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2016-02-11T22:56:05+05:30

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How can the valency of an element be determined if its electronic configuration is known? 

The electron configuration provides us the information about the state of an atom: whether it is stable or unstable, is it going to give electrons or take electrons, and so on. Suppose, an atom has an electronic configuration of -

2:8:1
it clearly shows that the atom is unstable. Its outermost shell is not complete. It can take 7 electrons. But, giving away one electron is much easier than that, so it will give away one electron. So, that makes the valency of the atom 1. 

Our focus should be on the valence shell and the number of electrons it has. Because the previous shells are undoubtedly filled, as each shell has to be filled with electrons as you go.

Another example -  an atom has an electronic configuration of:
2:8:7

That means this atom has a shortage of one electron. Only one electron is needed to fill the outermost shell and establish a stable form. Therefore, it takes one electron to fill its shell. This makes it valency 1.

*** Remember, valency is the number of electrons that an atom has to give away or take to get stable.  


What will be the valency of an element of atomic number 9
?

Fluorine is the only element in the periodic table which has atomic number 9. Atomic number is the number of protons in an atom, and the number of protons in a neutral atom is always equivalent to the number of electrons in that atom. Anyways, flourine has 9 electrons.  Fluorine is situated in group 7, row no. 2. The row number tells us that fluorine has 2 electron shells. 2 electrons fill the first shell. And, the rest 7 electrons go in the second electron shell. So, th electronic configuration becomes -

2:7

One more electron is needed to fill the valence shell. So, the valency is 1.

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