Why is the Valency of Phosphorus is 3&5 and Sulphur is 2,4&6?
Answers
Is the valency of phosphorus 5 or 3 or both?
Valency is the combining capacity of an element. It may be defined as the number of hydrogen atoms with which one atom of an element combines to form its normal hydride.
Elements like chlorine, oxygen, sulphur and nitrogen combine with hydrogen in the atomic ratios 1:1, 1:2, 1:2 and 1:3 to form their normal hydrides HCl, H2O, H2S and NH3, and so their respective valencies are 1, 2, 2 and 3.
Likewise, one atom of phosphorus combines with three atoms of hydrogen to form the normal hydride phosphene, PH3. Therefore, the valency of phosphorus is 3 only.
For metals it is more convenient to take into consideration the number of chlorine atoms with which one atom of the metal combines to form its normal chloride salt. This is because many metals do not form well-defined hydrides.
Sodium, magnesium and aluminium form NaCl, MgCl2 and AlCl3 respectively by combining with chlorine in the atomic ratios 1:1, 1:2 and 1:3, and so their respective valencies are 1, 2 and 3.
Iron forms two common chlorides FeCl2 and FeCl3, and it is said to exhibit variable valencies of 2 and 3. Similarly, chromium also exhibit valencies 2 and 3. Copper forms Cu2Cl2 and CuCl2 in the metal:chlorine atomic ratios of 1:1 and 1:2, and therefore it has variable valencies of 1 and 2.
Even though phophorus shows stable oxidation states of +3 and +5 in compound formation, its valency is only 3. It usually combines with metals to form simple binary compounds called phosphides (like Na3P, Ca3P2, AlP) in the oxidation state of +3 only. We can see that valency is numerically equal to the most common oxidation state which an element exhibits in simple compound formation, but having no positive or negative sign. In covalent compounds, the oxidation number or state is only a hypothetical or apparent charge assigned on the basis of certain conventions.
Answer
Valency is the combining capacity of an element. It may be defined as the number of hydrogen atoms with which one atom of an element combines to form its normal hydride.
Elements like chlorine, oxygen, sulphur and nitrogen combine with hydrogen in the atomic ratios 1:1, 1:2, 1:2 and 1:3 to form their normal hydrides HCl, H2O, H2S and NH3, and so their respective valencies are 1, 2, 2 and 3.
Likewise, one atom of phosphorus combines with three atoms of hydrogen to form the normal hydride phosphene, PH3. Therefore, the valency of phosphorus is 3 only.
For metals it is more convenient to take into consideration the number of chlorine atoms with which one atom of the metal combines to form its normal chloride salt. This is because many metals do not form well-defined hydrides.
Sodium, magnesium and aluminium form NaCl, MgCl2 and AlCl3 respectively by combining with chlorine in the atomic ratios 1:1, 1:2 and 1:3, and so their respective valencies are 1, 2 and 3.
Iron forms two common chlorides FeCl2 and FeCl3, and it is said to exhibit variable valencies of 2 and 3. Similarly, chromium also exhibit valencies 2 and 3. Copper forms Cu2Cl2 and CuCl2 in the metal:chlorine atomic ratios of 1:1 and 1:2, and therefore it has variable valencies of 1 and 2.
Even though phophorus shows stable oxidation states of +3 and +5 in compound formation, its valency is only 3. It usually combines with metals to form simple binary compounds called phosphides (like Na3P, Ca3P2, AlP) in the oxidation state of +3 only. We can see that valency is numerically equal to the most common oxidation state which an element exhibits in simple compound formation, but having no positive or negative sign. In covalent compounds, the oxidation number or state is only a hypothetical or apparent charge assigned on the basis of certain conventions.
Explanation:
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