Q24 of 24 Page 5

a. The following is a list of the electron distributions of atoms of unknown elements.


Choose an element from the list for each of the following descriptions.


i. It is a noble gas.


ii. It is a soft metal with a low density.


iii. It has giant covalent structure similar to diamond.


iv. It can form a negative ion of the type X3-.


b. How does electronic configurations of atoms change in a period with increase in atomic number? (CBSE 2012)

(a) (i) We know that noble gases have complete octet so element D is noble gas.


(ii) Element E is soft metal with a low density. Element E is Rubidium because its atomic number is 37.


(iii) Element B has giant covalent structure similar to diamond because element B has 4 valence shell electrons like carbon.


(iv) Element A can form a negative ion of the type X3- because element A has 5 electrons in outermost shell and it requires 3 electrons to acquire noble gas configuration.


(b) On increasing the atomic number, the number of electrons in valence (outermost) shell increases but number of shells will be same in all atoms of a period.


Ex- The elements of 2nd period are


Li3 = 2, 1


Be4 = 2, 2


B5 = 2, 3


C6 = 2, 4


N7 = 2, 5


O8 = 2,6


F9 = 2, 7


Ne10 = 2, 8

More from this chapter

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20

Define the following terms:(i) Valency; (ii) Atomic size(b) How do the valency and' the atomic size of the elements vary while going from left to right along a period in the modern periodic table? (CBSE 2014)

 21

The elements of a period of the periodic table are given in order from left to right with one of its element missing:

Na        Mg       Al       Si        S      Cl      Ar 

a. To which period do these elements belong?


b. One element of this period is missing. Which is the missing element and where should it be placed?


c. Which one of these elements in this period shows the property of catenation?


d. Which one of these elements is least reactive? (CBSE 2008)

 22

In the following table,

The position of some elements A,B,C,D,E,F and G in the Modern Periodic Table is given as under:



a. In which group are inert elements placed?


b. What type of ions would B, C, E and F form?


c. Which elements would have chemical properties similar to C?


d. How many shells would A have?


e. What is the similarity between A and D?


f. Identify the most abundant element in the earth’s crust. (CBSE 2008)

 23

(i) The position of three elements A,B and C in the periodic table are shown below-


(a) State whether A,B and C is a metal or non-metal.


(b) State whether Cis more reactive or less reactive than A.


(c) Will B be larger or smaller in size than A .


(d) Which type of ion, cation or anion, will be formed by element A,B and C.


(e) Write the electronic configuration A, B and C. (CBSE 2010)