Chemical bonds


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Ionic, Covalent and metallic bonds

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Chemical bonds

  1. 1. Chemical Bonding. Unions that build
  2. 2. <ul><li>Atoms tend to gain, lose or share electrons so as to have eight electrons in their outer electron shell giving them the same electronic configuration as a noble gas . </li></ul><ul><li>The rule is applicable to the main-group elements, especially carbon , nitrogen , oxygen , and the halogens , but also to metals such as sodium or magnesium . </li></ul><ul><li>In simple terms, molecules or ions tend to be most stable when the outermost electron shells of their constituent atoms contain eight electrons. </li></ul>
  3. 3. <ul><li>The octet rule does not work for predicting the charges on transition metals ions. </li></ul><ul><li>Transition metals are located on the periodic table in the ten columns between columns for the representative elements, and the groups are labeled IB to VIIIB. </li></ul><ul><li>The transition metals typically produce ions with 1 +, 2+, 3+ and sometime 4+ charges, and unlike the representative elements many transition metals can have more than one charge state </li></ul>
  4. 4. <ul><li>Valence electrons : Electrons in the outermost electron shells, maximum 8 electrons. noble gases has 8 electrons </li></ul><ul><li>Ion : A charged atom. Can be either positive or negative. </li></ul><ul><ul><li>Positive ion : Is an atom that lost at least one electron, are called cations . Example Na + , Mg 2+ , Al 3+ </li></ul></ul><ul><ul><li>Negative ion : Is an atom that gained at least one electron, are called anions . Cl - , O 2- , N 3- </li></ul></ul>
  5. 5. <ul><li>Groups IA, IIA, and IIIA have metallic atoms that tend to lose electrons to acquire electronic configuration of a noble gas forming positive ions . </li></ul><ul><li>Groups VA, VIA, VIIA have non metallic atoms that tend to gain electrons to acquire electronic configuration of a noble gas forming negative ions . </li></ul>
  6. 6. Element Group Valence e - Electrons to form Ion Ion Formed Lost Gained Sodium IA Na + Magnesium IIA Mg 2+ Calcium IIA Ca 2+ Aluminum IIIA Al 3+ Sulfur VIA S 2- Oxygen VIA O 2- Chlorine VIIA Cl - Bromine VIIA Br -
  7. 7. <ul><li>Lewis structures , also called Lewis-dot diagrams , Electron-dot diagrams or Electron-dot structures , are diagrams that show the bonding between atoms of a molecule, and the lone pairs of electrons that may exist in the molecule. </li></ul><ul><li>Consists of the element symbol surrounded by &quot;dots&quot; to represent the number of electrons in the outer energy level (correlated by the Group number). </li></ul>
  8. 9. However, because of the high charge that would result, either C 4+ or C 4- for carbon and Si 4+ or Si 4- for silicon
  9. 10. <ul><li>Lithium </li></ul><ul><li>Calcium </li></ul><ul><li>Aluminum </li></ul><ul><li>Carbon </li></ul><ul><li>Nitrogen </li></ul><ul><li>Oxygen </li></ul><ul><li>Chlorine </li></ul><ul><li>Argon </li></ul><ul><li>Lithium ion </li></ul><ul><li>Calcium ion </li></ul><ul><li>Aluminum ion </li></ul><ul><li>Carbon </li></ul><ul><li>Nitrogen ion </li></ul><ul><li>Oxygen ion </li></ul><ul><li>Chlorine ion </li></ul><ul><li>Argon </li></ul>
  10. 11. Symbol Atomic Electronic configuration Lewis atom structure Formed ion Ionic Electronic configuration Lewis ionic structure Li 1s 2 2s 1 Li  Li + 1s 2 Li + Be B C N O F Ne
  11. 12. <ul><li>A chemical bond is the attraction caused by the electromagnetic force between opposing charges, either between electrons and nuclei or as the result of a dipole attraction. </li></ul><ul><li>The strength of bonds varies considerably; there are &quot;strong bonds&quot; such as covalent or ionic bonds and &quot;weak bonds&quot; such as dipole-dipole interactions , the London dispersion force and hydrogen bonding . </li></ul>
  12. 13. <ul><li>Type of chemical bond that involves a metal and a nonmetal ion through electrostatic attraction. It is a bond formed by the attraction between two oppositely charged ions, The electrostatic attraction between the oppositely charged ions causes them to come together and form a bond like magnets . </li></ul><ul><li>The metal donates one or more electrons , forming a positively charged ion or cation with a stable electron configuration . These electrons then enter the non metal, causing it to form a negatively charged ion or anion which also has a stable electron configuration. </li></ul>
  13. 14. For example, common salt is sodium chloride. When sodium (Na) and chlorine (Cl) are combined, the sodium atoms each lose an electron forming a cation (Na + ), and the chlorine atom gain an electron to form an anion (Cl − ). Na + Cl  Na + + Cl -
  14. 15. <ul><li>Formed between a metallic element and a non metallic element. </li></ul><ul><li>The bonding involves electrons transfer , the metal atom donates electrons while the non metal accept the electrons. </li></ul><ul><li>The compounds formed are solids with a crystal lattice tridimensional structure. </li></ul><ul><li>Most of them dissolve in water giving solutions that conducts electricity </li></ul><ul><li>Salts (NaCl) and acids (HCl) are ionic compounds </li></ul>
  15. 16. <ul><li>1. Find the total number of electrons: For each atom, read the group number. 2. Draw a first tentative structure: The element with the least number of atoms is usually the central element. Draw a tentative molecular and electron arrangement attaching other atoms with single bonds as the first guess. </li></ul><ul><li>3. Add electrons as dots to get octets around atoms: When counting electrons for the octet around an atom, count both electrons in a bond for each atom and any lone pair electrons. Hydrogen, of course, gets only 2 electrons. 4. Count the total number of electrons in the final structure to see if the total agrees with the number tabulated in step #1. If not, then move a lone pair of electrons into a double bond. Or add more lone pairs of electrons. </li></ul><ul><li>5. Cycle through steps 3 and 4 several times until you get it right by trial and error. </li></ul>
  16. 17. <ul><li>Na Cl Na IA = 1e Cl VIIA= 7e </li></ul><ul><li>Na  +  Na + </li></ul><ul><li>Mg Cl 2 Mg IIA=2e Cl VIIA= 7e </li></ul><ul><li> Mg  +  Mg 2+ </li></ul><ul><li>RbBr </li></ul><ul><li>CaBr 2 </li></ul><ul><li>AlF 3 </li></ul><ul><li>SrO </li></ul>    Cl        Cl -         Cl        Cl        Cl -         Cl -    
  17. 18. <ul><li>Chemical bonding is characterized by the sharing of pairs of electrons between atoms. </li></ul><ul><li>Is formed by at least two non-metallic elements, they can be molecules of the same atom like O 2 or different atoms like H 2 O. </li></ul><ul><li>The atoms can share more than one pair of electrons, they can share two or even three pair of electrons, like single, double or triple bonds. </li></ul>
  18. 19. The pair of shared electrons can be drawn with lines Chlorine molecule Cl 2 Cl = 7 e pair of shared electrons in red, each chlorine atom has 8 e or     Cl        Cl   
  19. 20. <ul><li>Single: One pair of electrons are shared. </li></ul><ul><li>Double: Two pairs of electrons are shared. </li></ul><ul><li>Triple: Three pairs of electrons are shared </li></ul>or
  20. 21. <ul><li>Write the valence electrons of the Nitrogen atom </li></ul><ul><li>Write the total number of electrons from both atoms </li></ul><ul><li>Draw the dot diagram </li></ul><ul><li>Arrange the electrons using octet rule (both atoms must have 8 electrons how many electrons must they share?) </li></ul>
  21. 22. <ul><li>N from family VA= 5 electrons </li></ul><ul><li>For the molecule N 2 are 10 electrons </li></ul><ul><li>Sharing just one pair doesn’t apply the octet rule. </li></ul><ul><li> </li></ul><ul><li>Neither sharing two pairs of electrons apply </li></ul><ul><li>But sharing THREE pair of electrons the octet rule does apply </li></ul><ul><li>or N N </li></ul>       N      N      N      N      N      N     N     N    
  22. 23. <ul><li>F 2 </li></ul><ul><li>NH 3 </li></ul><ul><li>H 2 </li></ul><ul><li>H 2 S </li></ul><ul><li>HBr </li></ul><ul><li>CH 4 </li></ul><ul><li>CO 2 </li></ul><ul><li>CO </li></ul><ul><li>O 2 </li></ul><ul><li>CCl 4 </li></ul>
  23. 24. <ul><li>Polar covalent: between atoms of different elements. Example H 2 O, H 2 S, CO 2 , CCl 4. The type of bond is also determined by the difference of the electronegativity values of the elements <(below)1.7 </li></ul><ul><li>Example : H 2 O </li></ul><ul><li>H=2.1 O=3.5  3.5-2.1= 1.4 polar covalent bond </li></ul><ul><li>Non-polar Covalent: Between molecules. Same elements. Example H 2 , O 2 , Cl 2 , F 2 . The type of bond is also determined by the difference of the electronegativity values of the elements = 0 </li></ul><ul><li>Example F 2 </li></ul><ul><li>F= 4  4-4 = 0 Non-polar Covalent bond </li></ul>
  24. 25. Compound Electronegativity value of each atom Electronegativity difference Type of bond F 2 F: 4.0 F: 4.0 4.0 – 4.0 = 0 Covalent Non-polar H 2 S NaF RbBr NH 3 HF MgO KCl N 2 CH 4
  25. 27. <ul><li>In chemistry , polarity refers to a separation of electric charge leading to a molecule having an electric dipole . </li></ul><ul><li>Polar: Is a molecule that can dissolve in water like Salts (NaCl, KF, etc) and Acids (HCl, HNO 3 , etc). </li></ul><ul><li>Non polar: Is a molecule that can not dissolve in water like fats, oils, gasoline, methane gas (CH 4 ) carbon tetrachloride (CCl 4 ), CO 2 . </li></ul>
  26. 28. <ul><li>A water molecule , a commonly-used example of polarity. The two charges are present with a negative charge in the middle (red shade), and a positive charge at the ends (blue shade). </li></ul>
  27. 30. <ul><li>Metallic bonding is the electromagnetic interaction between delocalized electrons , called &quot;electrons sea“. </li></ul><ul><li>The electrons sea are the responsible for the physical properties of solid metals: conduct heat and electricity, generally high melting and boiling points,strong, malleable (can be hammered or pressed out of shape without breaking), ductile (able to be drawn into a wire), metallic lustre </li></ul><ul><li>The elements involved in this type of bonding are mainly the transition metals like Fe, Cu, Au, Ag, Al, Zn, Pt, etc. </li></ul>
  28. 33. <ul><li>Are the forces holding molecules together </li></ul><ul><ul><li>Dipole-dipole forces </li></ul></ul><ul><ul><li>Weak London dispersion or van der Waal's force . </li></ul></ul><ul><ul><li>Hydrogen bond Certain substances such as H 2 O, HF, NH 3 form hydrogen bonds, and the formation of which affects properties (solubility) of substance. Other compounds containing OH and NH 2 groups also form hydrogen bonds. Molecules of many organic compounds such as alcohols, acids, amines, and aminoacids contain these groups, and thus hydrogen bonding plays a important role in biological science. </li></ul></ul>
  29. 34. <ul><li>Which of the following pairs has the strongest hydrogen bond. </li></ul><ul><li>HCl or HF </li></ul><ul><li>NH 3 or PH 3 </li></ul><ul><li>H 2 O or H 2 S </li></ul>