Noble Gas Configuration
Table of Contents
Ionization energy, electron affinity and bonds
Filled shells are particularly stable, and even half-filled shells are energetically favored. When all orbitals are completely filled, it is referred to as a noble gas configuration. This configuration is particularly stable and is therefore sought after by all elements. There are several ways to achieve the noble gas configuration:
Electron release
A cation is formed. (A → a + + e - )
For example, sodium, as an element in the first group, can easily donate an electron. It will give up its only valence electron in a chemical reaction, becoming a positively charged cation (Na + ).
Removing electrons from an atom requires energy, the ionization energy I E . The 1st ionization energy (e.g. for Na) is the energy that must be applied to remove the first electron from a neutral atom. The 2nd ionization energy is the energy that must be applied to remove the second electron from a singly positively charged ion, and so on. The ionization energy increases in the PSE from left to right and from bottom to top. The reason for this is that from top to bottom the distance of the electron from the nucleus, and thus the force of attraction, decreases. Since the atomic number increases from left to right, the electrons are incorporated into the same shell (same period!) with a similar size.
It is clear that maxima form in the noble gases because they are particularly stable. The alkali metals are found in minima because they are very reactive. The deviations in the diagram are also clear, as with Be and B or N and O. The explanation for this is provided by orbital theory. Beryllium has two electrons that completely occupy the s-orbital, making it stable. Boron also has a single p-electron, which can be lost relatively easily. This pattern can also be seen in nitrogen and oxygen. Nitrogen has a half-occupied 2p orbital, which is energetically favored. Oxygen, on the other hand, has four electrons in its 2p orbital, which is why an electron can be easily removed to form a stable half-filled 2p orbital.
The 2nd ionization energy is always greater than the 1st ionization energy. It is therefore easier to remove the first electron. When element A loses an electron, it becomes a + . This requires I E1 . To lose another electron, A + becomes A 2+ and I E2 is required. The positive sign makes it clear that energy must be applied. This table makes it clear that Na 2+ does not occur in chemical reactions because an energy of 5059 kJ/mol (= 496 kJ/mol + 4563 kJ/mol) cannot be applied. However, an energy of 2188 kJ/mol (= 738 kJ/mol + 1450 kJ/mol) can be applied in chemical reactions, so that Mg 2+ can be formed as a typical well-known ion.
Electron uptake
An anion is formed. (A + e - → A - ) Fluorine only needs to take on one electron to become a stable anion. It easily attains the noble gas configuration. The electron affinity EA, i.e. the ability to attract electrons, is important here. It usually has a negative sign, so energy is released. The electron affinity is particularly high in the elements on the right in the PSE (chalcogens, halogens), as these can easily attain the noble gas configuration by taking on one or two electrons. The radii of the halogen atoms are the smallest in their respective periods, and the attraction from the nucleus is therefore greatest. Halogen atoms also have the electron configuration s 2 p 5 . They are therefore missing one electron to achieve the electron configuration s 2 p 6 (also the electron configuration of the next noble gas in the periodic table). The filled shell achieved in the anion makes the anion stable, and the electron affinity of the halogens is therefore high. In comparison, the electron affinities are significantly smaller than the ionization energies. To add another electron to an anion A - to form A 2- always requires energy. This is necessary, for example, for oxygen and sulfur, which only occur stably in ionic solids. Through ionic bonds, the elements can also achieve the noble gas configuration. Sodium chloride can be taken as an example. The element sodium gives up an electron with an ionization energy. This creates a positively charged sodium cation. In this case, the element chlorine accepts this electron via electron affinity. This creates a negatively charged anion, the so-called chloride. This means that by forming the compound NaCl with Na+ and Cl−, both particles acquire a noble gas configuration.
I E1 : Na → + + e -
EA1: Cl + e- → Cl-
→
Na+ + Cl- → NaCl
Formation of bonds
When a bond is formed , the bonding electrons are shared. Each of the atoms forming the bond can thus achieve the noble gas configuration. In H2O there is no ionic bond between O2- ( O: [He] 2s2 2s2 2p4 ) and 2H + (H: 1s1 ) as there is not enough energy for this. The electrons in H2O are used jointly. A distinction is made between three different types of bonds. There is the ionic bond, which exists between metals in the bottom left of the PSE and the non-metals in the top right of the PSE. Covalent bonds are found between the non-metals in the top right of the PSE. There are also metallic bonds, which are preferentially formed by elements in the bottom left of the PSE. Semimetals form a diagonal dividing line between the metals and non-metals in the right-hand area of the main group elements. Semimetals include B, Si, Ge, As, Sb, Se and Te. If you would like to learn more about bindings, you can read about it here.
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