Solved Questions Set-01
Q.1. Why does silicon is classified as
Metalloid?
Ans:
Silicon is gray color solid at room temperature with very
high melting point and boiling point that lose or gain 4
electrons [ 3s2, 3p2] having both metallic and non metallic properties
so it is classified as Metalloid eg. Sio2
Q.2.Why inert gases have zero valencies?
Ans: It is because Inert
gases have 2 or 8 electrons in valence shell.
Q.3. How is valency of an element
determined?
Ans: The valency of an
element measures its ability to combine with other elements. The valency is
determined by knowing place in periodic table.. All the elements in group VIII
have eight electrons in their outer shells, and thus have a valency of zero
(highly stable). Elements in group I just have one valence electron in their
outer shells and thus have a valency of one.
Q.4. why could no fixed position be given
to hydrogen in Mendeleev’s Periodic table?
Ans: Hydrogen placed in the
first column above alkali metals. it is because hydrogen
and alkali metals have similar properties.
However, hydrogen also
resembles halogens. Like halogens, hydrogen is a gas, and exists as a diatomic
molecule (H2). It forms covalent compounds like halogens
unlike alkali metals. Hence, it can also be placed above the halogen
group .Therefore, Mendeleev was not able to explain
the position of hydrogen.
Q.5. In modern periodic table, the
isotopes of Chlorine Cl-35 and Cl-37 having different atomic masses will
be
kept in different slots or they would be assigned same position on
the basis of their chemical properties? Give reason in support of your
answer
Ans: It is
because periodic table is based on the atomic numbers of the
element and both the isotopes of chlorine have the same atomic number
(Z = 17).
Q.6. Why was Dobereiner’s system of
classification of elements into triads not found to be useful?
Ans: it is because he could
not arrange all elements in triads.
Q.7. Oxygen (O, 8) and sulphur (S, 16)
belong to group 16 of the periodic table :-
(i) Write the electronic configuration
and valency of these two elements?
(ii) Which among these will be more
electronegative? Why?
Ans: (i) Oxygen (O, 8) = 2,6
; Vacancy =2
Sulphur (S, 16) = 2,8,6
; Vacancy =2
(ii) Oxygen will be
more electronegative due to electro negativity decreases from top to bottom
because atomic size increases.
Q.8. How does electronic configuration of
atoms change in a period with increase in atomic number?
Ans. On moving across
a period from left to right, the atomic number of the elements increases,
therefore, the number of electrons in the valence shell increases from 1 to 8,
i.e, the first element in the given period will have one electron in its
valence shell and the last element in the same period will have eight electrons.
Q.9. What happens to the melting points
and boiling points of elements while moving down in a group?
Ans. The melting
points and boiling points decrease while moving down in group of metals.
The melting points and
boiling points increases while moving down in group of non-metals.
Q10. Why Chlorine (atomic number 17) is
more electronegative than sulphur (atomic number 16)
Ans: The nucleus of
chlorine has more tendency to attract an extra electron than the nucleus of
sulphur because chlorine needs only one 1 electron to complete its shell.
Hence, chlorine is more electronegative than sulphur.
Solved
Questions Set-02
1. How does the electronic configuration
of an atom relate to its position in the Modern periodic table?
Ans. The outermost electron in electronic
configuration give idea of group in Modern periodic table and also period.
2.
Give examples of some : a. Metalloids b. Alkali metals c. Halogens d.
Alkaline Earth metals e. Nobel gases or inert elements
Ans:
a. Metalloids – Boron, Silicon, Germanium
b.
Alkali metals – Sodium, lithium, Potassium
c.
Halogens – Fluorine, Chlorine, Bromine
d.
Alkaline Earth metals – Magnesium, Calcium
e.
Nobel gases or inert elements – Helium, Neon, Krypton
3. How were the positions of different
isotopes decided in modern periodic table?
Ans: All the isotopes of an element
have same atomic numbers. In modern periodic table, the elements have been
allotted places based on their atomic numbers. Therefore, all the isotopes of
an element have been assigned the same position in the modern periodic table
4. Where do you think hydrogen
should be placed in the modern periodic table?
Ans: The modern periodic table is based
on the atomic numbers of the elements and also upon their electronic
distribution. Alkali metals as well as hydrogen have one electron in their
valence shell. Therefore, hydrogen should be placed in the group of alkali
metals. However, it has been assigned a separate position and is not a member
of the group of alkali metals since it is a non-metal.
5. How were the positions of the elements
Co and Ni resolved in the modern periodic table?
Ans: On the basis of atomic masses, Ni
(58.7) should be placed before Co (58.9). This was defect in Mendeleev’s table
because the element Co was placed before Ni. However, the atomic number of (Co
= 27) is less than that of Ni ( 28). Therefore, they have been correctly
arranged in the modern periodic table.
6. The two isotopes of chlorine have
atomic masses 35 u and 37 u. Should they be placed in same slot in the periodic
table?
Ans: Yes, they should be placed in the
same slot because periodic table is based on the atomic numbers of the element
and both the isotopes of chlorine have the same atomic number (Z = 17).
7. Which element is bigger in
size, lithium (Z = 3) or Sodium (Z = 11) and why?
Ans: Lithium (Li) atom has only
two shells K and L in it whereas a sodium (Na) atom has three shells K L and M.
Since a sodium atom has one mote shell than a lithium atom, therefore
sodium atom is bigger in size.
8. What were the criteria used by
Mendeleev in creating his periodic table?
Ans: Ans. Mendeleev’s periodic table
was based on the observation that properties of the elements are a periodic
function of their atomic masses. This means that if elements are arranged in
the increasing order of their atomic masses, then elements with similar
properties get their place in the same group in a successive increasing order
of atomic masses.
9. Why did Mendeleev leave some gaps in
his periodic table?
Ans. Mendeleev left gaps in his periodic
table to keep the elements with similar properties together if predicted. New
elements would be discovered later and they would occupy those gaps.
10. Why did Mendeleev treated the
hydrides and oxides of element as the basic properties of
elements for their classification?
Ans. During the period when Mendeleev
gave his periodic table atomic numbers and electronic configurations were not
known. Comparison of properties of elements could be best done by comparing
their compounds. He selected oxides and hydrides because oxygen and hydrogen
form compounds with most of the elements due to their high reactivity.
11. Why are the elements in the same
group of the periodic table show close resemblance in their chemical behavior?
Ans: The chemical
properties depend upon the number of valence electrons of an
element. The elements in the same group of the periodic table show close
resemblance in their chemical behavior as they have same number of valence
electrons.
12. What happens to atomic radii in
a group and period and why?
Ans: Atomic radius is the
distance between the centre of atom and the outermost shell.
In a period, atomic radius generally
decreases from left to right.
In a period there is a gradual increase
in the nuclear charge. Since valence electrons are added in the same shell,
they are more and more strongly attracted towards nucleus. This gradually
decreases atomic radii.
Atomic radii increase in a group from top
to bottom.
As we go down a group the number of
shells increases and valence electrons are present in higher shell and
the distance of valence electrons from nucleus increases. Also, the
number of filled shells between valence electrons and nucleus increases
Both the factors decrease the force of attraction between nucleus and valence
electron. Therefore, atomic size increases on moving down a group.
13. Why are the ionization
energy of elements increases in a period from left to right.
Ans: The minimum amount of energy
required to remove an electron from a gaseous atom in its ground
state to form a gaseous ion is called ionization energy.
The ionization energy increases
in a period from left to right. This is because the force of attraction between
valence electron and nucleus increases in a period from left to right.
14. What do you mean by Electron
affinity: How it is vary in group and periods in modern periodic table?
Ans: The tendency of element to gain an
additional electron. This ability is measured by electron affinity. It is the
energy change when an electron is accepted by an atom in
the gaseous state. Electron affinity is assigned a positive value
when energy is released during the process. Greater the value of electron
affinity, more energy is released during the process and greater is the
tendency of the atom to gain electron.
In a group, the electron affinity
decreases on moving from top to bottom as less and less amount of
energy is released.
In a period, the electron affinity
increases from left to right, as more and more amount of energy is released
15. What do you mean by Electro
negativity?
Ans: Electro negativity is relative
tendency of a bonded atom to attract the bond-electrons towards itself. It just
compares the tendency of various elements to attract the bond-electrons towards
themselves.
Electro negativity decreases in
a group from top to bottom. Electro negativity increases in a period from left
to right. Electro negativity is related to ionization energy. Electrons
with low ionization energies have low electro negativity because their nuclei
do not exert a strong attractive force on electrons. Elements with high
ionization energies have high electro negativity due to the strong pull exerted
on electrons by the nucleus.
Solved Questions Set-03
VERY SHORT ANSWER TYPE QUESTION (1 MARKS)
1. In the modern periodic table which are
the metals among the first ten elements.
Ans. Only lithium, beryllium.
2. By considering their position in the
periodic table which one of the following elements would you expect to have
maximum metallic characteristic? Ga, Ge, As, Se, Be.
Ans. Ga.
3. Which of the following statement is
not correct statement about the trends when going from left to right across the
periods of periodic table.
A. The element becomes less metallic in
nature.
B. The number of valence electron increase.
C. The atoms lose their electron more
easily
D. The oxide becomes more acidic
Ans. The atoms lose their electron more
easily.
4. Element X forms a chloride with the
formula XCl2 which is solid with a high melting point. X would most likely be
in the same group of periodic table as (a). Na (b). Mg (c). Al (d). Si?
Ans. (b). Mg
5. Which element has two shells, both of
which are completely filled with electrons?
Ans. Ne (2,8).
6. The electronic configuration 2, 8, 2 ?
Ans. Mg (2,8,2).
7. A total of three shells, with four
electrons in its valence shell?
Ans. Si (2,8,4).
8. A total of three shells, with three
electron in its valence shell?
Ans. Al(2,8,3).
9. Twice as many electrons in its second
shell as in its first shell?
Ans. C (2,4).
10. Nitrogen(atomic number=7) and
phosphorus(atomic number=15) belong to same group-15 of the periodic table.
Write the electronic configuration of these two elements. Which of these two
will be more electronegative? Why.
Ans. Electronic configuration of N (7) =
2, 5 Electronic configuration of P (15) = 2, 8,5
Nitrogen will be more
electronegative due to electro negativity decreases from top to bottom because
atomic size increases.
11. In the modern periodic table Ca (At
no. = 20) is surrounded by elements with atomic number 12, 19, 21, and 38.
Which of these have physical and chemical properties resembling Ca.
Ans. 38,12
VERY SHORT ANSWER TYPE QUESTION (2-marks each)
Q.1. Did Doberenier‘s triads also exist
in the column of Newland octaves. Compare and find out.
Ans. Yes, Li, Na, K
Q.2. What are the limitation of
Dobernier‘s classification?
Ans. Only few elements are classified
into triads. So, this classification is rejected.
Q.3. What are the limitations of Newlands
law of Octaves
Ans. (a) It was applicable only upto
atomic mass 40 of Ca. (b) Two elements Ni and Co are placed in
column as F, Cl, Br which have different properties.
Q.4. Use Mendeleev‘s periodic table to
predict the formula for the oxide of following element K, C, Ba, Al
Ans. K –I A –K2O C -IV A –CO2 Al –III
A-Al2O3 Ba –II A –BaO
Q.5.Besides Ga, which other elements have
been discovered that were left by Mendeleev in his periodic table (Any two)?
Ans. Eka-Boron-Scandium
Eka-Silicon-Germanium
Q.6. What were the criteria used by
Mendeleev in creating his periodic table?
Ans. Two criteria used by Mendeleev (i)
Atomic mass (ii) Similar chemical properties
Q.7. Why do you think the noble gases are
placed in a separate group?
Ans. These gases were discovered
very late and placed in a separate group because they were inert.
Q.8. Name two elements you would expect
to show chemical reaction, similar to magnesium. What is the basis for your
choice?
Ans. Ca, Be On the basis of the elements
belong to same group-2. So valance electrons are same.
Q.9. (a) What property do all elements in
the same column of the periodic table as Boron have in common
b) What property do all elements in the
same column of the periodic table as Fluorine have in common?
Ans. (a) All elements in the same column
as Boron have 3e- in valence shell and form oxide X2O3.
(b) All elements in the same column as
Fluorine have 7e- in valence shell so their valency is one.
Q.10. An atom has electronic
configuration 2,8,7 (a) What is the atomic no. of this
element? (b) To which of the following elements
would it be chemically similar N(7) F(9) P(15) Ar(18)
Ans. (a) Atomic no=17 (b) F(9).
Short answer type question (3-marks each)
Q.1-How could the modern periodic table
remove various anomalies of Mendeleev’s periodic table?
Ans-Various anomalies are removed in
following ways-
(a) The position for all isotopes of an
element justified since they have same atomic number.
(b) The position of certain elements
which are earlier misfit like Co-58.9 is placed before Ni-58.7 are now justified because Co has lower atomic number than Ni.
(c) Cause of periodicity explained due to
same electronic configuration repeated after certain gap.
Q.2- Name
(a) three elements that have a single
electron in their outermost shells.
(b) two elements that have two electrons
in their outermost shells.
(c) three elements with filled outermost
shell.
Ans- (a) Li ,Na ,K(Group-1)
(b Be ,Mg
(Group-2)
(3) Ne ,Ar, Kr (Group-18)
Q.3- (a) Li,Na,K are all metals that
react with water to liberate H2 gas .Is there any similarity in the atoms of
these elements.
(b) Helium is an unreactive gas and Neon
gas is a gas of extremely low reactivity, what do their atoms have in common.
Ans-(a) there are following similarities.
(1) these atoms have same number of electrons
in outermost shell 3Li -2,1 11Na-2,8,1 19K-2,8,8,1
(2) Li,Na,K react with oxygen to form
oxide which are basic in nature.
(b) both He and Ne have completely filled
shell
Q.4-The position of three elements A,B
and C in the periodic table are shown below
Group-16
|
Group-17
|
-
|
-
|
-
|
A
|
-
|
-
|
B
|
C
|
(a) State whether A is a metal or
non-metals.
(b) State
whether C is more reactive or less reactive than A.
(c) Will C be larger or smaller in size
then B.
(d) Which type of ion, cat ion or
anion will be formed by element A
Ans-(a)-Non-metal
(b) A is more reactive due to small size,
have more tendency to accept outside electron
(c) C is smaller in size than B due to
atomic size decreases from left to right in a period
(d) Anion formed due to tendency to
accept electron
Q5. How are the positions of elements related to their atomic
number in the Modern periodic table?
Ans.
The number of valence electrons present in an atom of an element is equivalent
to the group number, while the total number of shells give the period
number in which the element to present.
e.g.
1. Atomic no. of Mg=12 ; Electronic
configuration=2,8,2 therefore, Group. no.=2 or
IIA Period no.=3 e.g.
2. Atomic no. of Cl=17; Electronic
Configuration=2,8,7 therefore, Groupp.
no.=17th or VIIA
Solved Questions Set-04
Q1.
What is Modern periodic Law?
Ans.
The Properties of elements are a periodic function of their atomic number.
Q2.
What were the limitations of Dobereiner Law of triads?
Ans.
Dobereiner could identify only 3 triads from the element known at that time.
Hence, this system is not useful.
Q3.
State Newlands’s law of Octaves.
Ans.
Newland arranged the elements in the increasing order of the atomic masses and
found that every eight element had properties similar to that of the first like
the notes of music.
Q4.
What were the limitations of Newlands’s Law of Octaves?
Ans.
1. It was only applicable only up to Calcium as after Calcium every eighth
element did not posses , properties similar to that of first.
2. At
a few places unlike elements were put together like cobalt and nickel along
with F, Cl and Br.
Q5.
Which 2 criteria did Mendeleev used to classify elements in his periodic table?
Ans.
Atomic mass and similarity in chemical property.
Q6.
State Mendeleev’s periodic law.
Ans.
Properties of elements are a periodic function of their atomic masses.
Q7.
Why did Mendeleev leave gap in his periodic table?
Ans.
Mendeleev place elements with similar properties one below the other leaving
gap for yet undiscovered elements.
Q8.
Name the elements which have since been discovered that were left by Mendeleev
in his Periodic Table?
Ans.
Eka Boron – Scandium
Eka
Al - Gallium Eka Si
- Germanium
Q9.
What are the limitations of Mendeleev's periodic table?
Ans.
1. Position
of Isotopes was not clear in his table.
2.
Wrong Order of atomic mass of certain elements – Elements with higher
atomic mass were placed before elements having lower atomic mass.
e.g. Cobalt was placed before nickel.
3.
Position of hydrogen was not clear in his periodic table.
Q10.
How were the drawbacks of Mendeleev's periodic table resolved in the modern periodic table?
Ans.
As the modern periodic table was based on the atomic numbers so all the
isotopes could be placed together in one slot. Secondly,
the wrong order of atomic masses was also sorted as Cobalt's atomic number was lower than Nickel even though it had a
higher atomic mass.
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