1 Chapter 12 CHEMICAL BONDING Dr. Babar Ali

2 CHAPTER OUTLINE  The Modern Atom The Modern Atom  Electron Configuration of Atoms Electron Configuration of Atoms  Chemical Bond Chemical Bond  Ionic Bond Ionic Bond  Covalent Bond Covalent Bond  Polar & Non-polar Covalent Bonds Polar & Non-polar Covalent Bonds  Lewis Structures Lewis Structures

3 THE MODERN ATOM  The e - cloud consists of separate Energy levels, each containing a fixed # of e -  The ‘E’ levels  in ‘E’ based on their distance from the nucleus e - can move to higher E levels by absorbing energy such as heat or electricity Lower E Higher E Absorbs E Releases E When e - move to lower E-levels, they release E in the form of light

4 THE MODERN ATOM  The lowest ‘E’ level can only hold a maximum of 2 e -, while others can have 8, 18 and 32 e  The # of e - in the outermost filled energy level are called valence electrons

5 ELECTRON CONFIGURATON OF ATOMS  Similarities of behavior in the periodic table is due to the e - configuration of the atoms  Elements in a group have the same # of valence e -  similar e - configurations & properties  The # of valence e - for the main group elements is the same as their group number

6 CHEMICAL BOND  Most matter in nature is found in form of compounds --2 or more elements held together via chemical bonds  Elements combine together (bond) to fill their outer E-levels and achieve a stable structure (low E)  Noble gases are un-reactive since their E-levels are complete  The nature and type of the chemical bond is directly responsible for many physical and chemical properties of a substance: (e.g. melting point, conductivity)

7 CHEMICAL BOND  When a conductivity apparatus is placed in salt solution, the bulb will light  But when placed in sugar solution, the bulb does not light  This difference in conductivity between salt and sugar is due to the different types of bonds between their atoms.  Two common types of bonding are present: ionic & covalent

8 IONIC BOND  Ionic bonds occur when e - are transferred between 2 atoms  After bonding, each atom achieves a complete shell (noble gas configuration)

9 IONIC BOND  Ionic bonds occur between metals and non-metals.  Metals lose e - to form positive ions (cations)  Non-metals gain e - to form negative ions (anions)  The smallest particles of ionic compounds are ions (not atoms)

10 COVALENT BOND  Covalent bonds form when electrons are shared between 2 atoms  Covalent bonds form between two non-metals  The smallest particles of covalent compounds are molecules

11 COVALENT BOND  Covalent bonds are best represented with electron-dot or Lewis structures  Structures must satisfy octet rule (8 e - around each atom)  H is one exceptions, forming a doublet (2 e - )

12 COVALENT BOND  Bonding e - can be displayed by a dashed line  Non-bonding e - must be displayed as dots

13 POLAR & NON-POLAR BONDS  Two types of covalent bonds exist: polar and non-polar  Non-polar covalent bonds occur between similar atoms  In these bonds the e - pair is shared equally between the 2 p + Shared equally

14 POLAR & NON-POLAR BONDS  Polar covalent bonds occur between different atoms  In these bonds the e - pair is shared unequally between the 2 p +  As a result, there is a charge separation in the molecule, and partial charges on each atom Shared unequally

15 Examples: Identify each of the following substances as ionic, polar covalent or non-polar covalent: 1.PCl 3 2.MgF 2 3.O 2 4.SO 2 Polar covalent 2 Different non-metals Ionic Metal & non-metal Non-polar covalent Polar covalent 2 Different non-metals Same non- metals

16 LEWIS STRUCTURES  Lewis symbols for the first 3 periods of representative elements are shown below: 1 valence electron 2 valence electrons 7 valence electron 6 valence electron

17 LEWIS STRUCTURES  In a Lewis structure, a shared e - pair is indicated by two dots between the atoms, or by a dash connecting them.  Unshared pairs of valence electrons (called lone pairs) are shown as belonging to individual atoms or ions.

18 LEWIS STRUCTURES  Writing correct Lewis structures for covalent compounds requires an understanding of the # of bonds normally formed by common nonmetals # of bonds formed depends on the group number

19 LEWIS STRUCTURES  When an element has 2, 3, or 4 unpaired valence e -, its atoms sometimes share more than one of them with another atom. Thus double and triple bonds are possible. Triple bond Double bonds

20 EVALUATING LEWIS STRUCTURES  When evaluating Lewis structures, 2 items should be checked: 1.Structure contains the correct # of valence e - (Add valence e - for each atom) CO2CO (6) =16 2.Each atom should obey the Octet Rule (8 e - ) Hydrogen is an exception (doublet)

21 Example 1: Determine if each of the following Lewis structures are correct or incorrect. If incorrect, rewrite the correct structure 2(1) = 12 Octet is complete Doublets are complete Octet is incomplete Structure is incorrect

22 Example 2: Determine if each of the following Lewis structures are correct or incorrect. If incorrect, rewrite the correct structure. 2(5) + 4(1) = 14 Structure is incorrect Only 12 electrons shown Structure has 14 electrons Octets are complete Each N has 5 valance e -

23 SUMMARY Ionic Bond Metal & Non-metal Covalent Bond 2 Non-metals Non-polar Similar Atoms Polar Different Atoms

24 SUMMARY IonicCovalent Structural UnitIonsMolecules Melting PointHighLow Boiling PointHighLow Solubility in H 2 OHighLow or None Electrical Cond.HighNone ExamplesNaCl, AgBrH 2, H 2 O