This post explains the answers of questions of worksheet 6 including explanation, diagrams. These solutions will help you complete your assignments and TMA also.
NIOS
Class 10 Science (212) Worksheet 6 Solutions
Q1.
There are numerous elements in nature. Could you
remember location of each element? If yes, how? If not, give reasons why so we
need to classify these elements?
Answer
No,
it is not possible to remember the location and properties of each element
individually.
Reasons
1. There
are over 118 elements know today so far.
2. Each element has specific chemical and
physical properties.
3. Elements
are scattered in nature.
Need
for classification
1. Elements
with similar properties can be arranged into groups.
2. We can easily predict properties of element by knowing its position in the table.
3. We
can understand the relationship of different elements in terms of reactivity,
valency etc.
So, classification of elements is essential
for systematic and scientific study.
Q2.
Name the scientists who first attempted to classify
the elements found in nature. How many attempts have been taken before modern
periodic table is formed?
Answer
Dobereiner
, Newlands and Mendeleev attempted first to classify elements.
Several
attempts including three major attempts were made to classify elements before
the Modern Periodic Table. The modern periodic table was developed by Henry
Mosely.
Q3.
“Mendeleev included noble gas elements in his
periodic table”. Justify this statement.
Answer
Actually,
Mendeleev did not include noble gases in his periodic table because they were
not discovered at that time.
When
noble gases were discovered, they were placed in new group 0 without disturbing
the table.
Mendeleev
left gaps in the table for undiscovered elements so that the new elements could
be placed in the table.
So, we can say noble gases were placed in the
Mendeleev’s periodic table.
Q4.
If a new element is discovered, using your
knowledge of chemistry, explain how you would decide whether it belonged in
group 2, group 4 or group 0 of the periodic table.
Answer
We
know in the Modern Periodic Table, elements are placed into groups based on the
number of electrons in their outermost shell or valence shell.
We can decide to place an element in group:
1. Find
the atomic number on the basis of number of protons or number of electrons.
2. Arrange
the electrons in shells (K, L, M,…) according to 2n2 rule.
3. The number of valence electrons (electrons in outermost shell) determines the group.
(a) if element has two electrons in its outermost shell, it belongs to group 2.
(b) If element has four electrons in its outermost shell, it belongs to group 4.
(c) If element has completely filled outermost shell, it belongs to group 0 (Nobel gases)
In
the last we can also compare the chemical properties of these elements.
Q5.
Why is it important to arrange the elements in the
table rather than a list of elements in the periodic table?
Answer
It
is important to arrange the elements in the form of a periodic table because:
1. Elements
with similar properties can be grouped together in vertical columns or groups.
2. Properties
of undiscovered elements can be predicted easily.
3. Periodicity
in physical properties like atomic size, metallic character, ionization energy
can easily be observed in periods and groups.
4. Elements
can be grouped by properties and electronic configuration so study of these
elements would be easy.
5. Chemical
behaviour can easily be explained.
Q6.
2 isotopes of Nitrogen are N14 and N 15. How would
you place both isotopes in one group or in different group. Give reason in
support of your answer.
Answer
Elements
are arranged on the basis of increasing atomic number in the Modern Periodic
Table.
N-14
and N-15 are isotopes of Nitrogen.
Isotopes
of an element have the same atomic number so these isotopes of nitrogen have
same atomic number (7) and same electronic configuration 1s2 2s2
2p3.
So
both isotopes will be placed in the same group 15 in the modern periodic table.
Q7.
“Modern Periodic Table is superior to Mendeleev
Periodic Table”. Whether you support this or not. Justify this statement.
Yes, I support this statement that the Modern Periodic Table is superior to Mendeleev’s Periodic Table.
Elements were arranged on the basis of atomic mass
in Mendeleev’s periodic table and on the basis of atomic number in Modern
periodic table.
Reasons
why Modern Periodic Table is superior to Mendeleev’s periodic table.
1. Mendeleev
could not place isotopes correctly but due to same atomic number, they were
placed in the same position in the modern periodic table.
2. Some
elements (co & Ni) were placed wrongly
in Mendeleev’s table but they were placed on the basis of increasing atomic number
in the modern periodic table.
3. Groups
and sub groups were not distinguished in Mendeleev’s table but modern periodic
table has clear groups and periods.
4. Properties
of undiscovered elements can be predicted with more precision in the modern
periodic table than Mendeleev ‘s table.
So,
the modern periodic table provides more scientific and accurate arrangement of
elements.
Q8.
Arrange the following elements in increasing order
of their atomic number - Cs, Li, Na, K, Fr, Rb.
Answer
Atomic
numbers of given elements:
Li
= 3
Na
= 11
K
= 19
Rb=
37
Cs
= 55
Fr
= 87
Increasing
order of atomic number
Li(3)
<Na(11)< K(19)< Rb(37)< Cs(55)< Fr(87)
Q9.
“The importance of atomic number as the fundamental
property was realized by Henry Mosely”. Give reasons in support of this
statement.
Answer
Henery
Moseley found many defects in the Mendeleev’s periodic table in which elements
were arranged on the basis of atomic mass.
Henry
Moseley discovered that the atomic number is the fundamental property of an
element. Atomic number of an element is the number of protons in the nucleus of
its atom. Since an atom is neutral so the number of electrons is equal to the
number of protons.
So
each element has unique atomic number.
1. Each element has its specific position in the
periodic table on the basis of increasing order of atomic number.
2. Incorrect
placements of some elements (Co & Ni) were resolved.
3. Isotopes
of an element placed at the same position.
Q10.
The elements of a period are given below is order
from left to right with missing of 2 elements.
Na, Mg, Al, P, S, Cl
Answer the following questions:
a. Name the period which these elements belong to.
b. Name all these two missing elements.
c. Make correct arrangement of the elements as answer the question
“a” and question “b”.
d. Identify these elements as metal, non-metal and noble gas.
Answer
(a) Elements belong to period 3rd .
(b) Two missing elements are Silicon (Si) and Argon (Ar).
(c) Arrangement of elements in third period – Na , Mg, Al , Si , P , S, Cl , Ar
(d) Classification of elements:
Metals - Na , Mg , Al
Metalloids - Si
Non-
metals - P, S, Cl
Noble gases - Ar
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