The electrons of an atom are typically divided into two categories: valence and core electrons. Valence electrons occupy the outermost shell or highest energy level of an atom while core electrons are those occupying the innermost shell or lowest energy levels. This difference greatly influences the role of the two types of electrons in a chemical reaction. Generally, valence electrons can participate in the formation of chemical bonding, but core electrons cannot. While core electrons are not involved in bonding, they influence the chemical reactivity of an atom.
Argon Valence Electrons 0 Atomic Number 18 Learn more about the atomic number. Atomic Mass 39,948 Learn more about the atomic mass. Atomic Symbol Ar State at 20 °C Gas Description Colorless, odorless, tasteless noble gas. It is the third most abundant element. (Electrons within a shell have very similar energies and are at similar distances from the nucleus.) In the chemical elements of atomic number 17 to 19, for example, the chloride ion (Cl −), the argon atom (Ar), and the potassium ion (K +) have 18 electrons in closed. Electron configuration is the arrangement of electrons on the orbitals. The argon atom has a total of 18 electrons so, we have to put 18 electrons in orbitals. The electrons will be placed in orbital according to this energy levels: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f. Name: Argon Symbol: Ar Atomic Number: 18 Atomic Mass: 39.9 Number of Protons/Electrons: 18 Number of Neutrons: 22 Classification: Noble Gases Discovery: 1894 Discoverer: Sir William Ramsay.
The electron configuration of a oxygen atom is
[ce{O}: ,1s^22s^22p^4 label{1}]
which may be shorted
[ce{O}:, [He]2s^2 2p^4 label{2}]
where the ([He]) stands for the configuration of helium ((1s^2)). Similarly, the configuration of calcium with 20 electrons can be written
[ce{Ca}:, [Ar]4s^2 label{3}]
where the ([Ar]) stands for the configuration of argon ((1s^22s^22p^6 3s^2 3p^6)). Electronic configurations that are the same as noble gases are very stable since they have a full octet (except helium with a full 1s orbital).
The (1s) electrons in oxygen do not participate in bonding (i.e., chemistry) and are called core electrons. The valence electrons (i.e., the (2s^22p^4) part) are valence electrons, which do participate in the making and breaking of bonds. Similarly, in calcium (Equation (ref{3})), the electrons in the argon-like closed shell are the core electrons and the the two electrons in the 4s orbital are valence electrons.
Example (PageIndex{1}): Cobalt
What are the core and valence electrons in cobalt?
Solution
Start by writing the electron configuration of cobalt with 27 electrons:
[1s^22s^22p^63s^23p^64s^23d^7 nonumber]
However, argon has the electronic structure (1s^22s^22p^23s^23p^6), so we can rewrite the configuration as
[[Ar]4s^23d^7 nonumber]
The Number Of Valence Electrons In Argon
The two electrons in the (4s) orbital and the seven electrons in the (3d) are the valence electrons: all others are core electrons.
The periodicity of valance electrons can be seen in the Periodic Table. Basically, the periodicity is only applied to the main group elements, while in transition metals, rules are complex.
The core electrons remain the same in the increase of group numbers in the main group elements. On the other hand, the valance electrons increase by one from left to right of a main period, and remain the same down the column of a main group. This evolution gives periodical change in property of a period, and similar chemical property of a group, which is called periodical trend. The number of valence electrons in a main period is the same as its group number. The table below shows this rule clearly.
Under construction
Figure 1: 1A + 2A are metals. 3A to 8A are non-metals.
However, this periodicity cannot be applied to the transition group, which is more complicated than that of the main group. Although the outermost electrons can be easily determined, the apparent valence electrons considered in chemical reactivity are complex and fluctuated. Electrons going into d sublevel can play either a role of valence electrons or shielding electrons. So there is not always a certain number of apparent valence electrons. The number of apparent valence electrons for the first transition metal period is shown in the table below.
Under construction
Figure 2: Valence electrons for transition metals.
Relationship with Chemical Reactivity
Atomic Number Of Argon
The chemical reactivity of an atom is mainly determined by valence electrons. Atoms which have a complete shell of valence electrons tend to be chemically inert. Atoms with one or two valence electrons are highly reactive. This phenomenon can be explained by Hund's rule, which states that orbitals that are empty, half-full, or full are more stable than those that are not. For example, Ne is chemically inert because it has two valence electrons that fill its outermost shell which makes it stable compared to atoms such as Al, which has three valence electrons, but its valence electrons does not fill its outermost shell.
Although core electrons do not take part in chemical bonding, they play a role in determining the chemical reactivity of an atom. This influence is generally due to the effect it has on valence electrons. The effect can be observed from the gradual change of chemical reactivity in a group. As you go down a group, more shells are occupied by electrons, which increases the size of the atom. The more core electron shells an atom has, the larger the size of the atom, and the farther the valence electrons are from the nucleus, thus the valence electrons will experience less effective nuclear charge and will be easily lost. For example, (ce{Na}) and (ce{K}) can both react with water, but K has a more radical reaction because it has more shells of core electrons which makes the valence electron in its outermost orbital much easier to lose than the valence electron of Na.
References
Miessler, Gary L., and Donald A. Tarr. Inorganic Chemistry. Upper Saddle River, NJ: Pearson Prentice Hall, 2010. Print.
Brown, Ian David. The Chemical Bond in Inorganic Chemistry the Bond Valence Model. Oxford: Oxford UP, 2006. Print.
What is the electron configuration of argon?
1 Answer
The electronic configuration of Argon (atomic number is 18) is-
#1s^2 2s^2 2p^6 3s^2 3p^6#
Argon Neutrons
Note:- For writing the electronic configuration of elements, the Aufbau Principle is used. In Aufbau Principle, the electrons are filled according to the increasing energy level of orbitals.
According to the Aufbau Principle, first the atomic number of element is determined (like here oxygen has atomic number 8) and then the electrons are filled in this order- 1s 2s 2p 3s 3p 4s 3d and so on.. . In 's' orbital, maximum number of filling the electrons is 2. In 'p' orbital, maximum number of filling the electrons is 6. In 'd' orbital, maximum number of filling the electrons is 10. In 'f' orbital, maximum number of filling the electrons is 14.
For example- i) The electronic configuration of Chlorine (atomic number is 17) is- #1s^2 2s^2 2p^6 3s^2 3p^5# ii) The electronic configuration of Titanium (atomic number is 22) is-