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Ionic, Covalent and Metallic Bonding modified from Stephen L. Cotton.

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Presentation on theme: "Ionic, Covalent and Metallic Bonding modified from Stephen L. Cotton."— Presentation transcript:

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2 Ionic, Covalent and Metallic Bonding modified from Stephen L. Cotton

3 Valence Electrons are…? l electrons in the outer energy level. l Responsible for properties of elements l Valence electrons - The s and p electrons in the highest occupied energy level l Core electrons – are those in the energy levels below.

4 Keeping Track of Electrons l Atoms in the same column... 1)Have the same outer electron configuration. 2)Have the same valence electrons. l The number of valence electrons are easily determined. It is the group number for a representative element l Group 2A: Be, Mg, Ca, etc. – have 2 valence electrons

5 Electron Dot diagrams are… l A way of showing & keeping track of valence electrons. l How to write them? l Write the symbol - it represents the nucleus and inner (core) electrons l Put one dot for each valence electron (8 maximum) l They dont pair up until they have to (Hunds rule) X

6 The Electron Dot diagram for Nitrogen l Nitrogen has 5 valence electrons to show. l First we write the symbol. N l Then add 1 electron at a time to each side. l Now they are forced to pair up. l We have now written the electron dot diagram for Nitrogen.

7 The Octet Rule l The Octet Rule: in forming compounds, atoms tend to achieve a noble gas configuration; 8 in the outer level is stable l Each noble gas (except He, which has 2) has 8 electrons in the outer level

8 Formation of Cations l Metals lose electrons to attain a noble gas configuration. l They make positive ions (cations) l If we look at the electron configuration, it makes sense to lose electrons: l Na 1s 2 2s 2 2p 6 3s 1 1 valence electron l Na 1+ 1s 2 2s 2 2p 6 This is a noble gas configuration with 8 electrons in the outer level.

9 Electron Dots For Cations l Metals will have few valence electrons (usually 3 or less); calcium has only 2 valence electrons Ca

10 Electron Dots For Cations l Metals will have few valence electrons l Metals will lose the valence electrons Ca

11 Electron Dots For Cations l Metals will have few valence electrons l Metals will lose the valence electrons l Forming positive ions Ca 2+ NO DOTS are now shown for the cation. This is named the calcium ion.

12 Electron Dots For Cations l Lets do Scandium, #21 l The electron configuration is: 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 1 l Thus, it can lose 2e - (making it 2+), or lose 3e - (making 3+) Sc = Sc 2+ Scandium (II) ion Scandium (III) ion Sc = Sc 3+

13 Electron Dots For Cations l Lets do Silver, element #47 l Predicted configuration is: 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 5s 2 4d 9 l Actual configuration is: 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 5s 1 4d 10 Ag = Ag 1+ (cant lose any more, charges of 3+ or greater are uncommon)

14 Electron Dots For Cations l Silver did the best job it could, but it did not achieve a true Noble Gas configuration l Instead, it is called a pseudo-noble gas configuration

15 Electron Configurations: Anions l Nonmetals gain electrons to attain noble gas configuration. l They make negative ions (anions) l S = 1s 2 2s 2 2p 6 3s 2 3p 4 = 6 valence electrons l S 2- = 1s 2 2s 2 2p 6 3s 2 3p 6 = noble gas configuration. l Halide ions are ions from chlorine or other halogens that gain electrons

16 Electron Dots For Anions l Nonmetals will have many valence electrons (usually 5 or more) l They will gain electrons to fill outer shell. P 3- (This is called the phosphide ion, and should show dots)

17 16 Bonds are… Forces that hold groups of atoms together and make them function as a unit. Two types: 1) Ionic bonds – transfer of electrons (gained or lost; makes formula unit) 2) Covalent bonds – sharing of electrons. The resulting particle is called a molecule

18 17 Covalent Bonds l The word covalent is a combination of the prefix co- (from Latin com, meaning with or together), and the verb valere, meaning to be strong. l Two electrons shared together have the strength to hold two atoms together in a bond.

19 18 Molecules Many elements found in nature are in the form of molecules: a neutral group of atoms joined together by covalent bonds. For example, air contains oxygen molecules, consisting of two oxygen atoms joined covalently For example, air contains oxygen molecules, consisting of two oxygen atoms joined covalently Called a diatomic molecule (O 2 ) Called a diatomic molecule (O 2 )

20 19 How does H 2 form? l The nuclei repel each other, since they both have a positive charge (like charges repel). ++ (diatomic hydrogen molecule) + +

21 20 How does H 2 form? ++ l But, the nuclei are attracted to the electrons l They share the electrons, and this is called a covalent bond, and involves only NONMETALS!

22 21 Covalent bonds l Nonmetals hold on to their valence electrons. l They cant give away electrons to bond. –But still want noble gas configuration. l Get it by sharing valence electrons with each other = covalent bonding l By sharing, both atoms get to count the electrons toward a noble gas configuration.

23 22 Covalent bonding l Fluorine has seven valence electrons (but would like to have 8) F

24 23 Covalent bonding l Fluorine has seven valence electrons l A second atom also has seven FF

25 24 Covalent bonding l Fluorine has seven valence electrons l A second atom also has seven l By sharing electrons… FF

26 25 Covalent bonding l Fluorine has seven valence electrons l A second atom also has seven l By sharing electrons… FF

27 26 Covalent bonding l Fluorine has seven valence electrons l A second atom also has seven l By sharing electrons… FF

28 27 Covalent bonding l Fluorine has seven valence electrons l A second atom also has seven l By sharing electrons… FF

29 28 Covalent bonding l Fluorine has seven valence electrons l A second atom also has seven l By sharing electrons… FF

30 29 Covalent bonding l Fluorine has seven valence electrons l A second atom also has seven l By sharing electrons… l …both end with full orbitals FF

31 30 Covalent bonding l Fluorine has seven valence electrons l A second atom also has seven l By sharing electrons… l …both end with full orbitals FF 8 Valence electrons

32 31 Covalent bonding l Fluorine has seven valence electrons l A second atom also has seven l By sharing electrons… l …both end with full orbitals FF 8 Valence electrons

33 32

34 33 Molecular Compounds l The formula for water is written as H 2 O –The subscript 2 behind hydrogen means there are 2 atoms of hydrogen; if there is only one atom, the subscript 1 is omitted l Molecular formulas do not tell any information about the structure (the arrangement of the various atoms).

35 34 - Page 215 These are some of the different ways to represent ammonia: 1. The molecular formula shows how many atoms of each element are present 2. The structural formula ALSO shows the arrangement of these atoms! 3. The ball and stick model is the BEST, because it shows a 3-dimensional arrangement.

36 35 A Single Covalent Bond is... l A sharing of two valence electrons. l Only nonmetals and hydrogen. l Different from an ionic bond because they actually form molecules. l Two specific atoms are joined. l In an ionic solid, you cant tell which atom the electrons moved from or to

37 36 Water H O Each hydrogen has 1 valence electron - Each hydrogen wants 1 more The oxygen has 6 valence electrons - The oxygen wants 2 more They share to make each other complete

38 37 Water l Put the pieces together l The first hydrogen is happy l The oxygen still needs one more H O

39 38 Water l So, a second hydrogen attaches l Every atom has full energy levels H O H Note the twounshared pairs of electrons

40 39 Multiple Bonds l Sometimes atoms share more than one pair of valence electrons. l A double bond is when atoms share two pairs of electrons (4 total) l A triple bond is when atoms share three pairs of electrons (6 total) l Table 8.1, p Know these 7 elements as diatomic: Br 2 I 2 N 2 Cl 2 H 2 O 2 F 2 Whats the deal with the oxygen dot diagram?

41 40 Dot diagram for Carbon dioxide l CO 2 - Carbon is central atom ( more metallic ) l Carbon has 4 valence electrons l Wants 4 more l Oxygen has 6 valence electrons l Wants 2 more O C

42 41 Carbon dioxide l Attaching 1 oxygen leaves the oxygen 1 short, and the carbon 3 short O C

43 42 Carbon dioxide l Attaching the second oxygen leaves both of the oxygen 1 short, and the carbon 2 short O C O

44 43 Carbon dioxide l The only solution is to share more O C O

45 44 Carbon dioxide l The only solution is to share more O C O

46 45 Carbon dioxide l The only solution is to share more O CO

47 46 Carbon dioxide l The only solution is to share more O CO

48 47 Carbon dioxide l The only solution is to share more O CO

49 48 Carbon dioxide l The only solution is to share more O CO

50 49 Carbon dioxide l The only solution is to share more l Requires two double bonds l Each atom can count all the electrons in the bond O CO

51 50 Carbon dioxide l The only solution is to share more l Requires two double bonds l Each atom can count all the electrons in the bond O CO 8 valence electrons

52 51 Carbon dioxide l The only solution is to share more l Requires two double bonds l Each atom can count all the electrons in the bond O CO 8 valence electrons

53 52 Carbon dioxide l The only solution is to share more l Requires two double bonds l Each atom can count all the electrons in the bond O CO 8 valence electrons

54 53 HCN l Put single bond between each atom l Need to add 2 more bonds l Must go between C and N (Hydrogen is full) NHC

55 54 HCN l Put in single bonds l Needs 2 more bonds l Must go between C and N, not the H l Uses 8 electrons – need 2 more to equal the 10 it has NHC

56 55 HCN l Put in single bonds l Need 2 more bonds l Must go between C and N l Uses 8 electrons - 2 more to add l Must go on the N to fill its octet NHC

57 56 A Coordinate Covalent Bond... l When one atom donates both electrons in a covalent bond. l Carbon monoxide (CO) is a good example: OC Both the carbon and oxygen give another single electron to share

58 57 Coordinate Covalent Bond l When one atom donates both electrons in a covalent bond. l Carbon monoxide (CO) is a good example: OC Oxygen gives both of these electrons, since it has no more singles to share. This carbon electron moves to make a pair with the other single.

59 58 Coordinate Covalent Bond l When one atom donates both electrons in a covalent bond. l Carbon monoxide (CO) OC C O The coordinate covalent bond is shown with an arrow as:

60 59 Resonance is... l When more than one valid dot diagram is possible. l Consider the two ways to draw ozone (O 3 ) l Which one is it? Does it go back and forth? l It is a hybrid of both, like a mule; and shown by a double-headed arrow l found in double-bond structures!

61 60 Resonance in Ozone Neither structure is correct, it is actually a hybrid of the two. To show it, draw all varieties possible, and join them with a double-headed arrow. Note the different location of the double bond

62 61 Resonance Occurs when more than one valid Lewis structure can be written for a particular molecule (due to position of double bond) These are resonance structures of benzene. The actual structure is an average (or hybrid) of these structures.

63 62 Resonance in a carbonate ion (CO 3 2- ): Resonance in an acetate ion (C 2 H 3 O 2 1- ): Polyatomic ions – note the different positions of the double bond.

64 Ionic Bonding l Anions and cations are held together by opposite charges (+ and -) l Ionic compounds are called salts. l Simplest ratio of elements in an ionic compound is called the formula unit. l The bond is formed through the transfer of electrons (lose and gain) l Electrons are transferred to achieve noble gas configuration.

65 Ionic Compounds 1)Also called SALTS 2)Made from: a CATION with an ANION (or literally from a metal combining with a nonmetal)

66 Ionic Bonding NaCl The metal (sodium) tends to lose its one electron from the outer level. The nonmetal (chlorine) needs to gain one more to fill its outer level, and will accept the one electron that sodium is going to lose.

67 Ionic Bonding Na + Cl - Note: Remember that NO DOTS are now shown for the cation!

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69 Ionic Bonding l All the electrons must be accounted for, and each atom will have a noble gas configuration (which is stable). CaP Lets do an example by combining calcium and phosphorus:

70 Ionic Bonding CaP

71 Ionic Bonding Ca 2+ P

72 Ionic Bonding Ca 2+ P Ca

73 Ionic Bonding Ca 2+ P 3- Ca

74 Ionic Bonding Ca 2+ P 3- Ca P

75 Ionic Bonding Ca 2+ P 3- Ca 2+ P

76 Ionic Bonding Ca 2+ P 3- Ca 2+ P Ca

77 Ionic Bonding Ca 2+ P 3- Ca 2+ P Ca

78 Ionic Bonding Ca 2+ P 3- Ca 2+ P 3- Ca 2+

79 Ionic Bonding = Ca 3 P 2 Formula Unit This is a chemical formula, which shows the kinds and numbers of atoms in the smallest representative particle of the substance. For an ionic compound, the smallest representative particle is called a: Formula Unit

80 Properties of Ionic Compounds 1.Crystalline solids - a regular repeating arrangement of ions in the solid: Fig. 7.9, page 197 –Ions are strongly bonded together. –Structure is rigid. 2.High melting points l Coordination number- number of ions of opposite charge surrounding it

81 - Page 198 Coordination Numbers: Both the sodium and chlorine have 6 Both the cesium and chlorine have 8 Each titanium has 6, and each oxygen has 3 NaCl CsCl TiO 2

82 Do they Conduct? l Conducting electricity means allowing charges to move. l In a solid, the ions are locked in place. l Ionic solids are insulators. l When melted, the ions can move around. 3.Melted ionic compounds conduct. –NaCl: must get to about 800 ºC. –Dissolved in water, they also conduct (free to move in aqueous solutions)

83 - Page 198 The ions are free to move when they are molten (or in aqueous solution), and thus they are able to conduct the electric current.

84 Metallic Bonds are… l How metal atoms are held together in the solid. l Metals hold on to their valence electrons very weakly. l Think of them as positive ions (cations) floating in a sea of electrons: Fig. 7.12, p.201

85 Sea of Electrons l Electrons are free to move through the solid. l Metals conduct electricity.

86 Metals are Malleable l Hammered into shape (bend). l Also ductile - drawn into wires. l Both malleability and ductility explained in terms of the mobility of the valence electrons

87 - Page 201 1) Ductility2) Malleability Due to the mobility of the valence electrons, metals have: and Notice that the ionic crystal breaks due to ion repulsion!

88 Malleable Force

89 Malleable l Mobile electrons allow atoms to slide by, sort of like ball bearings in oil. Force

90 Ionic solids are brittle Force

91 Ionic solids are brittle l Strong Repulsion breaks a crystal apart, due to similar ions being next to each other. Force

92 Crystalline structure of metal l If made of one kind of atom, metals are among the simplest crystals; very compact & orderly l Note Fig. 7.14, p.202 for types: 1. Body-centered cubic: –every atom (except those on the surface) has 8 neighbors –Na, K, Fe, Cr, W

93 Crystalline structure of metal 2. Face-centered cubic: –every atom has 12 neighbors –Cu, Ag, Au, Al, Pb 3. Hexagonal close-packed –every atom also has 12 neighbors –different pattern due to hexagonal –Mg, Zn, Cd

94 Alloys l We use lots of metals every day, but few are pure metals l Alloys are mixtures of 2 or more elements, at least 1 is a metal l made by melting a mixture of the ingredients, then cooling l Brass: an alloy of Cu and Zn l Bronze: Cu and Sn

95 Why use alloys? l Properties are often superior to the pure element l Sterling silver (92.5% Ag, 7.5% Cu) is harder and more durable than pure Ag, but still soft enough to make jewelry and tableware l Steels are very important alloys –corrosion resistant, ductility, hardness, toughness, cost

96 More about Alloys… l Table 7.3, p.203 – lists a few alloys l Types? a) substitutional alloy- the atoms in the components are about the same size l b) interstitial alloy- the atomic sizes quite different; smaller atoms fit into the spaces between larger l Amalgam- dental use, contains Hg


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