Class IX Digital Textbook - Valency & Atomic number

In the previous module, you studied the activities of the Distribution of the Electrons. In this module, we will get to know more about Valency & Atomic No.

Valency

Valency is the combining capacity of an atom, i.e. their tendency to react and form molecules with atoms of the same or different elements.

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For the atoms having valence electrons less than or equal to 4, valency is the same as that of the number of valence electrons in that atom.

For example, valency of Magnesium (2, 8 , 2) = 2

If the number of valence electrons exceeds 4, then valency = 8 – Number of valence electrons.

For example, valency of Oxygen (2, 6) = 8 – 6 = 2.

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Concept of Valency - Introduction

Concept of Valency | Atoms and Molecules

Atomic number (Z)

Atomic number of an element is equal to the number of protons present in the nucleus of an atom.

Since an atom is electrically neutral, thus a number of protons and number of electrons are equal, therefore:

Atomic number (z) = number of protons = number of electrons.

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Mass Number (A)

The total number of protons and neutrons present in the nucleus of an atom is called the mass number. It is denoted by A.

The protons and neutrons together are called nucleons.

The number of neutrons present in the nucleus of an atom is represented by N.

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What is Atomic Mass?

Atomic number & Mass number

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**Source of the videos: 1. Don't Memorise

2. FuseSchool - Global Education

PRACTICE QUESTIONS:

Q1 Will ³⁵CI and ³⁷CI have different valencies? Justify your answer.

Q2. In the atom of an element X, 6 electrons are present in the outermost shell. If it acquires noble gas configuration by accepting a requisite number of electrons, then what would be the charge on the ion so formed?

Q3. Why do Helium, Neon and Argon have zero valency?

Q4. What information do you get from Fig. 4.4 about the atomic number, mass number and valency of atoms X, Y and Z? Give your answer in a tabular form.

Valency

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Atomic number (Z)

Mass Number (A)

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CLOSURE

In the next class, we will discuss more about Isotopes & Isobars