Class 10 Science Chapter 5 Periodic Classification of Elements

Class 10 Science Chapter 5 Periodic Classification of Elements The answer to each chapter is provided in the list so that you can easily browse throughout different chapters NCERT Class 10 Science Chapter 5 Periodic Classification of Elements and select need one.

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Class 10 Science Chapter 5 Periodic Classification of  Elements

Also, you can read the SCERT book online in these sections Solutions by Expert Teachers as per SCERT (CBSE) Book guidelines. These solutions are part of SCERT All Subject Solutions. Here we have given Assam Board Class 10 Science Chapter 5 Periodic Classification of Elements Solutions for All Subjects, You can practice these here…

Periodic Classification of  Elements

Chapter – 5

GENERAL SCIENCE

TEXTUAL QUESTIONS AND ANSWERS

Page – 81 

Q.1. Did Dobereiner’s triads also exist in the columns of Newlands Octaves ? Compare and find out.

Ans :- Dobereiner’s triads are also found in Newland’s octave . For example , Li , Na , k . 

Q.2. What the limitations of Dobereiner’s classification ? 

Ans :- The limitation of Dobereiner’s classification was that it failed to arrange all the taken known elements in the form of triads of elements having similar chemical properties . Dobereiner could identify only three triads from the elements known at that time . So , his classification of elements was not much successful . 

Q.3. What were the limitations of Newland’s law of octaves ? 

Ans :- Newlands ‘ law of octaves for the classification of elements has the following limitations : 

( i ) Newlands ‘ law of octaves was applicable to the classification of elements up to calcium only . After calcium every eight elements did not posses the properties similar to that of the first element . Thus Newlands ‘ law of octaves worked well with lighter elements only. 

( ii ) Newands ‘ assumed that only 56 elements existed in nature bet and no more elements would be discovered in the future . But later on , several new elements were discovered whose proportics did not fit into Newlands , law of octaves . 

( ii ) In order to fit elements into his table , Newlands put even two elements together in one slot and that too in the column of unlike elements having very different properties . 

( iv ) Iron element which resembles cobalt and nickel elements in properties was placed far away from these elements . 

Page – 85

Q.1. Use Mendeleev’s periodic table to predict the formula for the oxides of the following elements : 

K , C , AI , Si , Ba 

Ans :- ( i ) The element K is in group 1 of Mendeleev’s periodic table is which the general formula of the oxides of elements is R₂ O . So , the formula of oxide of K will be K₂ O . 

( ii ) The element C is in group IV of Mendeleev’s periodic table in which the general formula of the oxides of elements is RO₂So , the formula of oxide of C will be CO₂.

( iii ) The element Al is in group III of Mendeleev’s periodic table in which the general formula of the oxides of elements is R₂O₃ . So the formula of oxide of Al will be Al₂O₃. 

( iv ) The element Si is in group IV of Mendelev’s periodic table in which the general formula for the oxides of elements is RO₂ So , the formula of the oxide of Si will be SiO₂.

( v ) The element Ba is in group II of Mendeleev’s periodic table in which the general formula for the oxides of elements is RO . So , the formula of oxide of Ba will be BaO . 

Q.2. Besides gallium , which other elements have since been discovered that were left by Mendeleev in this periodic table ? ( any two ) 

Ans :- Scandium and Germanium . 

Q.3. What were the criteria used by Mendeleev in creating his periodic table ? 

Ans :- When mendeleev started his work 63 elements were known . He examined the relationship between the atomic masses of the elements and their physical and chemical properties . 

Among chemical properties , Mendeleev concentrated on the compounds formed by elements with oxygen and hydrogen . He selected hydrogen and oxygen as they are very reactive and formed compounds with most elements . The formula of the hydrides and oxides formed by an element were treated as one of the basic properties of an element for its classification . He then took 63 cards and on each card he wrote down the properties of one element . 

He sorted out the elements with similar properties and pinned the cards together on a wall . He observed that most of the elements got a place in a periodic table and were arranged in the order of their increasing atomic masses . It was also observed that there occurs a periodic recurrence of elements with similar physical and chemical properties . On this basis Mendeleev formulated a periodic law . Which states that ” The properties of elements are the periodic function of their atomic masses .

Q.4. Why do you think the noble gases are placed in a separate group ? 

Ans :- Noble gases like helium , neon and argon are chemically inert and are present in atmosphere in extremely low concentrations . Thus owing to their similar inert behaviour and similar electronic configuration . They are justified to be placed in a separate group . 

Page – 90 

Q.1. How could the Modern Periodic Table remove various anomalies of Mendeleev’s Periodic Table ? 

Ans :- Since all the isotopes of an element have the same atomic number . They can be put at one place in the same group of the periodic table . For example , both the isotopes of chlorine . Cl – 35 and Cl -37 , have the same atomic number of 17. so both of them can be put at one place in the same group of the periodic table . 

The atomic number of cobalt is 27 and that of nickel is 28 . Now , according to modern periodic law , the elements are arranged in the order of increasing atomic numbers . So , cobalt with lower atomic number ( 27 ) should come first and nickel with higher atomic number (28 ) should come later , even if their atomic masses are in the wrong order. 

Q.2. Name two elements you would expect to show chemical reactions similar to magnesium . What is the basis of your choice ? 

Ans :- Beryllium and Calcium . Both Beryllium and calcium have some electrons in outermost shell with calcium , i.e. in outermost shell they have two electrons each . 

Q.3. 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 . 

Ans :- ( a ) Lithium , sodium , potassium.

          ( b ) Magnesium , calcium . 

          ( c ) Helium , Neon , Argon . 

Q.4. ( 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 in a gas of extremely low reactivity . What if anything , do their atoms have in common ? 

Ans :- ( a ) The atoms of lithium , sodium , potassium all have only one electron in their outer most shells . 

( b ) The atoms of helium and neon have their outer most shell completely filled . 

Q.5. In the Modern Periodic Table , which are the metals among the first ten elements ? 

Ans :- Li , Be and B are metals . 

Q.6. By considering their position in he periodic table , which one of the following elements would you expect to have maximum metallic characteristic ? 

Ga , Ge , As , Se , Be 

Ans :- Be . 

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