Rule and Principle of Electrons Help (page 2)
While some scientists were studying the energy levels as element energy increased, Friedrich Hund worked on figuring out the lowest energy that electrons could be arranged in a subshell.
Hund's rule states that all orbitals of a given sublevel must be occupied by a single electron before pairing begins.
A simple example is carbon, atomic number (Z) = 6, orbital configuration of 1s 2 2s 2 2p 2 :
A more complex example is vanadium, a metal additive to steel, with an atomic number (Z) = 23, orbital configuration of 1s 2 2s 2 p 6 3s 2 p 6 d 3 4s 2 :
Quantum State Of Electrons
The Austrian physicist, Wolfgang Pauli, won the Nobel Prize for Physics for his exclusion principle; that no two electrons can have the same quantum state (position, momentum, mass, and spin) simultaneously.
The Pauli exclusion principle states that no two electrons in the same atom can be in the same configuration at the same time.
Since each orbital can only have two electrons and those must be opposite in charge (or spin), then there are only two possible values for m s . Look at the examples on the next page. Are all the orbital diagrams possible?
Did you get (a) yes, (b) no, (c) yes, (d) no, and (e) no?
In 1921, two scientists, Otto Stern and Walter Gerlach, experimenting with silver atoms and a specially designed magnet found that electrons act like tiny magnets themselves. Figure 6.5 shows how. By sending a beam of atoms through a magnet, the beam is split into two beams, one bending one way and the other bending the other way. They decided that the electrons must be attracted and repelled by opposite and like charges just like magnets attract and repel opposite and like charges. This was called spin magnetism .
This example shows an orbital diagram of electrons in the s and p orbitals.
The electrons in orbital diagrams are written as up and down arrows for (up) m s = +1/2 and (down) m s = -1/2. Electrons spinning through their orbitals act like spinning marbles of electrical charge. This spinning electrical charge circulates in the orbitals creating mini magnetic fields. This spin magnetism value is written as m s .
Additionally, just as opposites charges attract and like charges repel, so it is with pairs of electrons in orbital subshells. Two electrons with the same spin cannot be placed in orbitals together. If one electron is spinning positively, then the other must be spinning negatively.
Subshells And The Periodic Table
The Periodic Table helps chemists write the atomic makeup of a molecule fairly simply. The arrangement of a main group element uses the following formula:
n s a n p b
where n = the outer shell number and period (row) of the element and a + b = total number of valence electrons that you can get from the group (column) number.
In general, groups IA and IIA fill the s subshell, groups IIIA-VIIIA fill the p subshell, and groups IIIB- VIIIB fill the ( n - 1) d subshell.
Using the period and group information of the Periodic Table, what is the configuration of phosphorus (P), atomic number Z = 15?
Start with the first subshell on the Periodic Table as 1s, then in the second period (row) you have 2s. Jumping across in the same row is 2p. In the third period, there is 3s, 3p. In the fourth period there is 4s, 3d, and 4p.
1s 2 (first period) 2s 2 2p 6 (second period) 3s 2 3p 3 (third period) Phosphorus is in period 3 so n = 3 and group 5A so valence electrons = 5 (Remember, the valence electron shell arrangement is the same as the outermost placement of electrons.)
Try nickel (Ni), atomic number Z = 28. First consult the Periodic Table for the period number and group. Then start building the subshells. Did you get 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 8 ? This can also be written with the subshells grouped together as 1s 2 2s 2 p 6 3s 2 p 6 d 8 4s 2 .
If cesium (Ce) has a configuration of 1s 2 2s 2 p 6 3s 2 p 6 d 10 4s 2 p 6 d 10 5s 2 p 6 6s 1 what is its period number and group? What is the filling valence subshell?
Cesium is an alkali metal in period 6 and group 1. The filling orbital is 6s 1 .
It is important to remember that electrons of different elements in the same groups look the same with the exception of different orbital configurations. Members of the same family have identical valence electron structures, when considering numbers of paired and unpaired valence electrons. These similar valence structures make it possible for family group members to react similarly.
Additionally, the elements with the most orbitals, further and further out from the nucleus, become increasingly more reactive as the electrons zip through a larger area. They have more "party room" to come in contact with other atoms and they take advantage of it!
The period of an element also describes patterns. If you look at the elements from left to right in the Periodic Table along any row
The ionization energy of an element is the energy needed to detach an electron from an atom of an element.
Regular property changes can be compared to changes in electron arrangement. The higher the number of electrons in the outermost shell of an atom, the higher the ionization energy of that atom.
The elements are listed in rows so that it is easy to find information quickly. For example, if you were interested in a specific element, you would check out its place in the Periodic Table. Who are its neighbors on the chart? Which group is it in? Which period? How many electrons are in its outermost orbit (sometimes called outermost shell)? Is it reactive or not? Is it a metal or non-metal? Look again at Figure 6.4. All the group and period information that you will need on the elements can be found on the Periodic Table.
Knowing the reactivity of an element is important. If the element to be studied was potassium and you put it into water, you would have a wild reaction since alkali metals get really crazy in water. They give off hydrogen gas that ignites with the heat of the reaction and gives off a violet flame, like a lot of mini-fireworks. From potassium's soft solid state and its low boiling point, you might think it is a mild-mannered element. However, the reactive heat from an encounter with water changes a solid chunk of potassium into a liquid by melting it. Can't judge an element by its cover!
Practice problems for these concepts can be found at – Electron Configuration Practice Test
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