A. The Basics

1. Chapter 1: Chemical Bonding 1.1 Forming and Representing Compounds A. The Basics • scientists have studied the way in order to elements and compounds appear in nature chemical bonding categorize most are combined with in nature (called ) and are  metals non-metals ores solids

2. a few are found in their metals pure form  …precious metals Hg metals (except ) in pure form are  solids

3. combine with one another to form non-metals  solids, liquids or gases never the only elements that are found in in nature are the  combined form noble gases

4. atoms in such a way that they create a gain, lose or share electrons full outer energy level… called the octet rule • the can only hold and therefore satisfies the octet rule when it has first energy level two e two e in it • octet rule is a …not all elements follow it at all times guideline

5. are the electrons in the valence e outermost energy level of an atom • they are theonly electrons involved in chemical bonding • for representative elements () group number (ignore the “1” in front of groups above 10) tells youthe number of groups 1,2 and 13-18 valence electrons • period number tells youthe number of energy levels occupied by electrons

6. transition metals • for many , the number of valence electrons is not as predictable…it depends on the environment around the ion eg) iron can be Fe3+ or Fe2+ number of valence e ion charge • the can be used to determine eg) Fe3+ had 3 valence electrons

7. B. Electron Dot Diagrams • you can’t see atoms and electrons, therefore it is convenient toto show the structure and formation of draw models chemical bonds electron dot diagram • an is one such model • consists of the with symbol for the element dots representing the valence e • when drawing the diagrams, look up the , then place number of valence e dots around the symbol clockwise for a maximum of four dots

8. if you have more electrons to place,go back to the top of the symbol and start pairing up the e     Si Na Ca Al               Ar    O Cl      P          

9. full • a orbital is called a and is (at this level) lone pair not involved in bonding • a orbital contains a bonding electron half full   lone pairs   O   bonding e bonding capacity • the of an atom is the maximum number ofthat it can form(equals the number of ) single covalent bonds bonding e

10. Try These Draw the Lewis diagram (electron dot diagram) for each of the following: H C Mg P He F K Be S Br

11. C. Ionic Bonding • an is the electrostatic attraction between oppositely charged ions ionic bond metals three or fewer valence e • most have • they tend to these electrons and become lose positive ions (cations) + Na Na Crash course Lewis dot diagram

12. more than four valence e • most have non-metals • they tend to and become gain electrons negative ions (anions) 2- O O

13. after ions form, the attraction between the positive charge and negative charge draws the ions together, forming an ionic bond • when drawing the electron dot diagrams for ionic compounds: the number ofelectrons by themustthe number of electrons by the lost metal equal gained non-metal the on the compound must be net charge zero you may have to have of theto balance out the more than one metal and/or non-metal charges

14. Mg O Examples Na Cl NaCl MgO

15. Examples F Ca F CaF2 K S K K2S

16. Fe Fe N N Mg Mg Mg O O O Fe2O3 Mg3N2

17. notice the following about the diagrams: no valence electrons • the metal has(since theythem) • the non-metal has thevalence level • both ions haveand the • charges =charges lose filled square brackets charge positive negative

18. D. Covalent Bonding • a is formed when two non-metals share a pair of electrons covalent bond covalent bonds • compounds containing are called molecular compounds ions are not formed!!! • electron dot diagrams used to show molecular compounds are called Lewis structures Covalent Bond video

19. instead of transferring electrons, valence electrons are now to satisfy the shared octet rule • the electrons that are shared are called a bonding pair • sharing two or three pairs of electrons between two atoms results in a double or triple bond, respectively

20. to draw the structures: • place the atom with thein the most bonding electrons centre • arrange all other atoms around it as as possible symmetrically • to make sure that all atoms have the(remember that hydrogen only needselectrons to be satisfied) share electrons octet rule satisfied two Covalent bonding video

21. H H P H H H P H eg) PH3

22. Try These Draw the Lewis diagram (electron dot diagram) for each of the following: 1. HCl 4. NBr3 2. CH4 5. C2H4 3. F2 6. N2

23. Br N Br Br F F N N H Cl H H H C H H C C H H H

24. H P H H P H H H E. Structural Formulas • a is another way of drawing molecules structural formula (diagram) • to draw them, figure out the Lewis structure then replace all shared pairs of e with a line and leave off the lone pairs eg) PH3 Lewis Diagram Structural Diagram

25. Try These Draw the structural formula for each of the following: 1. HCl 4. NBr3 2. CH4 5. C2H4 3. F2 6. N2

26. Br N Br H Cl Br H H H H H C C C H H H F F N N

27. F. Metallic Bonding • most metals are at room temperature which means that there must be solids strong attractive forces holding the atoms of a pure metal together • metals form orwith ionic bonds DO NOT covalent other metal atoms • in all the atoms share all the valence e metallic bonding • the valence electrons are , which means they are from one atom to another delocalized free to move

28. metallic bonds are made up of a network of positive metal ions in a “sea” of electrons • a is the metallic bond electrostatic force of attraction between the positive metal ions and the negative sea of electrons • this theory helps explain the of metals properties eg) good conductors of electricity and heat, ductility, malleability

29. Metallic Bond Model metal cations “sea” of delocalized electrons

30. 1.2 The Nature of Chemical Bonds A. Electronegativity • the of an element is therelative measure of the ability of an atom to electronegativity attract electrons in a chemical bond • there is an attraction between theof an atom and the nucleus (protons) valence ein an adjacent atom nucleus electrons

31. each element is designated a number to represent how strong it’s nucleus is at attracting another atom’s valence e

32. higher • electronegativity means greater attraction (affinity) • trend on periodic table – electronegativity and increases across period decreases down group • since do not readily react with other substances, electronegativities have been assigned to them noble gases not • understanding electronegativity has contributed to the knowledge of bonding in ionic and molecular compounds

33. Electronegativity and the Periodic Table decreases increases

34. B. Size & Electronegativity • as you move from left to right across a period, both the and electronegativity, atomic number increase however size of the atom decreases

35. here is why size decreases across a period: • the size of an atom depends on theof thecontaining the radius energy level valence e • in any given period, the valence e of each atom occupy the same energy level • as you move across the period, the and thus the in the nucleus atomic number increases number of protons increases • there is a between the andwhen there are more , therefore the atom is greater amount of attraction nucleus e protons smaller

36. Period 2 Elements 3 p+ 6 p+ 9 p+ 1 valence e 4 valence e 7 valence e Li C F

37. so, the next question is “why does electronegativity increase when atomic size across a period decreases?” • the strength of the attraction (and therefore electronegativity) between oppositely charged particles depends on two factors: distance • thebetween the charges – the attractive force between opposite charges with thebetween them decreases square of the distance • theof the charges – the attractive force isto the magnitude directly proportional amount of charge

38. this means that an atom that isand has lots of(like fluorine)will have aamount of electrostatic attraction (electronegativity) for the of another atom small protons very large e • big atoms have but they are by the therefore have a amount of attraction(electronegativity) for the of another atom lots of protons inner levels of e shielded small e

39. Cs F Si Si   distance between nucleus of cesium and valence electrons of silicon distance between nucleus of fluorine and valence electrons of silicon nucleus of cesium nucleus of fluorine valence electrons of silicon valence electrons of silicon

40. C. Bond Type & Electronegativity • electronegativities can be related to bond types: • ionic bonds occur between metals and non-metals • metals have electronegativitiesand will while non-metals have and will low lose e high electronegativities gain e attract each other • the two ions that are formed will and form a chemical bond

41. non-metallic atoms • covalent bonds occurs between • if you look at two atoms that have the electronegativity, like in H2(g),the two nuclei of the atoms will attract the same electrons with exactly the same strength • the electrons are shared equally between the two atoms

42. when two non-metals that have electronegativities share electrons, the sharing is different no longer equal higher • the element with the electronegativity pulls the e closer to itself

43. this results in one end of the bond having aand the other end of the bond having a () slightly negative charge slightly positive charge (+) +  • bonds that have arecalled unequal sharing of electrons polar covalent bonds • also called since the bonds have bond dipoles oppositely charged ends

44. Bond Dipole Arrows “arrow” points towards element with higher electronegativity (-) “+” at the end that is + H – F + -

45. Try These: Draw the bond dipole arrow, label the + and  ends, and state the bond type (polar, nonpolar, ionic) 0.4 + - 6. C – H polar 1. H – H nonpolar 0.8 7. Cl – Cl - + nonpolar 2. N – H polar 1.3 2.0 + - 8. Si – Cl - + polar 3. B – F polar 0.8 1.2 + - - + 4. S – O 9. O – H polar polar 5. P – H 10. Na – Cl nonpolar ionic

46. you can use the difference in electronegativity between two atoms to determine bond character Difference in Electronegativity 3.3 1.7 0.5 0 slightly polar covalent mostly ionic polar covalent non-polar covalent

47. bond classification is not simple • as you can see, • bonding is considered a and there is continuum no clear distinction between ionic and covalent bonding

48. Chapter 2: Chemical Bonding 2.1 Three Dimensional Structures A. Ionic Crystals • ionic compounds have crystal structure oppositely charged ions • they form so that are asas possible close together • this is called a 3-D array of alternating positive and negative ions crystal lattice

49. since all the in the lattice are the attractive forces molecules… same, you cannot call them all each positive ion is attracted to of the negative ions around it (and vice versa) • the chemical formula is the lowest whole number ratio for that type of crystal eg) NaCl has a 1:1 ratio of Na ions to Cl ions sodium chloride

50. there are many different and they all depend on the way the ions crystal shapes pack together • shape also depends on the relative size of the ions and the charges on the ions