Page 118 - ICSE Chemistry 8
P. 118

B.  Read the following paragraph. Iden  fy the incorrect parts.
                      Valency refers to the exchanging capacity of an atom of a compound. The valency of an element is
                      always a whole number that varies from 0 to 6. The outermost shell of an atom is called the electron
                      shell and the electrons present in the electron shell are called valent electrons. Lithium and sodium are
                      divalent elements. Oxygen and magnesium are monovalent elements. Boron and aluminium are trivalent
                      elements. Silicon is a pentavalent element.

                 C.  Answer in detail.
                       1.  Write the rules that are applied for represen  ng the elements.

                       2.  How is the chemical formula of a compound derived? Explain with the help of an example.
                       3.  State the ways in which we can balance a chemical equa  on. Also give examples.
                       4.  Write the informa  on gathered from a chemical equa  on.

                       5.  Discuss the limita  ons of a chemical equa  on.


                  OBSERVE AND PERFORM

                   Observe the given table carefully and answer the following ques  ons.

                                        Element             Valency           Element             Valency
                                        Nitrogen              3, 5               Iron               2, 3

                                      Phosphorus              3, 5             Cobalt               2, 3

                                        Sulphur             2, 4, 6            Copper               1, 2
                                        Chlorine           1, 3, 5, 7           Iodine            1, 3, 5, 7

                                       Manganese          2, 3, 4, 6, 7         Lead                2, 4

                       1.  Name the elements exhibi  ng valency 3 and 5 both. Write their symbols.

                       2.  Write the symbols of the elements exhibi  ng valency 2 and 3 both.
                       3.  Name the elements exhibi  ng valency 2, 4 and 6. Write their symbol.

                       4.  Name the elements exhibi  ng valency 1, 3, 5 and 7. Write their symbol.
                       5.  Write the symbol of the element exhibi  ng valency 2, 3, 4, 6 and 7.





                   APPLY YOUR LEARNING                                        LIFE SKILLS

                   A.  What is the valency of the element represented         In a group of two or three students, make
                      using the symbol Mg?                                    a chart that depicts important and simple
                   B.  What is the La  n name of the element represented      chemical equa  ons showing the physical
                      using the symbol Cu?                                    states of the reactants and products.
                   C.  What is the chemical formula and valency of the        (Team work and Coopera  on)
                      radicals: phosphate and bisulphate?




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