Oxygen, a chemicalelement with the symbol P and atomic number 15, is a highly reactive nonmetaland a very good oxidizing agent which readily forms oxides which most ofelements as well as compounds. At standard temperature and pressure, two oxygenatoms bind to form colorless, odorless diatomic dioxygen gas which constitutes21% of the earth"s surface.
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O2 gas providescombustion energy during light and fire. It has a very big biological role inall living organisms in the form of aerobic cellular respiration and plays a major role in photosynthesis also. The simple formula for photosynthesis isgiven below:
6 CO2 (Carbon dioxide)+ 6 H2O (water) + photons (sunlight)→C6H12O6(glucose) + O2 (dioxygen)
You are here toknow valence electrons of an oxygen atom, aren’t you? Don’t worry along with oxygenvalence 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.
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.
Oxygen (O) ValenceElectrons
There are foursimple steps to find out the valence electrons for oxygen atom which are:
Step 1: Find theAtomic Number
To find out theatomic number of oxygen, we can use the periodic table. With the help of theperiodic table, we can easily see that the atomic number of oxygen is 8. As itsatomic number is 8, it has 8 protons, and for neutral oxygen, the number ofprotons are always equal to the number of electrons i.e. has 8 electrons in itsnucleus.
Step 2: WriteElectron Configuration
Electronconfiguration is the arrangement of electrons on the orbitals. The oxygen atomhas a total of 8 electrons so, we have to put 8 electrons in orbitals. Theelectrons 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 electronconfiguration O (8) =1s22s22p4(completeconfiguration).
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
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 six electrons present in the valence shell of oxygen (2s²2p⁴).Thus,oxygen has six valence electrons.
Valency of Oxygen (O)
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 oxygencan reach the stable state (nearest inert gas configuration: Ne) by getting 2electrons.So that the valency of oxygen is 2.
Mathematically, theelectronic configuration of oxygen is 2, 6. And as we know, if electrons inoutermost shell exceeds from 4, it should be subtracted from 8.
ElectronConfiguration of oxygen (O) = 2, 6
We can see the outermost shell of oxygen has 6 electrons so, have to subtract it from 8.
8 – 6 = 2
That’s why valencyof oxygen is 2.
Note: In general, oxygenhas a stable oxidation state of -2 in most of the compounds but it may vary insome compounds due to the different bond stability. Do not confuse with -2, itis just an oxidation number that can vary from compound to compound. But its valencyis 2 only in any case.
In another sense, anoxygen 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 bondswith atoms at the time of chemical reactions.
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We can also findthe valency of oxygen with the help of the periodic table. As oxygen belongs togroup 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.