Presentation on theme: "“Ionic, Covalent and Metallic Bonding”"— Presentation transcript:
1“Ionic, Covalent and Metallic Bonding” modified fromStephen L. Cotton
2Valence Electrons are…? electrons in the outer energy level.Responsible for properties of elementsValence electrons - The s and p electrons in the highest occupied energy levelCore electrons – are those in the energy levels below.
3Keeping Track of Electrons Atoms in the same column...Have the same outer electron configuration.Have the same valence electrons.The number of valence electrons are easily determined. It is the group number for a representative elementGroup 2A: Be, Mg, Ca, etc.have 2 valence electrons
4Electron Dot diagrams are… A way of showing & keeping track of valence electrons.How to write them?Write the symbol - it represents the nucleus and inner (core) electronsPut one dot for each valence electron (8 maximum)They don’t pair up until they have to (Hund’s rule)X
5The Electron Dot diagram for Nitrogen Nitrogen has 5 valence electrons to show.First we write the symbol.NThen add 1 electron at a time to each side.Now they are forced to pair up.We have now written the electron dot diagram for Nitrogen.
6The Octet RuleThe Octet Rule: in forming compounds, atoms tend to achieve a noble gas configuration; 8 in the outer level is stableEach noble gas (except He, which has 2) has 8 electrons in the outer level
7Formation of CationsMetals lose electrons to attain a noble gas configuration.They make positive ions (cations)If we look at the electron configuration, it makes sense to lose electrons:Na 1s22s22p63s1 1 valence electronNa1+ 1s22s22p6 This is a noble gas configuration with 8 electrons in the outer level.
8Electron Dots For Cations Metals will have few valence electrons (usually 3 or less); calcium has only 2 valence electronsCa
9Electron Dots For Cations Metals will have few valence electronsMetals will lose the valence electronsCa
10Electron Dots For Cations Metals will have few valence electronsMetals will lose the valence electronsForming positive ionsCa2+This is named the “calcium ion”.NO DOTS are now shown for the cation.
11Electron Dots For Cations Let’s do Scandium, #21The electron configuration is: 1s22s22p63s23p64s23d1Thus, it can lose 2e- (making it 2+), or lose 3e- (making 3+)Sc = Sc2+Sc= Sc3+Scandium (II) ionScandium (III) ion
12Electron Dots For Cations Let’s do Silver, element #47Predicted configuration is: 1s22s22p63s23p64s23d104p65s24d9Actual configuration is: 1s22s22p63s23p64s23d104p65s14d10Ag = Ag1+ (can’t lose any more, charges of 3+ or greater are uncommon)
13Electron Dots For Cations Silver did the best job it could, but it did not achieve a true Noble Gas configurationInstead, it is called a “pseudo-noble gas configuration”
14Electron Configurations: Anions Nonmetals gain electrons to attain noble gas configuration.They make negative ions (anions)S = 1s22s22p63s23p4 = 6 valence electronsS2- = 1s22s22p63s23p6 = noble gas configuration.Halide ions are ions from chlorine or other halogens that gain electrons
15Electron Dots For Anions Nonmetals will have many valence electrons (usually 5 or more)They will gain electrons to fill outer shell.3-P(This is called the “phosphide ion”, and should show dots)
16Bonds are…Forces that hold groups of atoms together and make them function as a unit. Two types:Ionic bonds – transfer of electrons (gained or lost; makes formula unit)Covalent bonds – sharing of electrons. The resulting particle is called a “molecule”
17Covalent BondsThe word covalent is a combination of the prefix co- (from Latin com, meaning “with” or “together”), and the verb valere, meaning “to be strong”.Two electrons shared together have the strength to hold two atoms together in a bond.
18Molecules 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 covalentlyCalled a “diatomic molecule” (O2)
19(diatomic hydrogen molecule) The nuclei repel each other, since they both have a positive charge (like charges repel).How does H2 form?(diatomic hydrogen molecule)++++
20How does H2 form? But, the nuclei are attracted to the electrons They share the electrons, and this is called a “covalent bond”, and involves only NONMETALS!++
21Covalent bonds Nonmetals hold on to their valence electrons. They can’t give away electrons to bond.But still want noble gas configuration.Get it by sharing valence electrons with each other = covalent bondingBy sharing, both atoms get to count the electrons toward a noble gas configuration.
22Covalent bondingFluorine has seven valence electrons (but would like to have 8)F
23F F Covalent bonding Fluorine has seven valence electrons A second atom also has sevenFF
24F F Covalent bonding Fluorine has seven valence electrons A second atom also has sevenBy sharing electrons…FF
25F F Covalent bonding Fluorine has seven valence electrons A second atom also has sevenBy sharing electrons…FF
26F F Covalent bonding Fluorine has seven valence electrons A second atom also has sevenBy sharing electrons…FF
27F F Covalent bonding Fluorine has seven valence electrons A second atom also has sevenBy sharing electrons…FF
28F F Covalent bonding Fluorine has seven valence electrons A second atom also has sevenBy sharing electrons…FF
29F F Covalent bonding …both end with full orbitals Fluorine has seven valence electronsA second atom also has sevenBy sharing electrons……both end with full orbitalsFF
30F F Covalent bonding Fluorine has seven valence electrons A second atom also has sevenBy sharing electrons……both end with full orbitalsFF8 Valence electrons
31F F Covalent bonding Fluorine has seven valence electrons A second atom also has sevenBy sharing electrons……both end with full orbitalsFF8 Valence electrons
33Molecular Compounds The formula for water is written as H2O The subscript “2” behind hydrogen means there are 2 atoms of hydrogen; if there is only one atom, the subscript 1 is omittedMolecular formulas do not tell any information about the structure (the arrangement of the various atoms).
34- Page 215These are some of the different ways to represent ammonia:3. The ball and stick model is the BEST, because it shows a 3-dimensional arrangement.1. The molecular formula shows how many atoms of each element are present2. The structural formula ALSO shows the arrangement of these atoms!
35A Single Covalent Bond is... A sharing of two valence electrons.Only nonmetals and hydrogen.Different from an ionic bond because they actually form molecules.Two specific atoms are joined.In an ionic solid, you can’t tell which atom the electrons moved from or to
36H O Water Each hydrogen has 1 valence electron - Each hydrogen wants 1 moreThe oxygen has 6 valence electrons- The oxygen wants 2 moreThey share to make each other completeHO
37H O Water Put the pieces together The first hydrogen is happy The oxygen still needs one moreHO
38H O H Water So, a second hydrogen attaches Every atom has full energy levelsNote the two “unshared” pairs of electronsHOH
39Multiple BondsSometimes atoms share more than one pair of valence electrons.A double bond is when atoms share two pairs of electrons (4 total)A triple bond is when atoms share three pairs of electrons (6 total)Table 8.1, p Know these 7 elements as diatomic:Br2 I2 N2 Cl2 H2 O2 F2What’s the deal with the oxygen dot diagram?
40Dot diagram for Carbon dioxide CO2 - Carbon is central atom ( more metallic )Carbon has 4 valence electronsWants 4 moreOxygen has 6 valence electronsWants 2 moreCO
41Carbon dioxideAttaching 1 oxygen leaves the oxygen 1 short, and the carbon 3 shortCO
42Carbon dioxideAttaching the second oxygen leaves both of the oxygen 1 short, and the carbon 2 shortOCO
43Carbon dioxideThe only solution is to share moreOCO
44Carbon dioxideThe only solution is to share moreOCO
45Carbon dioxideThe only solution is to share moreOCO
46Carbon dioxideThe only solution is to share moreOCO
47Carbon dioxideThe only solution is to share moreOCO
48Carbon dioxideThe only solution is to share moreOCO
49O C O Carbon dioxide The only solution is to share more Requires two double bondsEach atom can count all the electrons in the bondOCO
50O C O Carbon dioxide The only solution is to share more Requires two double bondsEach atom can count all the electrons in the bond8 valence electronsOCO
51O C O Carbon dioxide The only solution is to share more Requires two double bondsEach atom can count all the electrons in the bond8 valence electronsOCO
52O C O Carbon dioxide The only solution is to share more Requires two double bondsEach atom can count all the electrons in the bond8 valence electronsOCO
53H C N HCN Put single bond between each atom Need to add 2 more bonds Must go between C and N (Hydrogen is full)HCN
54H C N HCN Put in single bonds Needs 2 more bonds Must go between C and N, not the HUses 8 electrons – need 2 more to equal the 10 it hasHCN
55H C N HCN Put in single bonds Need 2 more bonds Must go between C and NUses 8 electrons - 2 more to addMust go on the N to fill its octetHCN
56A Coordinate Covalent Bond... When one atom donates both electrons in a covalent bond.Carbon monoxide (CO) is a good example:Both the carbon and oxygen give another single electron to shareOC
57Coordinate Covalent Bond When one atom donates both electrons in a covalent bond.Carbon monoxide (CO) is a good example: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.CO
58Coordinate Covalent Bond When one atom donates both electrons in a covalent bond.Carbon monoxide (CO)The coordinate covalent bond is shown with an arrow as:COC O
59Resonance is... When more than one valid dot diagram is possible. Consider the two ways to draw ozone (O3)Which one is it? Does it go back and forth?It is a hybrid of both, like a mule; and shown by a double-headed arrowfound in double-bond structures!
60Resonance in OzoneNote the different location of the double bondNeither 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.
61ResonanceOccurs 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.
62Polyatomic ions – note the different positions of the double bond. Resonance in a carbonate ion (CO32-):Resonance in an acetate ion (C2H3O21-):
63Ionic BondingAnions and cations are held together by opposite charges (+ and -)Ionic compounds are called salts.Simplest ratio of elements in an ionic compound is called the formula unit.The bond is formed through the transfer of electrons (lose and gain)Electrons are transferred to achieve noble gas configuration.
64Ionic CompoundsAlso called SALTSMade from: a CATION with an ANION (or literally from a metal combining with a nonmetal)
65Ionic BondingNaClThe 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.
66Ionic BondingNa+Cl -Note: Remember that NO DOTS are now shown for the cation!
78= Ca3P2 Ionic Bonding 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
79Properties of Ionic Compounds Crystalline solids - a regular repeating arrangement of ions in the solid: Fig. 7.9, page 197Ions are strongly bonded together.Structure is rigid.High melting pointsCoordination number- number of ions of opposite charge surrounding it
80NaCl CsCl TiO2 - Page 198 Coordination Numbers: Both the sodium and chlorine have 6NaClBoth the cesium and chlorine have 8CsClEach titanium has 6, and each oxygen has 3TiO2
81Do they Conduct?Conducting electricity means allowing charges to move.In a solid, the ions are locked in place.Ionic solids are insulators.When melted, the ions can move around.Melted ionic compounds conduct.NaCl: must get to about 800 ºC.Dissolved in water, they also conduct (free to move in aqueous solutions)
82- Page 198The ions are free to move when they are molten (or in aqueous solution), and thus they are able to conduct the electric current.
83Metallic Bonds are… How metal atoms are held together in the solid. Metals hold on to their valence electrons very weakly.Think of them as positive ions (cations) floating in a sea of electrons: Fig. 7.12, p.201
84Sea of Electrons + Electrons are free to move through the solid. Metals conduct electricity.+
85Metals are MalleableHammered into shape (bend).Also ductile - drawn into wires.Both malleability and ductility explained in terms of the mobility of the valence electrons
86Due to the mobility of the valence electrons, metals have: - Page 201Due to the mobility of the valence electrons, metals have:Notice that the ionic crystal breaks due to ion repulsion!1) Ductility2) Malleabilityand
90Ionic solids are brittle Strong Repulsion breaks a crystal apart, due to similar ions being next to each other.+-Force+-+-+-
91Crystalline structure of metal If made of one kind of atom, metals are among the simplest crystals; very compact & orderlyNote Fig. 7.14, p.202 for types:1. Body-centered cubic:every atom (except those on the surface) has 8 neighborsNa, K, Fe, Cr, W
92Crystalline structure of metal 2. Face-centered cubic:every atom has 12 neighborsCu, Ag, Au, Al, Pb3. Hexagonal close-packedevery atom also has 12 neighborsdifferent pattern due to hexagonalMg, Zn, Cd
93Alloys We use lots of metals every day, but few are pure metals Alloys are mixtures of 2 or more elements, at least 1 is a metalmade by melting a mixture of the ingredients, then coolingBrass: an alloy of Cu and ZnBronze: Cu and Sn
94Why use alloys? Properties are often superior to the pure element Sterling silver (92.5% Ag, 7.5% Cu) is harder and more durable than pure Ag, but still soft enough to make jewelry and tablewareSteels are very important alloyscorrosion resistant, ductility, hardness, toughness, cost
95More about Alloys… Table 7.3, p.203 – lists a few alloys Types? a) substitutional alloy- the atoms in the components are about the same sizeb) interstitial alloy- the atomic sizes quite different; smaller atoms fit into the spaces between larger“Amalgam”- dental use, contains Hg