How Many Valence Electrons Does Chlorine (Cl) Have? [Valency of Chlorine]

Chlorine, a chemical element with the symbol Cl and atomic number 17, is an extremely reactive element and strongest oxidizing agent as it has the highest electron affinity and third highest electronegativity according to the Pauli scale among the elements.

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

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

Difference Between Valence Electrons and Valency

Valence electrons are 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 are always definite, it cannot be varied (more or less) in any condition for a particular atom and may or may not be equal to its valency.

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

Chlorine (Cl) Valence Electrons

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

Step 1: Find the Atomic Number

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

Step 2: Write Electron Configuration

Electron configuration is the arrangement of electrons on the orbitals. The chlorine atom 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 energy level: [1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f]. Now,

Chlorine electron configuration Cl (17) = 1s²2s²2p⁶3s²3p⁵ (complete configuration).

= [Ne] 3s²3p⁵(condensed configuration).

Step 3: Determine Valence Shell

As we know, the valence shell of an atom can be found from the highest number of principle quantum numbers which are expressed in the term of n, and in [Ne]3s²3p⁵, the highest value of n is 3 so that the valence shell of chlorine is 3s²3p⁵.

Step 4: Find Valence Electrons

The total number of electrons 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.

Also Read:

• Valence Electrons & Valency of Hydrogen (H).
• Valence Electrons & Valency of Oxygen (O).
• Valence Electrons & Valency of Silicon (Si).

Valency of Chlorine (Cl)

There are many different ways to find out the valency of an atom which reflects the ability of an atom to bond with other atoms. Valence describes how easily an atom or a free radical can combine with other chemical species. The valency of an atom is determined based on the number of electrons lost, gained, or shared with another atom at the time of bond formation.

An atom is said to be 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, the valency is calculated by subtracting from eight and valency will be zero. Atoms having four outermost electrons possess both positive and negative valency, and atoms having eight outermost electrons, valency will be zero (i.e. noble gases).

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

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

Electron Configuration of chlorine (Cl) = 2, 8, 7

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

8 – 7 = 1

That’s why valency of chlorine is 1.

Note: In general, chlorine has a stable oxidation state of -1 most of the time but it can differ in some 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, a chlorine atom can form a maximum of one covalent bond in a chemical bonding (For example: HCl, CCl4, CaCl2, etc.), and that what valency is, the maximum ability to form bonds with atoms at the time of chemical bonding.

We can also find the valency of chlorine with the help of the periodic table. As chlorine belongs 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 these elements have valency one.