Saturday, 17 February 2018

2nd Year Chemistry Chapter 1 Important Short Questions

2nd Year Chemistry Chapter 1 Important Short Questions
Here we have written Important short questions of chapter 1 Periodic Classification of Elements and Periodicity 2nd-year chemistry

Chapter 01

Ql Lanthanide contraction controls the atomic size of the elements of the 6th and the 7t
Ans: Lanthanides are present in the 6th period and actinides are the members of 7th
periods. In case of Lanthanides and actinides, the valence electrons are entering the 4f &
5f orbitals respectively where they experience more nuclear pull due to increased effective
nuclear charge which causes the decrease in atomic size (lanthanide contraction). That is why
the atomic sizes of lanthanides and actinides and actinides are affected by the lanthanide
Q2 Explain why ‘D’ and ‘F’ blocks are called transition elements?
Ans: d-block and f-bock elements are present in between the s & p block elements in the
modern Periodic Table. Their properties are in between the s & p-block elements varying
from left to right. It means that their properties show a systematic transitional phase from
metallic & non-metallic behavior, therefore, they are called transition elements.
Q3 Oxidation states vary in a period but remain almost constant in the group?
Ans: Oxidation state depends upon no unpaired of electrons present in the valence shell.
Since the no of electrons present in the valance shell remain same in the group so oxidation
the state remains same down the group on moving from left to right the number of electrons
vaiƧy so the oxidation state of an atom also change across the period.
Q4: The hydration energies of ions are in the following order Al+3 > Mg+2 > Na+1
Ans: Hydration energies depends upon the charge density of ions i.e Greater the charge
density more will be the hydration energy. Charge to size (charge density) is maximum for
the Al3 and minimum for the Na’. Therefore the hydration energies are in the order.
Al+3 > Mg+2 > Na+1
Q5 Alkali metals give ionic hydrides?
Ans: Hydrides are the binary compounds of Hydrogen. Their nature depends upon the
type of bonding present in them. Since alkali metals are much more electropositive than the
hydrogen so the lose the electron and give it to hydrogen forming the positive ion and
hydrogen the negative ion. Since the bond is formed between metal and hydrogen due to
the transfer of electron hence ionic hydrides are formed.
Q6 Although both sodium and phosphorus are present in the same period of the periodic
table yet their oxides are dEferent in nature NkO is the basic and P205 is acidic in nature?
Ans: The nature of oxides depends upon the nature of element forming oxides. When
moving from left to right there is the change in metallic character from left to right te at the
left metal at the right nonmetals.
Metals from basic oxides and nonmetals from acidic oxide that is why both sodium and
phosphorus are present in the same period of the periodic table yet their oxides are
different in nature Sodium being metal forming the basic oxides Na20 and Phosphorus
being nonmetal forming acidic oxides P205.
Q7: Ionic character of halides decreases from left to right in a period?
Ans: Ionic character of halides depends upon the difference of electronegativity of bonded
atoms. M we remove from left to right across the period the electronegativity of element
increase and the difference with respect to halogen decrease hence the ionic character of
halides decrease across the period.
Q8: Why the oxidation state of noble gases is usually zero?
Ans: noble gases have completely filled s & p orbital of their valance shell Due to this
stable electronic configuration they cannot gain or lose the electron hence they show
usually zero oxidation state. Eg He, Ne, Ar, Kr, Xe
Q9: Why diamond is a non-conductor and graphite is a good conductor?
Ans: In case of diamond, all the four valence electrons of carbon are tetrahedral bonded
with the neighboring hence not free electrons are available for conduction so it is the poor
the conductor of electricity whereas in case of graphite one electron is free along the layer of
an atom which carries the current hence graphite is a good conductor.
Q10: Describe essential features of period number six of the periodic table?
And: It is the longest period of periodic table having 32 elements. In this period there are
eight representative elements, ten transition elements and fourteen elements of Actinides
starting from 89Ac.
Q11: Why the alkali metals are the strong reducing agent?
Ans: Because they have lower ionization energies, alkali metals readily lose the valance
electron hence they act as the reducing agent.
Ql2: Why hydrogen can be placed at top of group IA,4A, & 7A of the periodic table?
Am: In the periodic table elements are placed according to theft electronic configuration
into groups and periods. Hydrogen possess one electron in the outer most shell like alkali
metals, Hydrogen possess half-filled valance shell like 4A group and needs one electron
complete its outer most shell like halogens so it can be placed at the top of group l-A, 4-A
& 7-A of the periodic table.
Q13: Define group and period. How many elements are there in period number I?
Ans: Verticacolumnnm in the periodic table are called groups whereas the horizontal rows
are called the periods. There are seven periods and eight groups in the periodic table. Two elements Hydrogen and Helium are present in the first period.
Q14 Define Lanthanide contraction?
Ans: The gradual decrease in atomic and ionic radii with increasing atomic number
among the lanthanides elements with atomic number from 51 to 71 lanthanide
contraction. The decrease arises because of a gradual increase in effective nuclear charge
through the lanthanides series.
Ql5: State modem Periodic Law?
Ans: Physical and chemical properties of elements are the periodic function or theft
atomic numbers.
Q16: What are covalent halides ? Give two examples.
Ans: The binary compounds of halogen formed by sharing the electrons are called
covalent halides. Examples are SiCI4, PCI3 & S2Cl2.

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