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

Question # 1

What is Newland's law of octaves?

Ans 1: Newland who was English chemist,in 1864,classified 62 elements,known at that time,in increasing order of their atomic masses.He noted that every eight element had some properties in common with the first one.The principle on which this classification is based was called the law of Octaves.

Question # 2

Why the oxidation state of noble gases is usually zero?

Ans 1: Group VIII A elements,which are also called zero group elements usually show zero oxidation state because there is no vacancy in their outer most shell to accommodate more electrons.

Question # 3

Define electron affinity.Give its trend in periodic table.

Ans 1: Electron affinity:Energy released or absorbed,when an electron is added to a gaseous atom to form a negative ion is called electron affinity.
Ans 2: Trend of electron affinity in periodic table:Electron affinity generally increases with increasing atomic number within a period and decreases from lighter to heavier elements in a given group of the periodic table.

Question # 4

How melting and boiling points varied in a period?

Ans 1: Across the short periods,the melting and boiling points of elements increase with the number of valance electrons up to group IVA and then decrease up to the noble gases.The melting points of group IA element are low because each atom in them provides only one electron to for a bond with other atom.Melting points of group IIA elements are considerable higher than those of group IA elements because each atom in them provides two binding electrons.An important change occurs when we move from group IVA to group VA,VIA,VIIA as the lighter elements of these group exist as small covalent molecules.Rather than as three dimensional lattices.

Question # 5

Discuss the trend of inoization energy in periodic table.

Ans 1: Trend of ionization energy in periodic table:In groups ionization energy decrease from top to bottom because size of atom and number of electrons causing the shielding effect also increases.
Ans 2: In period by moving from left to right the outer shell remains the same while the nuclear charge increase effectively that makes the removal of an electron difficult and hence the value of ionization energy increases.

Question # 6

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 # 7

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

Ans 1: Energy 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 added to a uni-negative ion,the incoming electron is repelled by the already present negative charge and energy is absorbed in the process.
Ans 2: O+e^--------->O^-E.A=-141 kj mole^-1
O^-+e^-------->O^-2E.A₂=+780 kj mole^-1

Question # 8

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 # 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

What is lanthanide contraction?

Ans 1: Lanthanide contraction:The atomic number increases from left to right,the atomic radius decreases,This gradual decrease in the radius is due to increase in positive charge in the nucleus.As the positive charge increases,the negatively the outer most shell becomes gradually smaller.This effect is quite remarkable in the elements of longer periods in which d and f subshells are involved.For example the gradual reduction in the size of Lanthanides is significant and called Lanthanide Contraction.

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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 is Newland's law of octaves?

Why the oxidation state of noble gases is usually zero?

Define electron affinity.Give its trend in periodic table.

How melting and boiling points varied in a period?

Discuss the trend of inoization energy in periodic table.

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?

What improvements were made in Mendeleev's periodic table.

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

What is lanthanide contraction?

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 is Newland's law of octaves?

Why the oxidation state of noble gases is usually zero?

Define electron affinity.Give its trend in periodic table.

How melting and boiling points varied in a period?

Discuss the trend of inoization energy in periodic table.

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?

What improvements were made in Mendeleev's periodic table.

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

What is lanthanide contraction?

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

Discuss the trend of inoization energy in periodic table.

What is Dobereiner's Law of triads?

Write a note on blocks in periodic table.

How this confusion is removed in the Modem Periodic Table?

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

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

How the classification of elements in different blocks help in understanding their chemistry?

Define Metalloid.

What improvements were made in Mendeleev's periodic table.

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

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

Discuss the trend of inoization energy in periodic table.

Write a note on blocks in periodic table.

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

Why 1stelectron affinity is negative and 2ndis positive?

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

Why the ionization energies decreases down the groups?

Define Metalloid.

Why the oxidation state of noble gases is usually zero?

How the classification of elements in different blocks help in understanding their chemistry?

What improvements were made in Mendeleev's periodic table.

12th Class Chemistry Chapter 1 Preparation

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