9th Class Chemistry Chapter 2 Structure of Atoms Short Questions Answer

9th Class Chemistry Chapter 2 Structure of Atoms Short Questions Answer

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What is the nature of charge on cathode rays?

When these rays passed through electric field, these deflect (bend) tower positive plate showing that these are negatively charged.

Give five characteristics of cathode rays?

The characteristics of cathode rays are as under:
These rays travel in a straight line perpendicular to the cathode surface.
They raise the temperature of the body on which they gall.
Light is produced when these rays hit the sides of discharge tube.
They can cast a sharp shadow.
The nature of rays does not depend upon the nature of as used in discharge tube.

The atomic symbol of a phosphorus ion is given as (³¹₁₅P³⁻)
How many protons, electrons and neutrons are there in the ion?
What is name of the ion?
Draw the electronic configuration of the ion.
Name the noble gas which has the same electronic configuration as the phosphorus ion has.

In [³¹₁₅P³⁻] ion:
The number of protons = 15
The number of electron = 18
The number of neutrons = 16
(B) The name of the ion is.
P⁻³ is called phosphides ion.
(C) The electronic configuration of the ion. Phosphorus ion has 15 electron, so its electronic configuration is,
³¹₁₅P⁻³ = 1s², 2s², 2p⁶, 3s², 3p³
(D) Phosphorus ion [P⁻³] 18 is formed by gaining three electrons in its outermost shell, Now, it has same electronic configuration as that of noble gas element “Argon” [Ar] 18.

Differentiate between shell and subshell with examples of each?

The fixed circular orbits which is associated with a definite amount of energy is called a shell or energy level.
The shells are subdivided into subshells.
Example: K, L, M, N etc. are considered as the shells or energy levels of any atom.
Each shell composed of one or more subshells.
The sub division of a shell in an atom is called subshell.
The subshells are also themselves composed of atomic orbital.
Example: s, p, d and f are considered as the subshells of a shell.

An element has an atomic number 17. How many electrons are present in K, L and M shells of the atom?

Atomic number of an atom is considered as the “Total number proton present in the nucleus of the atom.”
If an atom has “I7” atomic number its electronic configuration will be as;
[C1] = 1s², 2s², 2p⁶, 3s², 3p⁵
K = 2-electrons
L = 8-electrons
M = 7-electrons

Write down the electronic configuration of Al³⁺. How many electrons are present in its outermost shell?

In case of simple [Ai] atom. Its electronic configuration is:
₁₃A1 = 1s², 2s², 2p⁶, 3s², 3p¹
In this case, the outermost shell is “M” ad it has three electrons in it.
While in case of [A1³⁺] ion, It has 10 electrons, so it electronic configuration is [A1³⁺] = 1s², 2s², 2p⁶
Now, the outermost shell is “L” and it has 8 electrons in it.

Magnesium has electronic configuration 2, 8, 2,
(a). How many electrons are in the outermost shell?
(b). In which subshell of the outermost shell electrons are present?
(c). Why magnesium tend to lose electrons?

(a).The atomic number of “Mg” is 12 [Mg] = 1s², 2s², 2p⁶, 3s² The outermost shell is “M” and it has only two electrons in it.
(b). the outermost electors of “Mg” are present in “s” subshell of the 3rd shell “M”.
(c) Magnesium is a electropositive metal. It can easily lose its two outer most shell and get charge (2+).

What will be the nature of charge on an atom when it loses an electron or when it gains an electron?

When an atom losses its electron, it becomes positively charged ion called cation. e.g., Metals of 1st, 2nd group when atom gains electrons it becomes negatively charged ion called anion. e.g., Halogens

For what purpose is U-235 used?

A U-235 is used to get large amount of energy which can be used to drives the turbines to generate electrician. This is the peaceful use of atomic energy for the development of a nation.

A pedant has goiter. How will it be detected?

Isotopes of iodine-131 are used for diagnosis if goiter in thyroid gland. These radioactive isotopes are used as tracers in medicine to diagnose the presence of tumor in the human body.

Give three properties of positive rays?

Positive rays are also called “canal rays”. Its properties are:
These rays travel in straight line in a direction opposite to the cathode rays.
These are positively charged rays.
Mass of these particles was found equal to that of a proton or simple multiple of it.

What are the defects of Rutherford’s atomic model?

The defects are as follows:
According to this atomic model, a revolving electron being a charged particle must radiate energy continuously. By decreasing energy, it will close to nucleus but it is known fact that the revolving electron never falls into the nucleus.
Rutherford’s model of atom also suggests that there would be in continues atomic spectrum but actually a line atomic spectrum is obtained.

As long as electron remains in an orbit, it does not emit or absorb energy. When does it emit or absorb energy?

Electrons do not emit or absorb energy till they remains in their orbits. When an electron jumps from high energy level to the lower energy level, it emits energy. E₂–E₁ = Energy emits and when an electron jumps from lower energy level to high energy level it gains energy .
E₁–E₂= Energy gain

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