2 marksShort AnswerSection A

How can the valency of an element be determined if its electronic configuration is known ? What will be the valency of an element of atomic number 9 (nine) ?

Q: How can the valency of an element be determined if its electronic configuration is known ? What will be the valency of an element of atomic number 9 (nine) ?

1. **Determination of Valency from Electronic Configuration:** - Valency is determined by the number of valence electrons (electrons in the outermost shell) of an atom. - If the number of valence electrons is $1, 2, 3,$ or $4$, the valency of the element is equal to the number of valence electrons. - If the number of valence electrons is $5, 6, 7,$ or $8$, the valency is calculated as: $\text{Valency} = 8 - \text{Number of valence electrons}$. 2. **Valency of Element with Atomic Number 9:** - The electronic configuration of an element with atomic number 9 is $2, 7$. - Since the number of valence electrons is $7$ (which is greater than $4$), its valency is calculated as: $$\text{Valency} = 8 - 7 = 1$$

Metals and Non-metals

Valency and Electronic Configuration

Official Answer

Determination of Valency from Electronic Configuration:

Valency is determined by the number of valence electrons (electrons in the outermost shell) of an atom.
If the number of valence electrons is $1, 2, 3,$ or $4$ , the valency of the element is equal to the number of valence electrons.
If the number of valence electrons is $5, 6, 7,$ or $8$ , the valency is calculated as: $\text{Valency} = 8 - \text{Number of valence electrons}$ .

Valency of Element with Atomic Number 9:

The electronic configuration of an element with atomic number 9 is $2, 7$ .
Since the number of valence electrons is $7$ (which is greater than $4$ ), its valency is calculated as:

$\text{Valency} = 8 - 7 = 1$

valence electronsoutermost shellelectronic configurationoctetvalency8 minus

Marking Scheme

11 mark
21 mark

Hint

First write the distribution of electrons in shells ( $K, L, M...$ ) for atomic number 9. If the outermost shell has more than 4 electrons, subtract that number from 8 to find the valency.

Quick Oral Answer

Valency is the combining capacity of an atom. For an element with atomic number 9, the electronic configuration is $2, 7$ . Since it needs $1$ electron to complete its octet, its valency is $1$ .

Analysis & Explanation

Valency represents the number of electrons an atom needs to gain, lose, or share to achieve a stable, fully-filled outermost shell (octet rule). For elements with $1$ to $4$ valence electrons, it is energetically easier to lose these electrons to achieve a stable configuration, so their valency matches their valence electron count. For elements with $5$ to $7$ valence electrons, it is easier to gain electrons to complete their octet, making their valency equal to $8$ minus the number of valence electrons.

Common Mistakes

1Writing the valency of atomic number 9 as 7 instead of 1 by confusing valence electrons with valency.
2Not explaining the general rule of determining valency for both metals (valence electrons $\le 4$ ) and non-metals (valence electrons $> 4$ ).

Interesting Facts

The element with atomic number 9 is Fluorine, which is the most chemically reactive and electronegative of all elements.

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Frequently Asked Questions

How many marks does this question carry in CBSE Class 10 Science 2012?

This question carries 2 marks in the CBSE Class 10 Science 2012 examination.

Which chapter does this question come from in Science?

This question is from the chapter "Metals and Non-metals" in the CBSE Class 10 Science syllabus.

What topic does this question cover in Science?

This question covers the topic "Valency and Electronic Configuration" from CBSE Class 10 Science.

What type of question is this in the CBSE Class 10 Science 2012 paper?

This is a Short Answer question from Section A in the CBSE Class 10 Science 2012 paper.