Chlorine, achemical element with the symbol Cl and atomic number 17, is an extremely reactiveelement and strongest oxidizing agent as it has the highest electron affinity andthird highest electronegativity according to the Pauli scale among theelements.

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One of the mostcommon compounds in the chemical industry and real-life consumption constituentsodium chloride (NaCl) contains chlorine. It is used as sanitation, disinfection,antiseptics, weapons in world war I, and other so many things.

You are here toknow valence electrons of a chlorine atom, aren’t you? Don’t worry along with chlorinevalence electrons we will explain its valency also. But before that let’s havesome basic ideas about what these two terms are:

Difference BetweenValence Electrons and Valency

Valence electronsare the total number of electrons present in the outermost shell of an atom(i.e. in outermost orbital). The valence electrons for a neutral atom arealways definite, it cannot be varied (more or less) in any condition for aparticular atom and may or may not be equal to its valency.


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Valency is definedas the total number of electrons an atom can lose, gain, or share at the timeof bond formation to get a stable electronic configuration i.e. to complete anoctet. The valency of an atom can be variable in different compounds orchemical reactions due to the different bonding circumstances. Most of the timevalency varies/changes due to change in oxidation and reduction states.

Chlorine (Cl)Valence Electrons

There are foursimple steps to find out the valence electrons for chlorine atom which are:

Step 1: Find theAtomic Number


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To find out theatomic number of chlorine, we can use the periodic table. With the help of theperiodic table, we can easily see that the atomic number of chlorine is 17. Asits atomic number is 17, it has 17 protons, and for neutral chlorine, thenumber of protons is always equal to the number of electrons i.e. has 17electrons in its nucleus.

Step 2: WriteElectron Configuration


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Electronconfiguration is the arrangement of electrons on the orbitals. The chlorineatom has a total of 17 electrons so, we have to put 17 electrons in orbitals.The electrons will be placed in different orbitals according to the energylevel: <1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f>.Now,

Chlorine electronconfiguration Cl (17) =1s22s22p63s23p5(completeconfiguration).

= 3s²3p⁵(condensed configuration).

Step 3: DetermineValence Shell

As we know, thevalence shell of an atom can be found from the highest number of principlequantum numbers which are expressed in the term of n, and in 3s²3p⁵, thehighest value of n is 3 so that the valence shell of chlorine is3s²3p⁵.

Step 4: FindValence Electrons

The total number ofelectrons present in the valence shell of an atom are called valence electrons,and there are a total of seven electrons present in the valence shell of chlorine(3s²3p⁵). Thus,chlorine has seven valence electrons.

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Valency of Chlorine(Cl)

There are manydifferent ways to find out the valency of an atom which reflects the ability ofan atom to bond with other atoms. Valence describes how easily an atom or afree radical can combine with other chemical species. The valency of an atom isdetermined based on the number of electrons lost, gained, or shared withanother atom at the time of bond formation.

An atom is said tobe stable when its outermost shells have eight electrons (except H & He).If the total number of electrons in outermost shells is between one to four,the atom has positive valency and if electrons are between four to eight, thevalency is calculated by subtracting from eight and valency will be zero. Atomshaving four outermost electrons possess both positive and negative valency, andatoms having eight outermost electrons, valency will be zero (i.e. noblegases).

Elements like chlorinecan reach the stable state (nearest inert gas configuration: Ar) by getting oneelectron.So that the valency of chlorine is 1.

Mathematically, theelectronic configuration of chlorine is 2, 8, 7. And as we know, if electronsin outermost shell exceed from 4, it should be subtracted from 8. So,

ElectronConfiguration of chlorine (Cl) = 2, 8, 7

We can see the outermost shell of chlorine has 7 electrons so, have to subtract it from 8.

8 – 7 = 1

That’s why valencyof chlorine is 1.

Note: In general, chlorinehas a stable oxidation state of -1 most of the time but it can differ insome compounds with values 0 (Cl2), +1 (NaClO), +3 (NaClO2), +4 (ClO3), +5 (NaClO3),+7 (NaClO4). Do not confuse with -1 or something else (+1, +3, +4, etc.) with positive or negative signs, it is just an oxidation number that can vary from compound to compound. But its valency is always 1 in any case.

In another sense, achlorine atom can form a maximum of one covalent bond in a chemical bonding (Forexample: HCl, CCl4, CaCl2, etc.), and that what valency is, the maximum abilityto form bonds with atoms at the time of chemical bonding.

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We can also findthe valency of chlorine with the help of the periodic table. As chlorinebelongs to group 17 (17A or VIIA) along with fluorine (F), bromine (Br), and iodine(I), and astatine (At). These group elements are also called halogens. All theseelements have valency one.