1. Define valency and describe its variation in a
period and a group.
Ans: Valency of an element is its combining capacity.Valency of an element = number of valence electrons (if equal to or less than 4)Valency of an element = 8 — number of valence electrons (if more than 4)
2. What happens to the metallic character of
the elements as we move in a period from left to right in the periodic table?
Give reason.
Ans: Metallic character of the element decreases along a period due to decrease in atomic size along a period or outermost electrons are closer to nucleus. So they cannot be easily lost.
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?
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?
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. He predicted that 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.
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.
Check your understanding:
1) What is the atomic radius of an atom?
2) What is the trend in atomic radius across a
period?
3) The trend in atomic radius across a period
is caused by _____.
4) What generally happens to atomic radii as
one goes down a group or a family?
5) Write the equation for the ionization of an
atom.
6) Why
inert gases have zero valency?
7) What is ionization energy?
8) Which group or family has the lowest
ionization energy?
9) Group 18 or 8A, the noble gases, have the
highest ionization energy (True or False).
10) Elements with a high ionization energy lose
electrons easily (True or False).
11) The increase in ionization energy across a
period is caused by _____.
12) Why does ionization energy generally
decrease going down a group or family?
13) What is meant by electron shielding?
14) What is the second ionization energy of an
atom?
15) What is electron affinity?
16) Write the equation for electron affinity
for an exothermic process.
17) Write the equation for electron affinity
for an endothermic process.
18) Which group or family gains electrons most
easily?
19) Name two elements, other
than Gallium, whose existence was predicted by Mendeleev
20) How does
the electrronegetive character of elements vary along a period of the periodic table?
Periodic
Properties of Elements in modern periodic tables Class X (10th)
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10th Periodic Classification Notes
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Periodic Classifications Solved Questions Paper
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Periodic classification of elements question bank
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