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Valence Electrons

A chemical element is a pure chemical substance which consists of one type of atom. All elements can be distinguished from their different chemical and physical properties.

Each atom has a certain atomic number which decides almost all properties of an atom. As the atomic number is the number of protons in an atom which must be equals to the number of electrons in an atom.

In an atom, proton and neutron located at the center of atom called as nucleus, while negatively charged particles, electrons circulate around nucleus in certain paths known a orbits. These orbits can be considered as shell around nucleus in an atom. Each shell contains a certain number of electrons that is 2n2 where n represents the number of shell. Shells in an atom can be represents by “K, L, M...”.
  1. K shell= 1st shell, contain 2 electrons
  2. L shell= 2nd shell, contain 8 electrons
  3. M shell = 3rd shell, contain 18 electrons and so on.

 

Valence Electrons Definition

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In an atom, electrons filled in different levels according to their energies. First electrons filled in low energy levels and then move to higher energy level.
The outermost energy level in an atom is called as valence shell and electrons placed in this shell are known as valence electrons. These electrons are mainly in the bond formation and chemical reaction with other atoms. Therefore valence electrons are responsible for different chemical and physical properties of an element.
For example, Atomic number of magnesium is 12, therefore electronic configuration will be 1s22s2p63s2. There are three shells, out of that third shell consist of two electrons. Hence 3s is the valance shell and electrons in this shell are valence electrons of Mg. Similarly there are seven valence electrons in bromine (Br = 1s22s2p63s2p6d104s2p5).

It is more complex to determine the number of valence electrons in some elements like copper. The atomic number of copper is 29 with electronic configuration 1s22s2p63s2p6d104s1). Here no doubt electrons fill in penultimate shell but there is only one electron in valence shell that is 4s.

Valence Electrons
The long form of periodic table is based on the concept that “chemical and physical properties of elements are periodic function of their atomic number”. In periodic table, all elements are arranged in increasing order of their atomic number. There are eighteen vertical columns (groups) and seven horizontal rows (periods). In a group, all elements have same number of valence electrons only the number of shell increases by one. For example; in group-1 from lithium to Francium, the valance shell changed from 2s to 7s.

Valence Electrons Group
Group number in periodic table can be relates with the valence electrons. For s-block elements, group number is equals to number of valence electrons. For p-block elements, the number of valence electrons is equals to group number-10 (G-10). 

Valence Electrons Periodic Table Group
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Valence Electrons Chart

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Different elements with their valence electrons are follows.

Valence Electrons Chart
Periodic Table Valence Electrons 
                          
Element
Number of valence electrons
Type of bond formed Type of element
Sodium  1 (-7)
Ionic (Donates electron)
Metal
Chlorine 7 (-1)
Ionic and covalent (accepts electron)
Non- metal
Beryllium 2 (-6)
Ionic (Donates two electrons) Metal
Phosphorus 5 (-3)
Ionic and covalent (Accepts  three electrons )
Non- metal
Aluminium 3 (-5)
Ionic (Donates electron)
Metal
Silicon 4 (-4)
Covalent   Non - metal
Sulfur      6 (-2)    Ionic (Accepts electron) Non - metal
Calcium 2 (-6)
Ionic (Donates electron) Metal
Arsenic 5 (-3) Ionic and covalent (Accepts electron) Non - metal
Bromine 7 (-1) Ionic and covalent (Accepts electron)
Non - metal

Periodic Table with  Valence Electrons

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S and p-block elements show a relation between valence electrons and their position in groups and periods of periodic table. Valence electrons for alkali metals, alkaline earth metal and p-block element in periodic table are as follows.

Periodic Table with Valence Electrons
However for d- and f-block elements, the last electron filled in penultimate and ultimate shell, therefore its complex to determine their position in periodic table on the basis of valence electrons in a particulate element. Some d-block element with their valence shell configuration with apparent valence electrons is as follows.

Valence Configuration Electrons

Carbon Valence Electrons

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Carbon consist of six protons and six electrons, therefore the atomic number of element is six and located in 14th group of periodic table. The electronic configuration of carbon is 1s22s2p2. There are total four outermost shell electrons filled in second shell, hence second shell has to consider as valence shell and electrons are known as valence electrons. All these valence electrons can take part in bonding as well as in chemical reactions with other molecule; therefore the valency of carbon is four.

Carbon Valence Electrons

Oxygen Valence Electrons

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The atomic number of oxygen is 8 and it placed in 16th  group of periodic table. The electronic configuration of oxygen is 1s22s2p4. Valence shell consists of six electrons, therefore all these six electrons are valance electrons. 

Oxygen Valence Electrons

Out of these six electrons; 2s electrons are known as lain pair of electrons and generally not involve in bonding but effect the reactivity of molecules. 2p electrons take part in chemical bonding and reaction with other molecules.

Nitrogen Valence Electrons

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Just like oxygen, nitrogen also placed in second period of periodic table before oxygen as the atomic number of nitrogen is seven with electronic configuration 1s22s2p3. The second shell is outermost or valence consists of five electrons. 

Nitrogen Valence Electrons

Therefore there are five valance electrons in nitrogen atom. Due to this, nitrogen atom require three electrons to complete its octet in its valance shell and form three chemical bonds with other or same atom like in nitrogen molecule, two nitrogen atoms are bonded with three sigma bonds.
More topics in Valence Electrons
Non Bonding Electrons Bonding Electrons
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