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

Question # 1

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

Ans 1: By moving from left to right in a period,the outer shell remains the same,while the nuclear charge increases effectively that makes the removal of an electron difficult and hence the value of ionization energy increases.Similarly the size of Al is smaller than Mg so Al³⁺it has greater ionization energy than Mg²⁺.

Question # 2

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

Ans 1: For elements of group VIIA,which exist in the form of molecules,the melting and boiling points increase down the group.This is because large molecules exert stronger force of attraction due to their higher polarizabilities.

Question # 3

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 # 4

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

Ans 1: The removal of electrons causes an imbalance in proton-electron ratio.Due to greater attraction of the nuclear charge,the remaining electrons of the ion are drawn closer to the nucleus.thus,a positive ion is always smaller than the neutral atom from which it is derived.The radius of Na is 157 pm and the radius of Na is 95 pm.

Question # 5

Give two defect of Mendeleev's periodic table.

Ans 1: Two defect of Mendeleev's periodic table:
Ans 2: i) It does not explain the position of isotopes.
ii) It does not explain the wrong order of atomic masses of elements.

Question # 6

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

Ans 1: Melting and boiling points of short periods: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 groups IA element are low because each atom in them provides only one electron to for a bond with other atom.Melting point of group IIA elements are considerable higher than those of group IA elements because each atom in them provides two binding electrons.

Question # 7

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 # 8

Define Metalloid.

Ans 1: Metalloid: Some elements,especially lower members of groups,IIA,IVA and VA have properties of both metals as well as non-metals.These elements are called metalloids.

Question # 9

Why the metals are good conductors?

Ans 1: Metal are good conductors due to the presence of relatively loose electrons in the outermost shell of the element and ease of their movement in the solid lattice.

Question # 10

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.

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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

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

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

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.

Give two defect of Mendeleev's periodic table.

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

Why 1stelectron affinity is negative and 2ndis positive?

Define Metalloid.

Why the metals are good conductors?

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

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

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

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

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.

Give two defect of Mendeleev's periodic table.

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

Why 1stelectron affinity is negative and 2ndis positive?

Define Metalloid.

Why the metals are good conductors?

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

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

Define Metalloid.

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

What is lanthanide contraction?

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

Why do metals conduct electricity?

Why metallic character increases from top to bottom in a group of metals?

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

How this confusion is removed in the Modem Periodic Table?

Describe 7th period of modern 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.

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

Solution of Na2O in water is alkaline.Justify the statement.

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

How melting and boiling points varied in a period?

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

What improvements were made in Mendeleev's periodic table.

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

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

Give two defect of Mendeleev's periodic table.

12th Class Chemistry Chapter 1 Preparation

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

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

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

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

Describe 7^thperiod of modern periodic table.

Solution of Na₂O in water is alkaline.Justify the statement.