The Periodic Table Exe-5C Descriptive Answer Chemistry Class-9 ICSE Selina Publishers

The Periodic Table Exe-5C Descriptive Answer Chemistry Class-9 ICSE Selina Publishers Solutions Chapter-5. Step By Step ICSE Selina Concise Solutions of Chapter-5 The Periodic Table with All Exercise including MCQs, Very Short Answer Type, Short Answer Type, Long Answer Type, Numerical and Structured/Application Questions Solved . Visit official Website CISCE for detail information about ICSE Board Class-9.

The Periodic Table Exe-5C Descriptive Answer Chemistry Class-9 ICSE Concise Selina Publishers

Board ICSE
Publications Selina Publication
Subject Chemistry
Class 9th
Chapter-5 The Periodic Table
Book Name Concise
Topics Solution of Exercise – 5C Descriptive Answer type
Academic Session 2023-2024

Exercise – 5C Descriptive Answer type

The Periodic Table Class-9 Chemistry Concise Solutions  

Page-101

Question 1.

(a) State the nature of compounds formed when group 17 elements combine with (i) metals (ii) non-metals.

(b) Why group 17 elements are highly reactive?

Answer:

(a)

Group 17 elements react with metals to form metal halides which are neutral in nature.

Group 17 elements react with non-metals to form acidic compounds such as hydrogen halides.

(b) Group 17 elements are highly reactive because of their closeness to the noble or stable gas configuration. They can easily achieve a noble gas electron structure.

Question 2.

(a) What is the name given to group 17 elements? Why are they called so?

(b) Comment on the (i) reactivity (ii) colour (iii) physical state of group 17 elements.

Answer:

(a) Group 17 elements are called halogens. The name halogens is from Greek halo (sea salt) andgens (producing, forming) and thus means ‘sea salt former’.

(b) and Group 17 elements or halogens:

Reactivity: Halogens are the most reactive non-metals, their reactivity decreases down the group. Fluorine is the most reactive halogen and iodine is the least reactive halogen.

Colour: Fluorine is a pale yellow gas, chlorine is a greenish yellow gas, bromine is a reddish brown liquid and iodine is a violet solid.

Physical state: Gaseous

Question 3.

State the uses of Modern Periodic table.

Answer:

(i) Periodic table has been useful in predicting the existence of new elements.

(ii) It has been useful in the past in correcting the position of elements in relation to their properties.

(iii) Study of elements and their compounds has become systematic and easier to remember.

(iv) Position of an element in the periodic table reveals its:

  • atomic number
  • electronic configuration
  • number of valence electrons
  • properties

(v) Nature of chemical bond, formula of compound formed and properties of that compound can all be predicted from the periodic table.

(vi) Position of an element in the periodic table reveals:

  • valency of the element
  • whether the element is a metal or a non-metal — metals occupy the extreme left positions of the periodic table while non-metals are at the extreme right of the periodic table.

Question 4.

Give the merits of Mendeleev’s periodic table.

Answer:

Merits of Mendeleev’s periodic table :

(i) Grouping of elements — He generalized the study of the elements then known to a study of mere eight groups.

(ii) Gaps of undiscovered elements — Mendeleev left some gaps in his periodic table for subsequent inclusion of elements not known at that time.

(iii) Prediction of properties of undiscovered elements — He predicted the properties of then unknown elements on the basis of the properties of elements lying adjacent to the vacant slots.

(iv) Incorrect atomic mass corrected — He was able to correct the atomic mass of elements like gold and platinum by placing these elements strictly on the basis of similarities in their properties.

Question 5.

State the defects of the table proposed by Mendeleev.

Answer:

Defects of table proposed by Mendeleev:

(i) Anomalous pairs — The following elements did not follow Mendeleev’s principles:

  1. Argon with atomic mass 39.9 precedes potassium with atomic mass 39.1
  2. Cobalt with atomic mass 58.9 precedes nickel with atomic mass 58.6
  3. Tellurium with atomic mass 127.6 precedes iodine with atomic mass 126.9

(ii) Position of isotopes — According to Mendeleev’s periodic table isotopes should be given separate place in the table since they have different atomic mass. But they were not assigned separate places.

(iii) Grouping of chemically dissimilar elements — Elements such as copper and silver bear no resemblance to alkali metals (lithium, sodium etc.) but they have been placed together in the first group.

(iv) Separation of chemically similar elements — Elements that are chemically similar, such as gold and platinum have been placed in separate groups.

(v) Electron arrangement — It does not explain the electron arrangement of elements.

(vi) Position of hydrogen — Hydrogen was not given a fixed position. It was considered in group IA as well as in group VIIA because it forms forms both a positive ion, viz. in HCl and a negative ion, viz. in NaH.

Question 6.

Give the main characteristics of representative elements.

Answer:

(i) They include both metals and non-metals. There is a regular gradation from metallic to non-metallic character as one moves from left to right across the period.

(ii) They form electrovalent as well as covalent compounds with non-metals.

(iii) Metallic nature increases on moving down any of these seven groups.

(iv) Metals, which are good conductors of heat and electricity, are present in groups 1 and 2. Non-metals, which are present in groups 16 and 17, are poor conductors of heat and electricity.

(v) Some heavier elements, like tin and lead, exhibit variable valencies.

Question 7.

Discuss the characteristics of halogens with respect to:

(a) reactivity

(b) intensity of colours

(c) formation of ions.

Answer:

(a) Halogens are the most reactive non-metals. Their reactivity decreases down the group. For example: fluorine is the most reactive and iodine is the least reactive.

(b) The intensity of the colour of the element increases from pale to dark. Fluorine is a pale yellow gas, chlorine is a greenish-yellow gas, bromine is a reddish-brown liquid and iodine is a violet solid.

(c) They all form negative ions carrying a single charge [Fluoride ions F, Chloride ions Cl, Bromide ions Br, Iodide ions I.]

Question 8.

Two elements ‘P’ and ‘Q’ belong to the same period of the modern periodic table and are in group 1 and group 2 respectively. Compare the following characteristics in tabular form.

(a) number of electrons in their valence shell.

(b) their tendency to lose electrons.

(c) their metallic characters.

(d) formation of their oxides.

(e) formulae of their chlorides.

Answer:

As elements P and Q belong to the same period of the modern periodic table and are in group 1 and group 2, they belong to alkali metals and alkaline earth metals, respectively.

Characteristic Alkali metals (Element P) Alkaline earth metals (Element Q)
(a) Number of electrons in their atoms Valence electron = 1 Valence electrons = 2
(b) Their tendency to lose electrons Can easily lose electrons They will lose electrons easily but not as easily as alkali metals can.
(c) Formation of their oxides React rapidly with oxygen in air

4Na + O2 → 2Na2O

Less reactive than alkali metals
(d) Formulae of their chlorides NaCl, KCl, CsCl MgCl2, CaCl2, BaCl2

 

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