How Many Valence Electrons Does Phosphorus (P) Have? [Valency of Phosphorus]

Phosphorus, a chemical element with the symbol P and atomic number 15, is an essential element for life as it is one of the major components of DNA, RNA, ATP, and phospholipids. The elemental phosphorus exists in two major forms, white phosphorus, and red phosphorus but due to high reactivity, it does not found in a free state on earth.

It oxidation states are varies from -3 to +5 (-3, -2,-1, 0, +1, +2, +3, +4, +5) and its electronegativity value is 2.19 according to the Pauli scale.

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

Phosphorus (P) Valence Electrons

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

Step 1: Find the Atomic Number

To find out the atomic number of phosphorus, we can use the periodic table. With the help of the periodic table, we can easily see that the atomic number of phosphorus is 15. As its atomic number is 15, it has 15 protons, and for neutral phosphorus, the number of protons is always equal to the number of electrons i.e. has 15 electrons in its nucleus.

Step 2: Write Electron Configuration

Electron configuration is the arrangement of electrons on the orbitals. The phosphorus atom has a total of 15 electrons so, we have to put 15 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,

Phosphorus electron configuration P (15) =  1s²2s²2p⁶3s²3p³ (complete configuration).

=  [Ne] 3s²3p³ (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]3s²3p³, the highest value of n is 3 so that the valence shell of phosphorus is 3s²3p³.

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 five electrons present in the valence shell of phosphorus (3s²3p³). Thus, phosphorus has five valence electrons.

Valency of Phosphorus (P)

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 phosphorus can reach the stable state (nearest inert gas configuration: Ar) by getting 3 electrons. So that the valency of phosphorus is 3 (trivalent).

Note: Basically, phosphorus has a stable oxidation state of +3 and +5 in compound formations so that it can forms both PCl3 and PCl5 in stable states. Do not confuse with +3 or +5, it is just an oxidation number that can vary from compound to compound. But its valency is 3 only in any case.  

In another sense, a phosphorus atom can form a maximum of three covalent bonds in chemical bonding (For example: PH3, PCl3, 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 phosphorus with the help of the periodic table. As phosphorus belongs to group 15 (5A or VA) along with nonmetal nitrogen (N), the metalloids arsenic (As) and antimony (Sb), and the metal bismuth (Bi). These group elements are also called pnictogens. All these elements have a valency of 3.