Chemistry 11 Lewis Structures Study Guide. After discussing about ionic and covalent bonds, there are times when it is valuable to draw

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1 Chemistry 11 Lewis Structures Study Guide After discussing about ionic and covalent bonds, there are times when it is valuable to draw Lewis structure ( electron dot diagrams ) to visualize how valence electrons are distributed in an atom, ion or molecule These structures will also allow us to determine the of certain molecules in solution which we will learn later in the course! polarity Lewis Structures of Simple Ionic Compounds To draw the Lewis Structure for ionic compounds: 1 Determine the charge expected for each atom in the compound 2 Arrange the nonmetal atoms symmetrically around the metal atom 3 Fill in the valence electrons for each atom 4 Remove the electrons from the outer shell of the metal atom to form the ion 5 Distribute the electrons equally to each nonmetal atom to form the ion 2T I Example: Draw the Lewis Structure of MgCl 2 tee, Mg has 2 valence e ; will form It ion Cl has 7 valence e ; will form I ion gain : Cl Mg : ~ Cl L : :c! : as Este It Ēmg ] Lewis Structures of Covalent Compounds that Obey the Octet Rule f : :c! :] " The octet rule states that most atoms (except hydrogen) tend to have 8 electrons in its outer shell as a result of forming covalent bonds To draw the Lewis Structure for covalent compounds: 1 Count only if the covalent compound is charged ) NOI 5042, eg up the total number of valence electrons for each atom in the molecule ( 2 ) Adjust the total number by subtracting one electron for every positive charge, and adding one electron for every negative charge on the molecule (if applicable) 3 Determine which atoms are bonded together and show this bond by drawing a line connecting the two atoms This bond reflects 2 electrons 4 Subtract the number of bonding electrons from the total number of valence electrons 5 Place the remaining valence electrons on the terminal atoms first to complete the octet 6 Place all left over electrons around the central atom if necessary * 7 If a central atom has less than an octet of electrons, have a neighbour share electrons with the deficient atom by putting extra pairs of electrons into the bond (ie Double and Triple bonds) Ionic If bonds

2 C N Oo covalent compound Example: Draw the Lewis Structure for C 4 (C is the central atom!) group 14 C has valence e Each has valence e Central Atom e I 8 be O C 8 total e 8 bonding e 0 e left! r Check for octet V I except for hydrogen Terminal Atom Example: Draw the Lewis Structure for NO A 2 (N is the central atom!) [ : N has valence e 5 e 5 Each O has valence e Ix 5Ve 5 re 12 e Add e 6 for negative charge t2ye? 1 e } 1 18 e total [ :] O N O ] 18 ve be 14 ve 18 total e 4 bonding e 14 e left! If O 14 Ve ve 2 ve 1Charg1 Place remaining e 2 ve Ve O around O first Then place left over e around N 0 [ O N O ] Notice that N only has 6 e around it ave one of ii the O donate an extra pair of e to the bond to form a double bond! an:[ 0 es on [ O N O ] [ O N O ] [ :p no? Structure Depending on the oxygen you chose to donate an extra pair, you would have drawn a different structure These interchangeable structures are known as resonance structures Exceptions to the Octet Rule ve group 15 I line 4 2 bonding LIVE Certain atoms don't possess a full octet of electrons after covalent bonding can only have 2 electrons in its outer shell Other atoms such as Be (4 electrons), B and At (6 electrons) can only share a certain number of electrons due to the fact that they have low They are unable to pull extra electrons on a nearby atom into the covalent electronegativity bonds 8 Ve 8 be 2 6 covaient compound WI ve :[

3 expanded } } A molecule in which one or more atoms (except hydrogen) don t possess a full octet of electrons is called an e deficient molecule Example: Draw the Lewis Structure for BF 3 (B is the central atom!) grp 13 B has valence e 3 e Each F has valence e 21 e " e deficient ve " 3 7 ve 24ve 24 e total 3ve awe 24Ve o Bl F B F Fo Note that B only has 6 e around it No attempt is made to donate extra electron pairs to the bonds F, a / \ a : OF GF Some elements in the 3rd and of the periodic table may have valence e 4th more than 8 in the outer shell after covalent bonding This is due to the fact that the extra electrons can fit in the d orbital of these atoms Atoms that are able to have more than 8 electrons have an expanded octet Example: Draw the Lewis Structure for PCl 5 (P is the central atom!) Gbe Move l8vei8veo O 9, P has valence e 5 e ve 5Ve Each Cl has valence e 35 e 40 Ve " e Ve 3 sue total : Kove lobe 3 Ore Cl Cl socii I o o \ / ve Cl : Cl P Cl Note that P has 10 e around it No attempt is made to alter this arrangement Cl 9oci 4 :c?! D p octet

4 Strength of ionic bond: 1 The smaller the size of the ions, the stronger the ionic bond strength 2 The larger the charge on the ion, the stronger the ionic bond strength Strength of covalent bond: 1 The smaller the size of the atoms, the stronger the covalent bond strength 2 Triple > Double > Single (strength and length wise) Don't core notation use EN found in the handbook / and end Of class

5 Don't core notation use EN found in the handbook / and end Of class