Valence Electrons

Understanding Valence Electrons: Each atom or molecule has a center called a nucleus. It containing two major particles a proton and a neutron. Protons are positively charged and neutrons are electrically neutral. Electrons whirling around the nucleus are negatively charged particles. These electrons move in paths that are arranged in energy levels. The outermost energy level is most stable when it contains eight electrons.

Whether an element combined to form a compound or not depends on the arrangement of electrons in the outermost energy level. If this outermost energy level is completely filled with electrons, the element is chemically stable and will not bond.

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Valence Electrons Definition

The electrons present in the outermost shell of an atom are called the valence electrons. Chemists call the electrons in this outermost energy level as valence electron. Scientists use a dot diagram to represent the number of electrons present in an atom’s outermost energy level.Valence Electrons

Why are valence electrons important?

The chemical properties of elements depend on the outermost electron present. Noble gases like neon, argon and other noble gases have its full number eight electrons in its outermost energy level. This causes all the noble gases to remain inert and chemically stable.

Element Electronic Config. Shells 
 He  1s2  2
Ne [He] 2s2sp6 2,8
Ar [Ne] 3s23p6 2,8,8
Kr [Ar] 3d104s24p6 2,8,18,8
Xe [Kr] 4d105s25p6 2,8,18,18,8
Rn [Xe] 4f145d106s26p6 2,8,18,32,18,8

Valence Electrons Periodic Table

Henry Moseley put forward the modern periodic law, which states that the properties of elements are the periodic functions of their atomic number. That is, if the elements are arranged in tabular form in the increasing order of their atomic numbers, then the properties of the elements are repeated after definite regular intervals or periods.

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Niel Bohr gave the extended form of the table known as the long form of the periodic table or modern periodic table. A tabular arrangement of elements in groups (vertical column) and periods(horizontal rows) highlighting the regular trend in properties of elements is called a periodic table.

All elements in the periodic table except noble gas have electron between one and seven in their outermost energy level. In order to fill their outer energy levels, these elements will gain lose or sometimes share electrons and by doing so form chemical bonds.

Valence Electron In Groups and Period

The valence electron varies as we move across period and groups.

  1. Outermost electron of the representative elements (S and P block) in a period increase.Valence Electrons
  2. The number of valence electron remains same down the group. let see the valence electron of elements of each group one by one.
Representative Elements Group
S block Valence electron
P block 10 + Valence electron


Elements Shells Electron Group
Na  2,8,1 1
Mg  2,8,2 2
B 2,3 10+3 =13
K 2,8,8,1 1
P 2,8,5 10+5 =15
S 2,8,6 10+6 =16
  • In Alkali metal group, each element in this group contains one electron in its valence shell. Hence, these are kept in Group one of the periodic table.
  • Similarly, the elements of the alkaline earth metal group have two electrons in their outermost shell and are kept in group two.
  • The elements of boron group family have three outermost electron and the elements of carbon family Group have four outermost electrons.
  • Nitrogen family Group has five outermost electrons.
  • Oxygen, Halogen and Noble gas family Group has 6,7,8 outermost electron respectively.

Carbon Valence Electrons

Electronic Config.  Electrons Group/Period/block 
[He] 2s2 2p2 2,4 14/2/p-block.

Neon Valence Electrons

Electronic Config. K,L Group/Period/block 
[He]2s22p6 2,8 18/2/p-block.

Valence Electron of Oxygen

Electronic Config. K,L Group/Period/block 
[He]2s22p4 2,6 16/2/p-block.

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