FBISE 9th Class Chemistry Chapter 2 Structure of Atoms Short Questions Answers
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Class/Subject: 9th Class Chemistry
Chapter Name: Structure of Atoms
Board: Federal Board
Helpful For:
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FBISE 9th Class Chemistry Chapter 2 Structure of Atoms Short Questions Answers
What is the nature of a charge on cathode rays?
Cathode rays are negatively charged particles. J.J. Thomson discovered the e/m (Change/mass) ratio of cathode rays and found it equal to the electron.
An element has an atomic number 17. How many electrons are present in the K, L, and M shells of the atom?
The atomic number of element = 17, Its electronic configuration will be: K L M
1S2, 2s2, 2p6, 3s2, 3p5
2 8 7
Give three properties of positive rays?
i. They travel in a straight line in a direction opposite to cathode rays.
ii. Their deflection in the electric and magnetic fields proved that these were positively charged.
iii. Mass of these particles was found equal to that of a proton or a simple multiple of it.
Define plum pudding model. Who presented it?
Atoms are solid structures of positive charge with tiny negative particles stuck inside. It is like a plum in the pudding. Thomson put forth his plum pudding theory.
Write three properties of neutrons.
i. Neutrons carry no charge
ii. They are high penetrating
iii. Mass of neutrons are nearly equal to the mass of a proton.
Write the electronic configuration of Fluorine.
9F = 1s2, 2s2, 2p5
Define isotopes?
Atoms of an element that have the same atomic number but different atomic masses are called isotopes.
Define radioactive-isotopes dating.
The age determination of very old objects based on the half-lives of the radioactive isotope is called radioactive-isotopes dating.
What is meant by radiocarbon dating or carbon dating?
This is an important method of age determination of old carbon-containing objects (fossils) by measuring the radioactivity of C-14 in them is called radiocarbon dating or simply carbon dating.
What is Dalton’s atomic theory?
According to John Dalton’s:
i. All matter is made up of very small indivisible particles called atoms.
ii. An atom is indivisible
iii. Atoms of the same element are alike
iv. They combine in different ways to form compounds.
What is meant by Quantum?
Quantum means fixed energy. It is the smallest amount of energy that can be emitted or absorbed as electromagnetic radiation. Quanta is plural of quantum.
What is the maximum number of electrons that can be accommodated in a p-subshell?
p-subshell can accommodate a maximum of six electrons.
Give five characteristics of cathode rays?
i. These rays travel in a straight line perpendicular to the cathode surface.
ii. They can cast a sharp shadow of an opaque object is placed in their path.
iii. They raise the temperature of the body on which they fall.
iv. J.J. Thomson discovered their e/m ratio.
v. Light is produced when these rays hit the sides of the discharge tube.
How many sub-shells are there in N shell?
Shell n = 4 contains 4 subshells, s, p, d, and f (4s, 4p, 4d, 4f)
What are the defects of Rutherford’s atomic model?
i. According to classical theory, electrons being the charged particles should release emit energy continuously and they should ultimately fall into the nucleus.
ii. If the electrons emit energy continuously, they should form a continuous spectrum but in fact, line spectrum was observed.
As long as an electron remains in an orbit; it does not emit or absorb energy. When does it emit or absorb energy?
The energy is emitted or absorbed only when an electron jumps from one orbit to another. When an electron jumps from a lower orbit to a higher orbit it absorbs energy and when it jumps back from a higher orbit to a lower orbit, it radiates energy. This change in energy is given by following Planck’s equation.
ΔE = E2 – E1 = hv
Where E2 = Energy of higher energy orbit
E1 = Energy of lower energy orbit
h is Planck’s constant is value is 6.63 x 10-34 Js. v is the frequency of light.
Write the use of Co-60.
Cobalt-60 emits strongly penetrating gamma rays and hence used for cancer affecting within the body.
Why does an electron first fill 2p orbital and then 3s orbital?
An electron first fills 2p orbital because the electrons fill the shells in order of their increasing energy, i.e. lower energy level is occupied first then the higher energy level. So 2p orbital has a lower energy level than 3s orbital.
What do you mean by electronic configuration?
The distribution of electrons around the nucleus in various shells and subshells according to their increasing energy is called electronic configuration.
Write down the properties of isotopes?
i. They have the same electronic configuration and number of protons.
ii. They differ in the number of neutrons.
iii. Isotopes have similar chemical properties because they depend upon electronic configuration.
iv. They have different physical properties because these depend upon atomic masses.
v. Most of the elements show isotopes.
If both K and L shells of an atom are filled what is the total number of electrons present in them?
These are 10 total numbers of electrons present in K and L shells.
What is the electronic configuration of a hydrogen atom?
The electronic configuration of a hydrogen atom is 1s-1.
Define nuclear fission reaction.
Nuclear fission reaction is the type of nuclear reaction in which an isotopic bombarded with slow-moving neutrons that isotopes of element emit three neutrons and split into same other isotopic elements.
Which of the isotopes of hydrogen contains a greater number of neutrons?
Isotopes of hydrogen tritium have a greater number of neutrons. It has 2 neutrons.
How many neutrons are present in C – 12 and C – 13?
In C – 12, there are six neutrons present and in C – 13 there are seven neutrons present in the nucleus.
Why do the isotopes of an element have different atomic masses?
Because the isotopes of an element have a different number of neutrons.
Explain how anode rays are formed from the gas taken in the discharge tube.
Anode rays do not originate from the anode. These rays are produced when the cathode rays or electrons collide with the residual gas molecules present in the discharge tube and ionize them as follows:
M + e- → M+ + 2e-
What is Classical theory?
According to classical theory, electrons being the charged particles should release or emit energy continuously and they should ultimately fall into the nucleus.
What is Quantum theory?
Quantum means fixed energy. It is the smallest amount of energy that can be emitted or absorbed as electromagnetic radiation.
What is the maximum capacity of the shell?
K shell can accommodate 2 electrons
L shell can accommodate 8 electrons
M shell can accommodate 18 electrons
N shell can accommodate 32 electrons
