The valency of phosphorus is ________.
3, 5
Understanding Phosphorus Valency
Phosphorus (\(P\)) is a fascinating element found in Group 15 of the periodic table. Its chemical properties, especially its valency, are key to understanding its compounds.
Valency refers to the combining capacity of an element, which is determined by the number of electrons in its outermost shell and how it participates in chemical bonding.
Electronic Configuration and Valency of Phosphorus
The electronic configuration of phosphorus is \([Ne] 3s^2 3p^3\). It has 5 valence electrons in its outermost shell (the third shell).
Phosphorus commonly exhibits different valencies by:
- Gaining or sharing 3 electrons to achieve a stable octet configuration (\(3s^2 3p^6\)).
- Sharing all 5 valence electrons.
- Expanding its octet using vacant \(3d\) orbitals.
Common Valencies of Phosphorus: 3 and 5
Let's look at the common valencies phosphorus shows in its compounds:
-
Valency 3: Phosphorus can achieve a stable octet by sharing 3 electrons. This leads to a valency of 3. A common example is phosphorus trichloride (\(PCl_3\)), where phosphorus forms three single covalent bonds with chlorine atoms.
\[PCl_3\]
-
Valency 5: Unlike elements in the second period (like Nitrogen), phosphorus, being in the third period, has access to vacant \(3d\) orbitals. This allows it to accommodate more than 8 electrons in its valence shell (octet expansion). Phosphorus can use all 5 of its valence electrons (\(3s^2 3p^3\)) for bonding, resulting in a valency of 5. A classic example is phosphorus pentachloride (\(PCl_5\)), where phosphorus forms five single covalent bonds with chlorine atoms.
\[PCl_5\]
Therefore, the common valencies of phosphorus are 3 and 5.
Comparing this with the given options:
- Option 1: 2, 3 - Incorrect
- Option 2: 3, 4 - Incorrect
- Option 3: 4, 5 - Incorrect
- Option 4: 3, 5 - Correct
The valency of phosphorus is commonly observed as 3 and 5.
Revision Table: Phosphorus Valency Key Points
| Valency | Explanation | Example Compound |
|---|---|---|
| 3 | Forms 3 covalent bonds to achieve octet | \(PCl_3\), \(PH_3\) |
| 5 | Forms 5 covalent bonds (uses 3d orbitals, octet expansion) | \(PCl_5\), \(P_4O_{10}\) |
Additional Information: Factors Affecting Phosphorus Valency
While 3 and 5 are the most common valencies, phosphorus can also exhibit other oxidation states and effective valencies depending on the compound and bonding environment. For instance, in phosphine oxides, phosphorus can form a double bond with oxygen, exhibiting a total of 5 bonds (4 sigma and 1 pi), contributing to its overall bonding capacity in that molecule.
The ability to exhibit multiple valencies makes phosphorus a versatile element in forming a wide range of compounds, from simple phosphides to complex organophosphorus compounds.
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