NCERT solution for class 10// Science // Chapter 5 - Periodic classification of elements
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NCERT solution for class 10 // Science // Chapter 5 - Periodic classification of elements
Chapter 5 - Periodic classification of elements
Page number 81
Q1. Did Dobereiner's triads also exist in the columns of newlands octaves compare and find out ?
Answer - Dobereiner's triads also exist in the column of newland octaves
Ex- Lithium ( Li) , Sodium (Na) and Potassium(K) institute of trades if we consider Li as a first element then the eight element from it is Na and if we consider Na as the first element then the eight element from it is K
Q2. What were the limitations of Dobereiner's classification
Answer -
- Dobereiner's only form 3 traits from the elements known at that time
- The classification of known elements could not be possible on the basis of Dobereiner's traits
Q3. What were the limitations of Newlands law of octaves ?
Answer
The Newland law of octaves has following limitations
- This law was applicable only upto calcium after calcium every at element did not possess the same properties similar to first one.
- Newland assume that only 56 elements existed in nature and no more elements would be discovered in future
- In order to fit elements into his stable new learns at just two elements in the same slot and also put some unlike elements under the same column
- Ex. - Cobalt and nickel are in the same slot
Page number 85
Q4. Use Mendeleev 's periodic table to predict the formula for the oxides of the following element
K, C , Al ,Si ,Ba
Answer
Element K - Formula of its oxide is K2O
Element C - Formula of its oxide is CO2
Element Al - Formula of its oxide is Al2 O3
Element Si- Formula of its oxide is SiO2
Element Ba - Formula of its oxide is BaO
Q5. Besides gallium which other elements have since been discovered that were left by Mendeleev periodic table (any two) ?
Answer - Scandium in Germanium were the two elements that have been discovered letter to fit in the space left in Mendeleev periodic table
Q6. What were the criteria used by Mendeleev in creating his periodic table ?
Answer - The arrangement of elements in increasing order of atomic masses
Similarity in chemical properties of element
Q7. Why do you think the noble gases are placed in a separate group ?
Answer - Noble gases have a complete octet hence they are very stable they are also called in inert gases they do not react with other elements due to their stability so they are placed in a separate group
Page number 90
Q8. How could the modern periodic table remove various anomalies of Mendeleev periodic table ?
Answer -
- Modern periodic table is based on the atomic number
- Isotopes have a a same atomic number and chemical properties so they are put in a same group in periodic table
- The order of heavy and lighter elements like Cobalt and nickel arranged correct which was not in Mendeleev periodic table
- In modern periodic table the hydrogen is kept on the top left corner due to its unique characteristics
- Inert gases are placed in a 18th group
Q9. Name two elements you would expect to show chemical reactions similar to magnesium what is the basis for your choice ?
Answer - Calcium (Ca) and Beryllium ( Be) both are belong to Magnesium group and they have 2 valence electrons
All these three elements belong to same group and show similar properties
Q10. Name
a) Three elements that have a single electron in their outermost shells
b) Two elements that have two electrons in their outermost shells
c) Three elements with filled outermost shells
Answer -
a) lithium (Li), Sodium;(Na) , Potassium (K)
b) Magnesium (Mg), Calcium (Ca)
c) Helium (He), Neon (Ne) ,Argon ( Ar)
Q11. a) Lithium Sodium potassium are all metals that react with water to liberate hydrogen gas is there any similarity in the atoms of these elements .
b) Helium is an unreactive gas and neon is a gas of extremely low reactivity what if anything do their atoms have in common .
Answer - a) Li , Na and K have one electron in their outermost shell so they belong to group I of the periodic table
Li- atomic number- 3 -
electronic configuration (2, 1)
Na- Atomic number -11
Electronic configuration -( 2,8,1 )
K- atomic number -19
Electronic configuration -(2 ,8 ,8, 1)
b) Helium and Neon both have completely filled outermost shell
He atomic number - 2
Electronic configuration -( 2 )
Ne atomic number - 10
Electronic configuration -(2 ,8)
Q12 . In the modern periodic table which are the metals among the first 10 elements
Answer - In modern periodic table lithium and beryllium among the first 10 elements
Q13. By considering their position in the periodic table which one of the following elements would you expect to have maximum metallic characteristics .Ga, Ge, As, Se, Be
Answer - Above elements belong to same periods so from moving left to right size of element decreases due to increase its nuclear charge and the tendency of lose of electron decreases so the metallic character of element also decreases.
Ga> Ge> As > Se > Br - metallic character decreases
Exercise
Q1. Which of the following statement is not a correct statement about the trends when going from left to right across the period of periodic table
a) The elements become less metallic in nature
b) The number of valence electron increases
c) The atom lose their electrons more easily
d) The oxides become more acidic
Answer - The atoms lose their electrons more easily
Q2. Element X form of chloride with the formula X cl2 which is a solid with a high melting point x would most likely be in the same group of the periodic table as
a) Na. b) Mg. c) Al. d) Si
Answer - Mg
Q3. Which element has
a) Two shells both of which are completely filled with electrons
b) Electronic configuration 282
c) Total of three shells with four electrons in its valence shell
d) Total of two shells with three electrons in its valence shell
e) Twice as many electrons in its second shell as in its first shell
Answer - a) Noble gases
b) Magnesium atomic number -12
c) Silicon atomic number- 14
d) Boron atomic number- 5
e) Carbon atomic number -6
Q4. a) What property do all elements in the same column of the periodic table as boron have in common .
b) What property do all elements in the same column of periodic table as fluorine have in common
Answer a) Boron is from group 13 in periodic table show all elements of group 13 in which boron is present have 3 electrons in their valence shell.
b) Fluorine is from the group 17th all elements from this group have 7 electron in their valence shell so they have one valence
Q5 . An atom has electronic configuration -(2, 8 ,7)
a) What is the atomic number of this element
b ) To which of the following elements would it be chemically similar ( atomic numbers are given in parentheses)
N (7). , F( 9). ,P (15). , Ar (18)
Answer - a) Atomic number of the element = 2 + 8 + 7 =17
b) N atomic number -7
Electronic configuration- (2,5)
F atomic number- 9
Electronic configuration -(2 ,7)
P atomic number -15
Electronic configuration -(2 ,8 ,5)
Ar atomic number-- 18
Electronic configuration -(2 ,8 ,8 )
It is similar to fluorine because fluorine also contains 7 electron in its valence shell
Q 6. The position of three elements A B and C in the periodic table are shown below .
|
Group
16 |
group |
|
17 -. |
- |
|
- |
- |
|
- |
B |
|
B. |
- |
|
- |
C |
a ) state whether A is a metal or nonmetal
b) state whether C is more reactive or less reactive than A
c) will C be larger or smaller in size than B
d ) which type of ion cation or anion will be formed by element A
Answer -
a) A is non metal
b) C is more reactive than A
c) Size of C is smaller than that of B
d) Element A will form anion
Q7 . Nitrogen (atomic number 7) and phosphorus (atomic number 15 ) belong to group 15 of the periodic table write the electronic configuration of these two elements which of these will be more electronegative why ?
Answer -
Atomic number of Nitrogen is -7
Electronic configuration of Nitrogen - (2,5)
Atomic number of Phosphorus is -15
Electronic configuration of Phosphorus is- (2,8,5)
Hence and N will be more electronegative than p s electronegativity decreases on going down a group
Q 8 . How does the electronic configuration of an atom relate to its position in the modern periodic table
Answer - From the electronic configuration the group number and period number of the atoms elements is identify and the position of the atom is determined
Ex - Na atomic number -11
Electronic configuration of Na- K -2 , L -8, M-1
It has one electron in its last share so it belongs to group 1 in periodic table 3 shells of the electronic configuration are filled in an a so it is from third period
Q9 . In the modern periodic table calcium (atomic number 20) surrounded by elements with atomic number 12, 19, 21 and 38 which of these have a physical and chemical properties resembling calcium
Answer
In modern periodic table Calcium atomic number 20
Electronic configuration - (2, 8, 8 ,2 )
Magnesium atomic number 12
Electronic configuration -( 2 ,8 ,2)
Potassium atomic number 19
Electronic configuration -(2, 8 ,8 ,1)
Scandium atomic number 21
Electronic configuration -(2, 8, 8 ,3 )
Stronsium atomic number 38
Electronic configuration- (2, 8, 18 ,8, 2).
From the above electronic configuration we can see that the element with atomic number of 12 and 38 have two electrons in their last shell like calcium so they will be resemble with calcium in their physical and chemical properties
Q10 . Compare and contrast the arrangement of elements in Mendeleev periodic table and in modern periodic table ?
Answer
Mendeleev periodic table
- Arrangement of elements is on the basis of atomic masses
- Inert gases are absent
- It has 6 period and eight groups
- Transition elements are not separated
- Lanthanoids and actinoids are absent
Modern periodic table
- Element are arranged on the basis of atomic number
- Inert gases are located in a separate group
- It has 7 periods and 18 groups
- Transition elements are placed in a separate group
- Lanthanoids and actinoids are present at the bottom of the table
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