How Many Valence Electrons Does Oxygen (O) Have? [Valency of Oxygen]

Oxygen, a chemical element with the symbol P and atomic number 15, is a highly reactive nonmetal and a very good oxidizing agent which readily forms oxides which most of elements as well as compounds. At standard temperature and pressure, two oxygen atoms bind to form colorless, odorless diatomic dioxygen gas which constitutes 21% of the earth's surface.

O2 gas provides combustion energy during light and fire. It has a very big biological role in all living organisms in the form of aerobic cellular respiration and plays a major role in photosynthesis also. The simple formula for photosynthesis is given below:

6 CO2 (Carbon dioxide) + 6 H2O (water) + photons (sunlight) → C6H12O6 (glucose) + O2 (dioxygen)

You are here to know valence electrons of an oxygen atom, aren’t you? Don’t worry along with oxygen 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.

Oxygen (O) Valence Electrons

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

Step 1: Find the Atomic Number

To find out the atomic number of oxygen, we can use the periodic table. With the help of the periodic table, we can easily see that the atomic number of oxygen is 8. As its atomic number is 8, it has 8 protons, and for neutral oxygen, the number of protons are always equal to the number of electrons i.e. has 8 electrons in its nucleus.

Step 2: Write Electron Configuration

Electron configuration is the arrangement of electrons on the orbitals. The oxygen atom has a total of 8 electrons so, we have to put 8 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,

Oxygen electron configuration O (8) = 1s²2s²2p⁴ (complete configuration).

= [He] 2s²2p⁴ (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 [He]2s²2p⁴, the highest value of n is 2 so that the valence shell of oxygen is 2s²2p⁴.

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 six electrons present in the valence shell of oxygen (2s²2p⁴). Thus, oxygen has six valence electrons.

Also Read:

• Valence Electrons & Valency of Hydrogen (H).
• Valence Electrons & Valency of Carbon (C).
• Valence Electrons & Valency of Chlorine (Cl).

Valency of Oxygen (O)

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 oxygen can reach the stable state (nearest inert gas configuration: Ne) by getting 2 electrons. So that the valency of oxygen is 2.

Mathematically, the electronic configuration of oxygen is 2, 6. And as we know, if electrons in outermost shell exceeds from 4, it should be subtracted from 8.

Electron Configuration of oxygen (O) = 2, 6

We can see the outer most shell of oxygen has 6 electrons so, have to subtract it from 8.

8 – 6 = 2

That’s why valency of oxygen is 2.

Note: In general, oxygen has a stable oxidation state of -2 in most of the compounds but it may vary in some compounds due to the different bond stability. Do not confuse with -2, it is just an oxidation number that can vary from compound to compound. But its valency is 2 only in any case.  

In another sense, an oxygen atom can form a maximum of 2 covalent bonds in chemical bonding (For example: CO2, H2O, etc.), and that what valency is, the maximum ability to form bonds with atoms at the time of chemical reactions.

We can also find the valency of oxygen with the help of the periodic table. As oxygen belongs to group 16 (6A or VIA) along with sulfur (S), arsenic (As), and selenium (Se), tellurium (Te), polonium (Po), and livermorium (Lv). These group elements are also called chalcogens. All these elements have a valency of 2.