12th Class Chemistry Chapter 1 Periodic Classification of Elements and Periodicity Short Questions Preparation

Question # 1

What improvements were made in Mendeleev's periodic table.

Ans 1: Mendeleev's periodic law:-Mendeleev's arranged the elements in ascending order of their atomic masses and found that elements with similar properties appeared at regular intervals.
Ans 2: Improvements made in Mendeleev's periodic table: After the discovery of atomic numbers by Moseley in 1911,it was noticed that elements could be classified more satisfactorily by using their atomic numbers,rather than their atomic masses.Hence,the periodic table was improved by arranging the elements in ascending order of their atomic number instead of their atomic masses.This improvement rectified a number of confusions present in the old periodic table.

Question # 2

What is Dobereiner's Law of triads?

Ans 1: Dobereiner a German chemist in 1829,arranged elements in groups called Triads,as each contained three elements with similar properties.

Question # 3

Why the ionization energies decreases down the groups?

Ans 1: Going down in the group,the nuclear charge increases but as the size of the atom and the number of electrons causing the shielding effect also increases therefore ionization energy decreases from top to bottom.

Question # 4

Describe 7^thperiod of modern periodic table.

Ans 1: This period is incomplete.This contains only two normal elements Fr and Ra,ten transition elements and fourteen inner transition elements.The inner transition elements of this period are called Actinides,as they starts after Ac(Actinium).The actinides are also shown at the bottom of the periodic table under the Lanthanides. Due to their scarcity,the inner transition elements are also called Rare Earth Elements.

Question # 5

How do member of group V!-A(except oxygen) show+4 and +6 oxidation state?

Ans 1: Elements of group VI-Aexcept oxygen show covalency of +2,+4 and +6,+2 oxidation shown due to 2 unpaired electrons in the p orbitals.+4 oxidation state is shown when 1 electron from p-orbital is promoted to the next vacant d-orbital,while +6 oxidation state is shown when another electron from s-orbital is also promoted to the next vacant d-orbital.

Question # 6

Why 1^stelectron affinity is negative and 2^ndis positive?

Ans 1: Energy is usually released when electronegative elements absord the first electron and E.A in such case is expressed in negative figure,as in the case of halogens,when a second electron is added to a uni negative ion,the incoming electrons is repelled by the already present negative charge and energy in this process is represented by +ve sign
Ans 2: O+e^------->O^- E.A₁=-141 kj mol^-1O^-+e^-------->O^-2 E.A₂=+780 kj mol^-1

Question # 7

The oxidation state vary in a period,but remain almost constant in a group.Give reason.

Ans 1: The number of electrons in outermost shells goes on changing in periods from left to the right,So oxidation states go on changing.The number of electrons in the outermost shells remains the same in a group,so the oxidation states remains the same.Anyhow,the process of unpairing of electrons may happen in a group and oxidation states may change.

Question # 8

How this confusion is removed in the Modem Periodic Table?

Ans 1: Removal of confusion:Zn,Cd,Hg were placed in a single vertical group,while according to their properties they belonged to two different categories.The same was true for so many other elements placed in the same vertical group in two types of vertical groups,A and B.In modern periodic table,Be,Mg,Ca,Sr and Ba are placed in group IIAand Zn,Cd,Hg in group IIB.

Question # 9

Electrical conductance of metals in group IA generally increases from top to bottom.Explain

Ans 1: The property in mainly due to the presence of relatively loose electrons in the outermost shell of the elements and ease of their movement in the solid lattice.In group IA,generally electrical conductance increases from top to bottom because from top to bottom loosely held electrons are more easily available.

Question # 10

Why melting and boiling points of elements belonging to groups VA-VIIA are lower?

Ans 1: Melting and boiling points of elements belonging to groups VA-VIIA are lower because elements of these groups exist as small,covalent molecules,rather than as three dimensional lattice having very weak intermolecular forces between them.Consequently,their melting and boiling points are extremely low.

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12th Class Chemistry Chapter 1 Periodic Classification of Elements and Periodicity Short Questions Preparation

Online Short Questions For Chapter 1 "12th Class Chemistry Chapter 1 Short Questions Preparation "

Chemistry - 12th Class Chemistry Chapter 1 Short Questions Preparation

What improvements were made in Mendeleev's periodic table.

What is Dobereiner's Law of triads?

Why the ionization energies decreases down the groups?

Describe 7th period of modern periodic table.

How do member of group V!-A(except oxygen) show+4 and +6 oxidation state?

Why 1stelectron affinity is negative and 2ndis positive?

The oxidation state vary in a period,but remain almost constant in a group.Give reason.

How this confusion is removed in the Modem Periodic Table?

Electrical conductance of metals in group IA generally increases from top to bottom.Explain

Why melting and boiling points of elements belonging to groups VA-VIIA are lower?

Prepare Complete Set Wise Questions For Chapter 1 "12th Class Chemistry Chapter 1 Short Questions Preparation "

Set 1

Set 2

Set 3

12th Class Chemistry Chapter 1 Short Questions Preparation - Set 1

What improvements were made in Mendeleev's periodic table.

What is Dobereiner's Law of triads?

Why the ionization energies decreases down the groups?

Describe 7th period of modern periodic table.

How do member of group V!-A(except oxygen) show+4 and +6 oxidation state?

Why 1stelectron affinity is negative and 2ndis positive?

The oxidation state vary in a period,but remain almost constant in a group.Give reason.

How this confusion is removed in the Modem Periodic Table?

Electrical conductance of metals in group IA generally increases from top to bottom.Explain

Why melting and boiling points of elements belonging to groups VA-VIIA are lower?

12th Class Chemistry Chapter 1 Short Questions Preparation - Set 2

Define electron affinity.Give its trend in periodic table.

Melting points of Group VIIA elements increases down the group.Why?

Ionization energy of Al3+ is greater than Mg2+.Give the reason.

Electrical conductance of metals in group IA generally increases from top to bottom.Explain

How do member of group V!-A(except oxygen) show+4 and +6 oxidation state?

Why the second value of electron affinity of an element is usually shown with a positive sign?

The ionic radius of positive ion is smaller than its parent atom.Give reason.

Write a note on blocks in periodic table.

Why melting and boiling points of elements belonging to groups VA-VIIA are lower?

What improvements were made in Mendeleev's periodic table.

12th Class Chemistry Chapter 1 Short Questions Preparation - Set 3

Write a note on blocks in periodic table.

d and f block elements are called transition elements.Give reasons.

The oxidation state vary in a period,but remain almost constant in a group.Give reason.

Lonic radii of negative ion is always bigger in size than its parent atom.Why?

Why melting and boiling points of elements belonging to groups VA-VIIA are lower?

Why the metals are good conductors?

Define electron affinity.Give its trend in periodic table.

Why the ionization energies decreases down the groups?

What is Newland's law of octaves?

M.P and B.P of short periods increase up to middle of period and then decreases.Why?

12th Class Chemistry Chapter 1 Preparation

Describe 7^thperiod of modern periodic table.

Why 1^stelectron affinity is negative and 2^ndis positive?

Describe 7^thperiod of modern periodic table.

Why 1^stelectron affinity is negative and 2^ndis positive?

Ionization energy of Al³⁺is greater than Mg²⁺.Give the reason.