# Chemistry Class 11 NCERT Solutions: Chapter 2 Structure of Atom Part 7

Q: 20. Calculate the wavelength of an electron moving with a velocity of.

According to de Broglie’s equation,

Where,

Substituting the values in the expression of λ

Hence, the wavelength of the electron moving with a velocity of

Q: 21. The mass of an electron is If its J, calculate its wavelength.

From de Broglie’s equation,

Given,

Kinetic energy (K.E) of the electron

Substituting the value in the expression of

Hence, the wavelength of the electron is

Q: 22. Which of the following are isoelectronic species i.e., those having the same number of electrons?

Isoelectronic species have the same number of electrons.

Number of electrons in sodium

Number of electrons in

A positive charge denotes the loss of an electron.

Similarly,

Number of electrons in

Number of electrons in

Number of electrons in

A negative charge denotes the gain of an electron by a species.

Number of electrons in sulphur

Hence, the following are isoelectronic species:

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