes, [Ne] 3s 2 3p 3 Since Ne is the previous noble gas to phosphorus and the following electrons are in the 3s and 3p subshells respectively. 1) Write the electronic configuration of the following elements using the noble gas core method. (a) Cu (b) Co (c) Ca (d) C (e) Ar (f) Ga 2) Write the electronic configuration of the following simple ions using the noble gas core method. (a) F 1- (b) Ca 2+ (c) S 2- (d) Na 1+ (e) Al 3+ Orbital Diagrams In these examples, arrows represent the and boxes represent the. Notice the three, 2p orbitals avoid having electrons paired until it is absolutely necessary. 7

Task 3c In the 3 rd and 4 th ways, the three 2p orbitals are broken down to show the separation of electrons within

8 Notation Summary We now have 4 ways to write electron configurations for elements such as nitrogen: 1 st way 1s 2 2s 2 2p 3 3 rd way 1s 2 2s 2 2p x 1 2p y 1 2p z 1 2 nd way [He] 2s 2 2p 3 4 th way [He] 2s 2 2p x 1 2p y 1 2p z 1 Task 3c In the 3 rd and 4 th ways, the three 2p orbitals are broken down to show the separation of electrons within the orbitals of the sub-shell. Using the blanks below complete the electronic configurations for the elements listed. 8

Paramagnetism and Diamagnetism Paramagnetic species are those that are by a magnet and are created when unpaired electrons are present in an atom.

Rydberg Equation The Rydberg equation is used to calculate the energy changes when electrons are promoted to higher energy levels and subsequently fall back to the lower energy levels.

9 Paramagnetism and Diamagnetism Paramagnetic species are those that are by a magnet and are created when unpaired electrons are present in an atom. Diamagnetic species are slightly by magnets and occur when all electrons are paired. Rydberg Equation The Rydberg equation is used to calculate the energy changes when electrons are promoted to higher energy levels and subsequently fall back to the lower energy levels. E = the energy associated with a particular quantum number, n. By calculating the energies associated with two different quantum levels and finding the difference, one can calculate the energy required to promote an electron from one level to another, or calculate the energy released when an electron falls back from a higher level to a lower level. Energy changes during transitions are proportional to. This means that if an electron is promoted from for example level 1 to level 5 in a species that has less protons in the nucleus the same transition for a species with more protons would be more difficult. This is because the in the nucleus are attracting the electron to the lower energy level and more energy is required to promote them. Consequently, a greater amount of energy is released from the species with the larger number of protons when the electron falls back to the original level. Transition Ions When forming positive ions, d block elements lose their outer electrons before any electrons. Isoelectronic Species Isoelectronic species have the same electronic configuration. 9

Electron Configuration. The electron configuration of an atom tells us how the electrons are distributed among the various atomic orbitals.

Electron Configuration. The electron configuration of an atom tells us how the electrons are distributed among the various atomic orbitals. Electron Configuration The electron configuration of an atom tells us how the electrons are distributed among the various atomic orbitals. Spin Quantum Number, m s In the 1920s, it was discovered that