ICSE Selina Concise Solutions for Grade 10  
                                                   Chemistry 
               Chapter 1. – Periodic Table, Periodic Properties and variations of 
                                                   Properties 
            
           1. (i) State modern periodic law. 
           Ans:  "The  properties  of  elements  are  periodic  functions  of  their  atomic  number," 
           according to the modern periodic law. 
           (ii) Name the scientist who stated the law. 
           Ans: The periodic law was proposed by Henry Moseley. 
           (iii) How many groups and periods does modern periodic table have? 
           Ans: Modern Periodic table has 7 periods and 18 groups. 
            
           2. What are horizontal rows and vertical columns in a periodic table known as? 
           Ans: In the periodic table, the horizontal rows are known as periods, while the vertical 
           columns are known as groups. 
            
           3. Periodicity is observed due to the similar............. 
           (number of valence electrons/ atomic number/ electronic configuration) 
           Ans: Periodicity is observed due to the similar electronic configuration. 
            
           4. How does electronic configuration in atoms change 
           (i) In a period from left to right? 
           Ans: While the number of shells remains constant, the number of valence electrons 
           rises by one as we move from left to right over any given period. 
           (ii) In a group top to bottom? 
           Ans: The number of shells rises sequentially, one by one, from top to bottom in a 
           group, but the number of valence electrons remains constant. 
            
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           5. Name 2 elements in each case: 
           (i) Alkali metals 
           Ans: Sodium and Potassium 
           (ii) Alkaline earth metals 
           Ans: Calcium and Magnesium 
           (iii) Halogens 
           Ans: Chlorine and Bromine 
           (iv) Inert gas 
           Ans: Neon and Argon 
            
           6. Elements of group 1 and elements of group 17 both have valency1. Explain. 
           Ans: The combining capability of an element's atom is known as valency. It's the 
           number of electrons that an atom can provide, take, or share. It's merely a number with 
           no positive or negative sign attached to it. 
           The outermost orbital  of  Group  1  elements  has  one  electron,  while  the  outermost 
           orbital  of  Group  7  elements  has  seven  electrons.  The  number  of  electrons  in  the 
           outermost shell determines the valency (i.e. valence shell). If the outermost shell has 
           only one electron, it can contribute one electron while interacting with other elements 
           to form a stable electronic configuration. If the outermost shell has seven electrons, its 
           valency is one (8 - 7 = 1) since it may accept one electron from the combining atom. 
           The number of electrons in the valence (outermost) shell rises from left to right in a 
           given period. However, the valency grows only until Group 14, when it becomes 4, 
           and then drops, becoming 1 in Group 17. 
            
           7. Correct the statements. 
           (i) Elements in the same period have equal valency. 
           Ans: Elements in the same group have equal valency. 
           (ii) Valency depends upon the number of shells in an atom. 
           Ans: Valency depends upon the number of valence electrons in an atom. 
           (iii) Copper and zinc are representative elements. 
           Ans: Copper and zinc are transition elements. 
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           (iv) Transition elements are placed at the extreme right of the periodic table. 
           Ans: Noble gases are placed at the extreme right of the periodic table. 
            
           8. What do you understand by? 
           (i) Periodicity 
           Ans:Periodic  qualities  are  properties  that  return  at  regular  intervals  or  have  a 
           progressive variation at regular intervals, and the phenomenon is known as periodicity 
           of elements. 
           (ii) Typical elements 
           Ans:  The  third-period  elements  Na,  Mg,  Al,  Si,  P,  and  Cl  are  known  as  typical 
           elements because they summarise the features of their respective groups. 
           (iii) Orbits 
           Ans: The orbits or shells in which elements circle around the nucleus are known as 
           orbits or shells. 
            
           9.  Name  2  elements  you  would  expect  to  show  chemical  reactions  similar  to 
           calcium. What is the basis of your choice? 
           Ans: Beryllium and magnesium will have chemical interactions that are similar to 
           those of calcium. Because these elements, like calcium, belong to the same group 2 
           and have two electrons in their outermost shell. 
            
           10. Name the (i) metals, (ii) metalloids and (iii) non-metals in the first twenty 
           elements. 
           Ans:  Metals:  Lithium,  Beryllium,  Sodium,  Magnesium,  Aluminium,  Potassium, 
           Calcium 
           Metalloids: Boron, Silicon 
           Non-metals:  Hydrogen,  Helium,  Carbon,  Nitrogen,  Oxygen,  Fluorine,  Neon, 
           Phosphorous, Sulphur, Chlorine, Argon  
            
           11. Fluorine, Chlorine and Bromine are put in one group on the basis of their 
           similar properties. 
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           (i) What are those similar properties? 
           Ans:  Non-metallic,  highest  electronegativity,  highest  ionisation  potentials,  and 
           maximum electron affinity in respective periods. 
           (ii) What is the common name of this group or family?  
           Ans: The common name is halogens, as they are salt forming elements. 
            
           12.  What is  the  main  characteristic  of  the  last  element  in  each  period  of  the 
           Periodic Table? What is the general name of such elements? 
           Ans: The last element in each period of the periodic table has the property of being 
           inert  or  chemically  unreactive.  These  elements  are  referred  to  as  "Noble  gases"  in 
           general. 
            
           13. According to atomic structure, what determines which element will be the 
           first and which will be the last in a period? 
           Ans: The quantity of valence electrons defines the first and final element in a period, 
           according to atomic structure. 
            
           14. How does the number of: 
           i. Valence electrons and 
           ii. Valency vary on moving from left to right in the third period of the periodic 
           table? 
           Ans: 
           i. In the third period of the periodic table, the valence electrons grow from 1 to 8. 
           ii. The valency climbs from 1 to 4 and then lowers from 4 to 0 as you move from left 
           to right. 
            
           15. Name the type of elements, which have their 
           (i) Outermost shell complete 
           Ans: Noble gases 
           (ii) Outermost shell incomplete 
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