2B - Review

           1.   This question is about different models of bonding and molecular shapes.  Magnesium sulfide shows ionic bonding.

                 (i)      What is meant by the term ionic bonding?  [1]  (Electrostatic) attraction between oppositely charged ions

                (ii)      Draw a ‘dot-and-cross’ diagram to show the bonding in magnesium sulfide. Show outer electron shells only.  [2] 

                        Mg shown with either 8 of 0 electrons  AND  S shown with 8 electrons with 2 crosses and 6 dots (or vice versa)

                      Correct charges on both ions
                                                                               

        2.       ‘Dot-and-cross’ diagrams can be used to predict the shape of covalent molecules.

              Fluorine has a covalent oxide called difluorine oxide, F₂O. The oxygen atom is covalently bonded to each fluorine atom.

                 (i)      Draw a ‘dot-and-cross’ diagram of a molecule of F₂O.  Show outer electron shells only.  [2]

                         Electron pairs in covalent bonds shown correctly using dots and crosses in a molecule of the F2O

                         Lone pairs correct on O and both F atoms

                 (ii)      Predict the bond angle in an F₂O molecule. Explain your answer.  [3] 

                       Bond angle 104.5°.   There are 2 bonded pairs and 2 lone pairs   Lone pairs repel more than bonded pairs

        3.       Chemists have developed models for bonding and structure which are used to explain different properties.

                  Ammonia, NH₃, is a covalent compound.

                  (i)      Explain what is meant by a covalent bond.  [1]   a shared pair of electrons

                 (ii)      Draw a ‘dot-and-cross’ diagram to show the bonding in NH₃.  Show outer electrons only.  [1]

                                                                                                           

                (iii)     Name the shape of the ammonia molecule and explain, why ammonia has this shape and has a bond angle of 107°.  [3] 

                     pyramidal   Explanation:  There are 3 bonded pairs and 1 lone pair   Lone pairs repel more than bonded pairs

        4.       Molecules of NCl₃ have a bond angle of 107°.

                  (i)      Name the shape of an NCl₃ molecule.  [1]   pyramidal

                 (ii)      Explain why a molecule of NCl₃ has this shape and a bond angle of 107°.  [3] 

                        electron pairs repel as far apart as possible

                        lone pairs repel more  

                        4 electron pairs surround central atom or diagram with 3 bonds and a lone pair

        5.       Antimony is in Group 5 of the Periodic Table. It forms a compound with hydrogen that has the formula SbH₃.

                 (i)      Predict the bond angle in SbH₃.  [1]  Bond angle 107°.  

                (ii)      Explain why a molecule of SbH₃ has this bond angle.  [2]

                        electron pairs repel electron pairs/bonds go as far apart as possible  lone pairs repel more

        6.       The ‘dot-and-cross’ diagram of an ammonia molecule is shown below.

                Predict, with reasons, the bond angle in an ammonia molecule.  [4]

                    NH3: 107°.   electron pairs repel other electron pairs  

                    lone pair has more repulsion   electron pairs get as far apart as possible