This post explains the answers of questions of worksheet 5 taken from science and technology class 10.
NIOS
Class 10 Science (212) Worksheet 5 Solutions
Q1.
Look at the figure carefully:
a. What does this figure show?
b.Who has
done this experiment?
c. Explain this experiment in detail.
Answer
a. This
figure shows Goldstein’s experiment on the discovery of positive rays (canal
rays) using discharge tube with a perforated cathode.
b. This
experiment was done by Goldstein in 1886.
c. Explanation:
Apparatus
1.Discharge tube containing gas at low pressure
2.Perforated cathode
3.Anode
4. High voltage source
Procedure
When
a high voltage is applied to the electrodes, electric discharge occurs in the tube.
Goldstein observed rays moving from anode to cathode. These rays passed through
the holes in perforated cathode. These rays struck the glass wall and produces
faint red glow.
Observation: These rays were made of
positively charged particles.
Conclusion:
The particles are called protons. These rays travel in straight line and much
heavier than electrons.
Q2.
Write the electronic configuration of the elements having 12,14,19,23 and 26
protons in their nucleus.
Answer
We
have given number of protons.
Number
of protons = Atomic number (Z)
|
No.
of protons (Z) |
Element
|
Electronic
configuration |
|
12 |
Mg
|
2,8,2 |
|
14 |
Si
|
2,8,4 |
|
19 |
K
|
2,8,8,1 |
|
23 |
V
|
2,8,11,2 |
|
26 |
Fe
|
2,8,14,2 |
Q3.
Explain the plum pudding model of the atom.
Answer
The
plum pudding model of an atoms was proposed by J.J. Thomson.
According to this model:
1.The
atom is positively charged sphere in which electrons are embedded like plums in
pudding or seeds in watermelon.
2. The
total positive charge is equal to the total negative charge.
3. No
nucleus is present in atom.
4.Atom
is neutral.
Limitations:
1.This
model could not explain how electrons are arranged and move in atom.
Q4.
In what way are the different atomic particles arranged
in the atom? Explain it with reasons.
Answer
An
atom has three subatomic particles –(i) Protons (ii) Electrons (iii) Neutron
An
atom has a nucleus and shells (energy levels)
Protons(+
ve charged particles) and neutrons(no
charge) are present in the nucleus and mass of atom is concentrated in the nucleus.
Electrons
are negatively charged particles and revolve around the nucleus in shells or
energy levels (K, L, M,).
Reasons
1.Protons
in the nucleus attract electrons due to opposite charge which keep electrons
bound to atom.
2.Electrons
revolve in certain energy levels and do not radiate energy.
Q5.
A helium atom has 2 electrons in its outermost
shell but its valency is 0. Explain.
Answer
A helium atom has atomic number 2, it
means it has 2 protons and 2 electrons.
Helium has one shell K which can hold maximum
2 electrons. Due to completely filled K shell, helium is stable. So, helium does
not need to gain or lose electrons or share electrons to achieve stability.
That’s why its valency is 0.
Q6.“The number of protons and electrons in an atom and its
corresponding ions are different”. Justify this statement by using knowledge of
the atomic structure.
Answer
We
know an atom is a neutral because number of protons is equal to the number of
electrons. Protons are present in the nucleus and their number determines the
atomic number. Electrons revolve around the nucleus in shells.
When
an atom loses or gains electrons, it becomes cation (+ve ions) or anion (- ve ions).
1. When
an atom loses one or more electrons, it becomes cation.
Example
Sodium atom has 11 protons and 11
electrons. When it loses one electron, it becomes Na cation
Na
= 11 Protons, 11 electrons
Na+
= 11 Protons, 10 electrons
2.When
an atom gains one or more electrons, it becomes anion.
Example
Chlorine atom has 17 Protons and 17
electrons. When it gains one electron, it becomes Cl- ion.
Cl= 17 Protons, 17 electrons
Cl- =17 Protons, 18 electrons
The number of protons in an atom and its
corresponding ions remains same but number of electrons changes.
Q7.
If the atom of an element has 6 electrons in the
outermost shell. Can it be considered a noble gas if it accepts 2 electrons? Comment.
Answer
An
atom with 6 electrons in the outermost shell belongs to group 16. According to
octet rule, the outermost shell can hold maximum 8 electrons.
If the atom accepts 2 electrons in the outermost
shell, it achieves stable electronic configuration of a noble gas.
Example
Oxygen
(2,6) atom gains 2 electrons and becomes O2- ion (2,8). Now it has
same electronic configuration as Neon.
After achieving stable configuration, these
elements cannot become noble gas, because they are in ion form and again lose
electrons.
Q8.
“Noble gases such as Argon, Neon, Xenon are
unreactive”. Give reason in support of your answer.
Answer
Noble
gases Argon, Neon and Xenon ae unreactive or inert because they have completely
filled outermost shell and have stable electronic configuration.
He
= 2
Ne
= 2, 8
Ar
= 2,8,8
They
do not gain, lose or share electrons and take part in any chemical reaction.
Q9.
Calculate the number of protons, electrons and
neutrons in Chlorine, Bromine, Iodine, Phosphorus, Silver and Gold. Also mention
their atomic number and atomic mass (mass number).
Answer
We
know that
1.Atomic
number (Z)= number of protons = number of electrons
2. Mass
number(A) = Number of protons + number of neutrons
3.Number
of neutrons = Mass number(A) – Atomic number(Z)
|
Element
|
Atomic
number(Z) |
Mass
number (A) |
Number
of protons |
Number
of electrons |
Number
of neutrons |
|
17 |
35 |
17 |
17 |
18 |
|
|
Bromine |
35 |
80 |
35 |
35 |
45 |
|
Iodine |
53 |
127 |
53 |
53 |
74 |
|
Phosphorous |
15 |
31 |
15 |
15 |
16 |
|
Silver |
47 |
108 |
47 |
47 |
61 |
|
Gold |
79 |
197 |
79 |
79 |
118 |
Q10.
Is there any old thought about valency? If yes,
what is the new concept of valency. Give reasons in support of your answer.
Answer
Old
concept of valency: The combining capacity of an element
with hydrogen or oxygen is known as valency.
New
concept of valency: The tendency of an atom of an element can gain, lose or share
electrons to achieve a stable configuration is known as valency.
This
new concept is based on electronic configuration of an atom and explains
variable valency
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