Do you know either formula of salt or water? Yeah! Formula of salt is NaCl and water is H2O. It was an easy question, wasn’t it? But have you ever thought what the reason for this specific formula is? How are these derived? Well, in this article we are going to discuss the answer of these questions which is ‘Valency’. Valency plays a vital role in determining the formula for compounds.
Valency is the combining capacity of an element. It is always a whole number. It has no plus or minus sign. The electrons present in the outermost shell of an atom are known as ‘Valence Electrons’. We can say valency is the number of electrons an element can lose or gain to attain stability. Valency is used to write the chemical formula of a compound. It means by valency we can know how the atoms of an element will combine with atoms of another element.
Let’s understand the valency by following examples –
1. Valency of Copper – Copper is a transition element. Most of the transition elements show variable valences. Copper shows two valences 1 and 2. If copper shows valency 1 or Cu(I) then its known as Cuperous while when its shows valency 2 or Cu(II) then its known as Cupric.
2. Valency of Nitrogen – Atomic number of nitrogen is 7. Its electronic configuration is 2, 5. So, it's clear that nitrogen has 5 electrons in its outermost shell. To complete its octet nitrogen needs 3 more electrons. By completing its octet, it will attain stability. Thus, the valency of nitrogen is 3.
3. Valency of Sodium – Atomic number of sodium is 11. Its electronic configuration is 2,8,1. So, it's clear that sodium needs to lose one electron to attain stability by completing its octet. Thus, its valency is 1.
4. Valency of Fluorine – Atomic number of fluorine is 9. Its electronic configuration is 2,7. It needs one electron to fulfill its octet and attain stability. So, its valency is 1.
5. Valency of Lithium – Atomic number of lithium is 3. Its electronic configuration is 2,1. So, it needs to lose one electron to attain stability and get electronic configuration like noble gas Helium. Thus, its valency is 1.
6. Valency of Helium – Atomic number of helium is 2. Its outermost shell is already fulfilled. So, helium is a highly stable element and doesn't react with other elements easily. It is also known as inert gas or noble gas. Thus, the valency of helium is zero.
7. Valency of Nickel – Nickel is a transition element. So, it shows variable valences. Its atomic number is 28. It has two electronic configurations [Ar] 3d84s2 or [Ar] 3d9 4s1. It shows valences 2,3 and 4 majorly.
8. Valency of phosphorus – Atomic number of phosphorus is 15. Its electronic configuration is 2,8,5. So, it needs 3 electrons to fulfill its outermost shell and attain stability. Thus, its valency is 3.
9. Valency of Scandium – Atomic number of scandium is 21. It is also a transition element but it doesn’t show variable valences. Its electronic configuration is [Ar] 3d1 4s2. So, its valency is 3.
10. Valency of Vanadium – Atomic number of Vanadium is 23. It is also a transition element which shows variable valances. Its electronic configuration is [Ar] 3d3 4s2. It shows valences 2,3,4 and 5 (majorly 5 & 4).
If we know the valency of elements, then we can easily write formulae of compounds of those elements. For example –
Formula of compound carbon tetrachloride –
Symbol C Cl
Valency 4 1
Formula of compound magnesium chloride –
Symbol Mg Cl
Valency 2 1
Formula of compound hydrogen chloride –
Symbol H Cl
Valency 1 1
Formula of compound hydrogen sulphide –
Symbol H S
Valency 1 2
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