WBBSE Class 10 Physical Science Solutions Chapter 8.1 Periodic Table and Periodicity of the Properties of Elements

Detailed explanations in West Bengal Board Class 10 Physical Science Book Solutions Chapter 8.1 Periodic Table and Periodicity of the Properties of Elements offer valuable context and analysis.

WBBSE Class 10 Physical Science Chapter 8.1 Question Answer – Periodic Table and Periodicity of the Properties of Elements

Very Short Answer Type Questions :

Question 1.
Periodic changes of what occur in a periodic table?
Answer:
Physical and chemical properties of sets of elements arranged in some manner change periodically.

Question 2.
How does atomic size of elements change in a group?
Answer:
Atomic size gradually increases downward in a yroup.

Question 3.
How does electronegativity of elements change along a period of periodic table?
Answer:
Electronegativity of elements gradually increases along a period from left to right of periodic table.

Question 4.
How many groups are there in the long form periodic table ?
Answer:
There are 18 groups in the long form periodic table.

Question 5.
How does metallic character of elements change in a group in periodic table?
Answer:
Metallic character of elements gradually increases downward in a group.

Question 6.
Which is more fundamental-atomic number or atomic weight of elements ?
Answer:
Atomic number is more fundamental than atomic weight of elements.

Question 7.
How are elements arranged in Mendeleev’s modern periodic table?
Answer:
Elements are urianged in Mendeleev’s modern periodic table in ascending order of their atomic number.

Question 8.
What is the position of chlorine in the Mendeleev’s periodic table?
Answer:
The position of chlorine in the Mendeleev’s periodic table:
Period : 3
Group : VIIB

Question 9.
In which group of Mendeleev’s periodic table are kept the alkali metals ?
Answer:
Alkali metals are kept in group IA in Mendeleev’s periodic table.

Question 10.
What is the name ‘Oxygen’ group ?
Answer:
Chalcogens, group.

Question 11.
What are ‘d’-block elements called?
Answer:
‘d’-block elements are called transition elements.

Question 12.
What are ‘f’-block elements called ?
Answer:
‘f’-block elements are called inner transition elements.

Question 13.
How many elements are there in first period of Mendeleev’s periodic table?
Answer:
The first period contains two elements. (Hydrogen and Helium)

Question 14.
What is the name of first group elements of periodic table ?
Answer:
The first group elements of periodic table are called alkali metals.

Question 15.
What is the decreasing order of electron affinity of F, Cl, Br ?
Answer:
The decreasing order of electron affinity of F, Cl, Br is Cl>Br>F.

Question 16.
Is Cobalt a transition element ?
Answer:
Yes, Cobalt is a transition element.

Question 17.
Is the second I.P. is always greater than the first I.P. of a given species?
Answer:
The second I.P. is always greater than the first I.P. of a given species.

Question 18.
Is radioactivity a periodic property ?
Answer:
Radioactivity is not a periodic property.

Question 19.
Between K and C a atom which one has larger in size ?
Answer:
K atom has larger in size than Ca atom.

Question 20.
What is the symbol of the element having atomic number 109 ?
Answer:
The symbol of the element having atomic number 109 is Mt.

Question 21.
Who proposed modern periodic law ?
Answer:
Modern periodic law was proposed by Mosely.

Question 22.
What are representative elements ?
Answer:
Elements of s-and p-blocks are collectively known as normal or representative elements.

Question 23.
What are the elements of second period called ?
Answer:
Elements of second period are called bridge elements.

Question 24.
What are the elements of third period called ?
Answer:
Elements of third period are called typical elements.

Question 25.
Between Na and \(\mathbf{N a} a^{\oplus}\) which one has greater is size ?
Answer:
Na has greater in size than \(\mathbf{N a} a^{\oplus}\).

Question 26.
Between Cl and \(\mathrm{Cl}^{\Theta}\) which one has smaller in size ?
Answer:
Cl has smaller in size than \(\mathrm{Cl}^{\Theta}\).

Question 27.
Between \(\mathbf{N a} a^{\oplus}\) and Mg²⁺ which one has smaller in size ?
Answer:
Mg²⁺ has smaller in size than \(\mathbf{N a} a^{\oplus}\).

Question 28.
Are Van der Waal’s radii larger than covalent radii ?
Answer:
Van der Waal’s radii are larger than covalent radii.

Question 29.
Atomic radii decrease across a period. However, at the end of each period there is increase in atomic radii. Why?
Answer:
Because atomic radii in case of noble gases are Van der Waal’s radii.

Question 30.
Have ionisation energies a positive value?
Answer:
lonisation energies have a positive value.

Question 31.
Why halogens have high values of electron affinity ?
Answer:
Halogens have high values of electron affinity due to their ns² np⁵ configuration.

Question 32.
What is the classification of elements ?
Answer:
The method of arranging similar elements together and separating them from dissimilar elements is called classification of elements.

Question 33.
What is the law of triads?
Answer:
According to law of triads, in a triad of elements, having similar properties, the atomic weight of the central atom was merely the arithmetic mean of the atomic weights of the other two elements.

Question 34.
Between Br and I which one has metallic character ?
Answer:
Between Br and I, iodine has metallic character.

Question 35.
What is the valency of an alkali metal ?
Answer:
The valency of an alkali metal is 1.

Question 36.
What is the relation between N^3- and O^2- ?
Answer:
N^3- and O^2- are iso-electronic ions.

Question 37.
Which halogen is radioactive element?
Answer:
Astatine (At) is the only radioactive halogen.

Question 38.
Which group of elements was missing from Mendeleev’s original periodic table?
Answer:
Mendeleev’s original periodic table did not contain noble or inert gases belonging to Group 18 of the modern periodic table.

Question 39.
In. which period of the periodic table are first transitonal elements found?
Answer:
The first series of transitional elements belong to the 4th period.

Question 40.
X, Y and Z are the elements of a Dobereiner’s triad. If the atomic mass of X be 20 and that of Z be 40, What should be the atomic mass of Y ?
Answer:
Atomic mass of Y = Arithmetic mean of atomic masses of X and Z = \(\frac{20+40}{2}\) = 30

Question 41.
Mention the position of the radioactive alkall metal.
Answer:
Francium (Fr), the radioactive alkali metal, has the position in 1st group of 7 th period.

Question 42.
Name the lanthanide having the lowest atomic number.
Answer:
Cerium \({ }_{58} \mathrm{Ce}\) is the lanthanide having lowest atomic number.

Question 43.
Which halogen has the lowest electronegativity?
Answer:
Electronegativity of an atom decreases from top to bottom in a group. There fore, Astatine (At) has the lowest electronegativity of 2.2 (Pauling scale).

Question 44.
The atomic number of an element is 9. In which group should tt be placed in the modern periodic table?
Answer:
The electronic configuration of the element is 2,7. Since it has 7 electrons in its outermost shell, it should be placed in Group 17.

Question 45.
Name one element which was not known during Mendeleev’s time, but a place was left vacant in Mendeleev’s periodic table.
Answer:
The element is Germenium (Ge) which was not known during Mendeleev’s time, but its properties were predicted by Mendeleev and accordingly a place was kept vacant for it in his periodic table.

Short Answer Type Questions :

Question 1.
What is the necessity of arrangingrelements in the periodic table?
Answer:
Necessity of arranging elements in the periodic table It was observed from the early days that there were few groups of elements each of which had almost identical chemical and physical properties. So, a systematic arrangement of elements is essential since it is difficult to remember the individual properties of elements.

Question 2.
What is the ‘law of triads’?
Answer:
Law of triads (Dobereiner, 1817) : In a triad of elements having similar properties, the atomic weight of the central element was merely the arithmetic mean of the atomic weights of the other two elements.

Question 3.
What is the ‘law of octaves’ ?
Answer:
Law of octaves (Newlands, 1864) : If the elements are arranged in the increasing order of their atomic weights, the eighth succeeding element was the repetition of the first one like the 8 th note of musical scale i.e. first and similar characteristics.

Question 4.
What is Mendeleev’s periodic law ?
Answer:
Mendeleev’s periodic law (1869) : The physical and chemical properties of elements are the periodic function of their atomic weights.

Question 5.
What is modern periodic law ?
Answer:
Modern periodic law (Moseley) : It states that the physical and chemical properties of elements are the periodic function of their atomic numbers.

Question 6.
What is periodicity ?
Answer:
Periodicity : It is the recurrence of elements with similar properties after certain regular intervals when these are arranged in the increasing order of their atomic numbers.

Question 7.
Define group and period of modern periodic table.
Answer:
Period: The horizontal rows along which elements occur in the periocic table in ascending order of atomic number having dissimilar chemical properties are called periods.
Group: The vertical columns in which elements of similar physical and chemical properties occur in the periodic table are called groups.

Question 8.
How many periods and groups are present in Mendeleev’s periodic table and in the long form periodic table?
Answer:
Mendeleev’s periodic table contains seven periods and nine groups. Long form periodic table contains seven periods and eighteen groups.

Question 9.
What are the structural features of long or extended form of the periodic table (Bohr’s table)?
Answer:
Bohr’s table has the following features :
(i) All the elements have been arranged in the increasing order of atomic members.
(ii) Elements with similar electronic configurations have similar properties and hence have been placed together at one place.
The periodic table consists of :
(a) Seven horizontal rows called periods
(b) Eighteen vertical columns called groups or families.
(c) Four blocks (s, p, d, f)

Question 10.
What are the defects of long form of the periodic table ?
Answer:
Defects of long form of the periodic table :
(a) Position of hydrogen. It does not resemble fully with alkali metals but has been placed along with them. It also resembles halogens.
(b) Position of lanthanides and actinides are not proper in the periodic table.
(c) According to electronic configuration, helium should be placed in s-block where as it is placed in p-block.

Question 11.
What is atomic volume?
Answer:
Atomic volume : Atomic volume of an element is the volume in cm³ occupied by one gram atom of the element in the solid state and hence it is also called gram-atomic volume.

Question 12.
Explain how the atomic size of the elements change in periodic table?
Answer:
Atomic size : The distance of the outermost orbit from the nucleus of spherically shaped atom is called the atomic size.
The atomic size gradually decreases from left to right of the period upto the group VIIB, again increases in the end element.

Question 13.
What is Covalent radius ?
Answer:
Covalent radius : It is defined as one half of the distance between the centres of nuclei of two similar atoms held together by a purely covalent single bond.

Question 14.
What is Van der Waal’s radius?
Answer:
Van der Waal’s radius : It is defined as one half of the internuclear distance between two similar, adjacent atoms belonging to two neighbouring molecules of the same substance in the solid state.

Question 15.
What is metallic radius ?
Answer:
Metallic radius : It is defined as one half of inter-nuclear distance between two nearest metal atoms in a metallic lattice is called metallic radius.

Question 16.
What is ionic radius ?
Answer:
Ionic radius : It is defined as the effective distance from the nucleus of an ion upto which it has an influence in the ionic bond.

Question 17.
What is lonisation energy (IE) or lonisation potential (IP) ?
Answer:
lonisation energy or lonisation potential : First ionisation energy or simply ionisation energy (IE) is defined as the amount of energy required to remove one valence electron from an isolated neutral gaseous atom resulting in the formation of a monovalent positive ion.

Question 18.
What is electron affinity ?
Answer:
Electron affinity (EA) : First electron affinity or simply electron affinity is the amount of energy released when one electron is added to a neutral gaseous atom to form a monovalent negative ion.

Question 19.
What is the definition of electronegativity ?
Answer:
Elecironegativity (Pauling’s definition): It is the attractive force which an atom, bonded by a co-valent bond exerts on the bond pair of electrons responsible for the co-valent bond.
The electro-negativity of the elements increase from left to right of the periods in a periodic table.

Question 20.
What are s-block elements ?
Answer:
s-block elements : These are the elements of IA or 1 group (alkali metals; configuration n s¹ ) and IIA or 2 group (alkaline earth metals ; configuration n s² ). These are so named because the last electron in them enters s-oribitals.

Question 21.
What are p-block elements ?
Answer:
p-block elements These are the elements in which the last electron enters p-orbital of valence shell. The elements with configurations n s² n p¹ to n s² n p⁶ constitute this block. Thus p-block consists of elements of group IIIA(13), IVA(14), VA(15), VIA (16), VIIA (17) and zero group (18).

Question 22.
What are d-block elements ?
Answer:
d-block elements: These are the elements in which the last electron enters a (n-1) d orbital. These have configuration. (n-1) d^1-10 n s^0-2. This block is situated in between s and p-block elements. d-block elements are also called transition elements.

Question 23.
What are f-block elements ?
Answer:
f-block elements: These are the elements in which the last electron enters a ( n-2) f-orbital. Lanthanoids and actinoids constitute the f-block and are also shown separately at the bottom of the periodic table. They have (n-2)f^1-14 (n-1) d^1-10 n s² configuration. Elements of f-blocks are also called inner-transition elements.

Question 24.
What are inert gases or noble gases ?
Answer:
Inert gases or noble gases: The elements which belong to the group 18 of the periodic table are called inert gases or noble gases. They have 8 electrons (except He ) in their outermost shell. Therefore, their combining capacity or valency is zero. Hence, they are inert in nature.

Question 25.
What are representative elements ?
Answer:
Representative elements: The elements in which only the outer s or p-electron sub shell is incompletely filled are called representative or normal elements. Elements of s or p-blocks excluding the inert gases are included in this category. These elements have the outer electronic configuration from ns¹ to np⁵.

Question 26.
What are transition elements ?
Answer:
Transition elements: These are the elements in which the last shell is not completely filled. These elements have the configuration (n-1) d^1-9 ns^1-2 i.e., these elements contain 1-9 electrons in the penultimate shell and 1-2 electrons in the valence shell. The elements having unfilled or partially filled d-orbitals are named transition elements because these present a transition (change) from the most electro-positive elements to the most electro-negative elements.

Question 27.
What are inner transition elements ?
Answer:
Inner transition elements : Lanthanides \(\left({ }_{53} \mathrm{Ce}-{ }_{71} \mathrm{Lu}\right)\) and actinides \(\left({ }_{90} \mathrm{Th}-{ }_{103} \mathrm{Lw}\right)\) tare collectively known as inner transition elements. In these elements, three outermost shells are not completely filled. The last electron in them enters in the (n-2) subshell.

Question 28.
What is diagonal relationship?
Answer:
Diagonal relationship : Elements of second and third row which are present diagonally have similar properties because on moving along the diagonal, the decrease and increase of size, electropositive character and polarizing power partly cancel each other.

Question 29.
What is the IUPAC Nomenclature of elements (z >100) ?
Answer:
IUPAC Nomenclature of elements (z >100) : Elements with atomic number beyond 100(z >100) have been named according to IUPAC system, which is connected with the elements atomic number. The first two letters tell us how many hundred (e.g. Un = one) the next three how many tens (e.g. nil = 0 ) the rest units (e.g. quad = 4, pent = 5, hex = 6, hept = 7 and so on).

Question 30.
Ca²+, K⁺, Cl^– have 18 extra nuclear electrons. How will they be arranged in the increasing order of size?
Answer:
Explanation : Size of iso-electronic ions decreases with increase in atomic number. Therefore increasing order of size is :
Ca²⁺< K⁺< Cl^–< S^2-

Question 31.
Explain the reason why the first ionization energy of Na is smaller than that of Mg and second ionisation energy of Mg is smaller than that of Na.
Answer:
Explanation : Electronic configuration of Na and Mg are 1s² 2s² 2p⁶ 3s¹ respectively. Therefore magnesium has higher first ionization potential than Na due to its higher value of nuclear charge and more stable configuration (fully filled s-orbital).
After removal of one electron, Na⁺ and Mg⁺ ions have configuration 1s² 2s² 2p⁶ and 1s² 2s² 2s² p⁶ 3s¹ respectively and now it will be easier to remove 3s¹ electron rather than electron is lower than that of Na.

Question 32.
Differentiate between covalent radius and Van der Wal’s radius.
Answer:
Difference between Covalent radius and Van der Waal’s radius : Covalent radius is one half of the distance between the centres of nuclei of two similar atoms held together by a purely covalent bond but van der waal’s radius is one half of the inter-nuclear distance between two similar adjacent atoms belonging to two neighbouring molecules of the same substance in the solid state.

Broad Answer Type Questions :

Question 1.
State the different periods with the elements.
Answer:
The different period swith the elements :

Question 2.
What are group and sub-groups?
Answer:
Groups : Mendeleev’s periodic taule shows that the elements with related chemical properties fall in c ne below the other forming vertical columns called groups. There are nine groups from group I to group VIII and 0 (zero). Sub-groups : Each of the groups from I to VII has been divided into two sub-groups A and B.

Question 3.
What are called alkali metals ? In which group do they belong ? State the similarity of their chemical properties.
Answer:
Alkali metals : Lithium (Li), Sodium (Na), Potassium (K), Rubidium (Rb) and Caesium (Cs). These five metals are generally known as alkali metals. Position in periodic table: The alkali metals are included in the A subgroup of the first group (IA).
Similarity : (i) Alkali metals are strong electro positive.
(ii) The oxides of these metals are strongly basic.
(iii) Each has valency 1.

Question 4.
Where are the inert gas elements placed and why ?
Answer:
Position of inert gas elements in periodic table : He, Ne, Ar, Kr, Xe, and Rn. These are inert elements. They are each gaseous and monoatomic. These are chemically non-reactive. As these elements do not react, these have zero valency.
So they are included in 0 (zero) group of the periodic table.
Besides Helium, all the inert gases have eight (8) electrons in their outermost orbit. There are only 2 electrons in the outermost orbit of Helium.

Question 5.
What are halogen elements ? In which do they belong ?
Answer:
Halogen elements : The four strongly electro-negative non-metals fluorine (F), chlorine (Cl), bromine (Br) and iodine (I) form a family of closely allied elements known as the halogens meaning literally sea salf-producer as these elements react with most metals to form compounds similar to sea-salt, sodium chloride. Position in periodic table: Halogen elements are placed in group VIIB of periodic table. The electro-negative character of the elements increases from left to right in a period. So, the strongly electronegative elements are in the almost extreme right group i.e. in group VIIB of the periodic table.

Question 6.
Discuss the position of hydrogen in periodic table.
Answer:
Position of hydrogen in periodic table :
Reasons for placing in group IA :

1. Like the alkali metals, hydrogen is electro-positive.
2. Valency of hydrogen is I, alkali metals are also mon-valent.
3. During electrolysis of a fused chloride of an alkali metal, the alkali metal deposits at the cathode; in the electrolysis of dilute aqueous solution of hydrogen chloride, hydrogen collects at the cathode.
4. Like the alkali metals, hydrogen has reducing property and forms stable oxide, like water (H₂O).
5. Like hydrogen, each of the alkali metals, Li, Na, K, Rb, Cs, Fr possesses one valence-electron.

Reasons for placing in Group VIIB :

(i) Like the halogens, hydrogen is a non-metallic element.
(ii) Valency of hydrogen and that of each halogen is 1.
(iii) Halogen molecules are diatomic, a hydrogen molecule is also diatomic.
(iv) The halogens from metallic halides like, NaCl, KBr, Kl etc. Hydrogen also produces salt-like hydrides like LiH, NaH, CaH₉ etc with the strongly electropositive elements and hydrogen here acts as an electro-negative element.
(v) Atoms of halogen elements may transform to negative halide ions by taking one electron each. (e.g. X + e → X^– ; X = F, Cl, Br, I) and hydrogen atom also may transform to a negative hydride ion by capturing oen electron : H + e → H^–.
(vi) Like the hologens, hydrogen also can produce covalent comj unds reacting with electro-negative elements like S, O etc.
Due to such varied tendency for occupying a seat in the periodic table, hydrogen is often called a naughty element or a rogue elements.

Question 7.
Draw a diagram by which change of periodic properties are shown.
Answer:
Diagram.