What Are Valence Electrons?
According to the Bohr model, electrons revolve around the atomic nucleus in fixed orbits or shells. These shells, commonly known as electron shells, are imaginary paths where electrons are supposed to orbit. These shells are arranged in increasing order or energy levels, starting from the closest to the nucleus.
The electron shell or energy level farthest from the nucleus is referred to as the valence shell. The electrons residing in the valence shell are called valence electrons.
In simple terms, the atom’s outermost electron shell is known as valence shells, and the electrons found there are termed valence electrons. To be more precise, the number of electrons present in the outermost shell of an atom that takes part in any chemical reaction by forming bonds are called valence electrons.
Atoms are most stable if they possess a filled valence shell of electrons, i.e., 8 electrons in their valence shell, octet state. An exception to this phenomenon is hydrogen and helium that become stable with 2 electrons in their outermost shell, duplet state.
How To Find The Number Of Valence Electrons In An Element?
The classical method of finding the number of valence electrons in an element would be to count the number of electrons in its last shell. Nevertheless, it is a laborious task. Scientists have made this task easier by arranging the elements in the periodic table. Another way to determine valence electrons is by knowing the electronic configuration of that element.
1. Using Periodic Table
In order to determine the number of valence electrons of an element, we only have to refer to the periodic table and search for the position of the element in it. As we move from top to bottom of a group, the number of valence electrons remains the same, although the number of shells increases. On the contrary, the number of valence electrons across a period increases by one, as we move from left to right of a period.
Exception: As discussed, the period number indicates the number of shells, whereas the group number indicates the number of valence electrons in the outermost shell. However, this only holds true for the main group elements, groups 1-2 and 13-18. The rule is inapplicable to the transition and inner transition element, groups 3-12.
Valence Electrons Periodic Table Chart
The table below shows the number of valence electrons in the different groups of the periodic table:
|Periodic Table Group||Valence Electrons|
|Group 1 (I) – Alkali metals||1|
|Group 2 (II) – Alkaline earth metals||2|
|Group 13 (III) – Boron group||3|
|Group 14 (IV) – Carbon group||4|
|Group 15 (V) – Nitrogen group||5|
|Group 16 (VI) – Oxygen group||6|
|Group 17 (VII) – Halogens||7|
|Group 18 (VIII or 0) – Noble gases||8|
2. Using Electronic Configuration
Within the shells, electrons occupy a special place, called atomic orbitals. The arrangement of electrons in these orbitals is known as electronic configuration. The configuration of electrons gives a quick overview of the number of electrons present in the last shell. So, just by writing the electronic configuration of that element, we can quickly determine its number of valence electrons.
Here is a table showing the number of valence electrons of elements belonging to the second period, along with their electronic configuration.
|Name of the element||Symbol||Atomic Number||Electron Configuration||No. of valence electrons|
Characteristics of Valence Electron
- The valence electrons exist only in the outermost electron shell for the main group elements. On the other hand, they can exist in the inner shell for a transition metal.
- An atom having a fulfilled octet or duplet will become chemically inert.
- They can either absorb or release energy in the form of a photon.
- They also determine the electrical conductivity of an element. Depending on this property, elements can be categorized as metal, non-metal, or metalloid.
Representing Valence Electrons In Lewis Symbols
Lewis structure is a simplified representation of the valence shell electrons in a molecule. Here, the atom is represented using a special symbol called the Lewis symbol.
In the symbol, first, the element’s chemical symbol is written, and then its valence electrons are represented as dots surrounding it. Only the electrons residing in the valence shell are represented here as the chemical reactivity of an atom is solely determined by the number of its valence electrons and not its inner electrons.
For instance, the Lewis symbol of oxygen depicts a ‘O’ surrounded by 6 valence electrons because oxygen has an electron configuration of 1s22s22p4.
Article was last reviewed on Thursday, December 2, 2021