Tamil
Nadu Matriculation Board
Class IX : Chemistry |
Chapter
1: Atomic Structure |
Very
Short Answers:
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Ans1.
The number of protons and neutrons present in an element is known as the mass number.
Mass number = number of proton + number of neutrons
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Ans2.
The number of protons present in the nucleus of an atom is the atomic number. Atomic number =
number of protons.
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Ans3.
According to Bohr's model electrons are arranged in circular orbits called energy levels.
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Ans4.
Rutherford's model : According to him electrons revolve the nucleus in circular
path but the laws of classical physics say that "any charged particle
that rotates in circular orbits
will lose energy continuously and fall in the center". So it does not
account for the
stability.
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Ans5.
According to Rutherford's model electrons are held together by electrostatic
attraction. The centrifugal force due to revolving electrons balance the electrostatic
force between opposite charged particles.
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Ans6.
According to Rutherford, some alpha particles are deflected by gold foil because
an atom has central positive charge which will repel positively charged alpha particle and
deflect them.
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Ans7.
The neutral particles having mass numbers equal to that of protons present inside nucleus
are known as neutron.
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Ans8.
The mass of proton is almost equal to the mass of atom since the mass of electron is
Marge. The mass of proton is equal to 1.6*10-24 grams.
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Ans9.
Canal rays are the smallest positive rays. These rays are produced when one or more
electrons are removed from a gas.
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Ans10.
The mass of proton is 1837 times greater than that of electrons. Mass of proton is
1.6´10-24
grams. Mass of electron is 1.6´10-29 grams. Mass of proton is almost equal to
the mass of atom. Mass of electron is negligible.
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Ans11. The
presence of perforations in the cathode are necessary for the
production of Positive rays.
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Ans12.
The rays consisting of positively charged particles, emitted from the
anode and deflected towards the cathode are
known as positive rays.
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Ans13.
The ratio of charge of an electron to the mass of an electron is known as e/m ratio.
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Ans14.
Negatively charged rays that are produced under very high potential of electricity and
deflected towards anode are known as cathode rays.
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Ans15.
Cathode rays are negatively charged particles which appear to emerge out
from the cathode and produce green fluorescence on any objects placed
in their path.
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Ans16.
Under very low pressure of 0.001mm gases, conduct electricity at high potential.
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Ans17.
The smallest particle of matter that can take part in a chemical reaction is known as
an atom. An atom consists of negatively charged particles called the
electrons which revolve around a central core called the nucleus
containing positively charged protons and neutrally charged neutrons.
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Ans18.
Proton - p, Electron - e, Neutrons - N
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Ans19.
Number of protons, neutrons and electrons : a) C1 17 18 17
b) C 6 6 6
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Ans20.
The mass of electron is found to be negligible. Therefore it must be that the mass of the
atom is equal to the mass of proton since proton mass is 1837 times more than the
electron.
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Ans21.
Charge of an atom is based on the numbers of electrons. If an atom loses an electron it
has positive charge if it gains an electron it has negative charge. If it has equal number
of proton and electron then the atom is neutral.
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Ans22.
The number of electrons in a shell is determined using the formula 2n2. Where n
is the energy level. For eg: K shell = 2 ´
1 ´
1 = 2 electrons.
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Ans23.
According to Bohr's model electrons are arranged and revolve round the electron
in a particular path called orbits. These are known as energy shells.
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Ans24.
Some shells in an atom are K,L,M,N etc., Formula to find the number of electrons = 2n2
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Ans25.
k = n = 1 = 2
´
1 ´ 1 = 2 electrons
l = n = 2 = 2 ´
2 ´
2 = 8 electrons
m = n = 3 = 2 ´
3 ´ 3= 18 electrons
n = n = 4 = 2 ´
4 ´
4 = 32 electrons |
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Ans26. L shell = n = 2 = 2n2
= 2´2´2 = 8 electrons.
M shell = n = 3
= 2 ´
3 ´ 3 = 18 electrons.
L shell can have 8 electrons, M shell can have 18 electrons.
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Ans27.
Principle of classical physics
It states that any charged particle revolving with acceleratory motion will lose
energy continuously and at last fall in the center.
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Ans28.
The number of positive charged proton and negative charged electron remains the same. So
atom remains neutral.
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Ans29.The
particles present inside the atom are known as sub atomic particles. They are proton,
neutron and electron..
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Ans30.
Proton - positive charge
Neutron - Neutral - no charge
Electron - Negative charge.
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