Presentation on theme: "Ionic and Covalent Bonding Electron and Lewis Dot Structures"— Presentation transcript:
1Ionic and Covalent Bonding Electron and Lewis Dot Structures James Hutchison
2Valence Electrons are…? The electrons responsible for the chemical properties of atoms, and are those in the outer energy level.Valence electrons - The s and p electrons in the outer energy levelthe 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 RuleIn Chapter 6, we learned that noble gases are unreactive in chemical reactionsIn 1916, Gilbert Lewis used this fact to explain why atoms form certain kinds of ions and moleculesThe 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)
16Stable Electron Configurations All atoms react to try and achieve a noble gas configuration.Noble gases have 2 s and 6 p electrons.8 valence electrons = already stable!This is the octet rule (8 in the outer level is particularly stable).Ar
17Ionic 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.
18Ionic CompoundsAlso called SALTSMade from: a CATION with an ANION (or literally from a metal combining with a nonmetal)
19Ionic 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.
20Ionic BondingNa+Cl -Note: Remember that NO DOTS are now shown for the cation!
21Ionic BondingLets do an example by combining calcium and phosphorus:CaPAll the electrons must be accounted for, and each atom will have a noble gas configuration (which is stable).
31= 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
32Properties 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
33NaCl 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
34Do 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)
35- 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.
36Metallic 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
37Sea of Electrons + Electrons are free to move through the solid. Metals conduct electricity.+
38Metals are MalleableHammered into shape (bend).Also ductile - drawn into wires.Both malleability and ductility explained in terms of the mobility of the valence electrons
39Due 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
43Ionic solids are brittle Strong Repulsion breaks a crystal apart, due to similar ions being next to each other.+-Force+-+-+-
44Covalent 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.
45Molecules 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)
46The nuclei repel each other, since they both have a positive charge (like charges repel). How does H2 form?(diatomic hydrogen molecule)++++
47How 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!++
48Covalent 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.
49Covalent bondingFluorine has seven valence electrons (but would like to have 8)F
50F F Covalent bonding Fluorine has seven valence electrons A second atom also has sevenFF
51F F Covalent bonding Fluorine has seven valence electrons A second atom also has sevenBy sharing electrons…FF
52F F Covalent bonding Fluorine has seven valence electrons A second atom also has sevenBy sharing electrons…FF
53F F Covalent bonding Fluorine has seven valence electrons A second atom also has sevenBy sharing electrons…FF
54F F Covalent bonding Fluorine has seven valence electrons A second atom also has sevenBy sharing electrons…FF
55F F Covalent bonding Fluorine has seven valence electrons A second atom also has sevenBy sharing electrons…FF
56F 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
57F F Covalent bonding Fluorine has seven valence electrons A second atom also has sevenBy sharing electrons……both end with full orbitalsFF8 Valence electrons
58F F Covalent bonding Fluorine has seven valence electrons A second atom also has sevenBy sharing electrons……both end with full orbitalsFF8 Valence electrons
59Molecular CompoundsCompounds that are bonded covalently (like in water, or carbon dioxide) are called molecular compoundsMolecular compounds tend to have relatively lower melting and boiling points than ionic compounds – this is not as strong a bond as ionic
60Molecular CompoundsThus, molecular compounds tend to be gases or liquids at room temperatureIonic compounds were solidsA molecular compound has a molecular formula:Shows how many atoms of each element a molecule contains
61Molecular 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).
62A 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
63H 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
64H O Water Put the pieces together The first hydrogen is happy The oxygen still needs one moreHO
65H O H Water So, a second hydrogen attaches Every atom has full energy levelsNote the two “unshared” pairs of electronsHOH
66Multiple 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?
67Dot diagram for Carbon dioxide CO2 - Carbon is central atom ( more metallic )Carbon has 4 valence electronsWants 4 moreOxygen has 6 valence electronsWants 2 moreCO
68Carbon dioxideAttaching 1 oxygen leaves the oxygen 1 short, and the carbon 3 shortCO
69Carbon dioxideAttaching the second oxygen leaves both of the oxygen 1 short, and the carbon 2 shortOCO
70Carbon dioxideThe only solution is to share moreOCO
71Carbon dioxideThe only solution is to share moreOCO
72Carbon dioxideThe only solution is to share moreOCO
73Carbon dioxideThe only solution is to share moreOCO
74Carbon dioxideThe only solution is to share moreOCO
75Carbon dioxideThe only solution is to share moreOCO
76O C O Carbon dioxide The only solution is to share more Requires two double bondsEach atom can count all the electrons in the bondOCO
77O 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
78O 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
79O 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
80How to draw them? Add up all the valence electrons. Count up the total number of electrons to make all atoms happy.Subtract; then Divide by 2Tells you how many bonds to drawFill in the rest of the valence electrons to fill atoms up.
81N H Example NH3, which is ammonia N – central atom; has 5 valence electrons, wants 8H - has 1 (x3) valence electrons, wants 2 (x3)NH3 has 5+3 = 8NH3 wants 8+6 = 14(14-8)/2= 3 bonds4 atoms with 3 bondsNH
82H H N H Examples Draw in the bonds; start with singles All 8 electrons are accounted forEverything is full – done with this one.HHNH
83Example: HCN HCN: C is central atom N - has 5 valence electrons, wants 8C - has 4 valence electrons, wants 8H - has 1 valence electron, wants 2HCN has = 10HCN wants = 18(18-10)/2= 4 bonds3 atoms with 4 bonds – this will require multiple bonds - not to H however
84H 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
85H 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
86H 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
87Another way of indicating bonds Often use a line to indicate a bondCalled a structural formulaEach line is 2 valence electronsHOHHOH=
89A 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
90C O Coordinate 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
91C O Coordinate 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
92Molecular Orbitals are... The model for covalent bonding assumes the orbitals are those of the individual atoms = atomic orbitalOrbitals that apply to the overall molecule, due to atomic orbital overlap are the molecular orbitalsA bonding orbital is a molecular orbital that can be occupied by two electrons of a covalent bond
93VSEPR: stands for... Valence Shell Electron Pair Repulsion Predicts the three dimensional shape of molecules.The name tells you the theory:Valence shell = outside electrons.Electron Pair repulsion = electron pairs try to get as far away as possible from each other.Can determine the angles of bonds.
94VSEPRBased on the number of pairs of valence electrons, both bonded and unbonded.Unbonded pair also called lone pair.CH4 - draw the structural formulaHas 4 + 4(1) = 8wants 8 + 4(2) = 16(16-8)/2 = 4 bonds
95VSEPR for methane (a gas): Single bonds fill all atoms.There are 4 pairs of electrons pushing away.The furthest they can get away is 109.5ºHHCHHThis 2-dimensional drawing does not show a true representation of the chemical arrangement.
96H C H H H 4 atoms bonded Basic shape is tetrahedral. A pyramid with a triangular base.Same shape for everything with 4 pairs.H109.5ºCHHH
97- Page 232Methane has an angle of 109.5o, called tetrahedralAmmonia has an angle of 107o, called pyramidalNote the unshared pair that is repulsion for other electrons.
98Bond Polarity Covalent bonding means shared electrons but, do they share equally?Electrons are pulled, as in a tug-of-war, between the atoms nucleiIn equal sharing (such as diatomic molecules), the bond that results is called a nonpolar covalent bond
99Bond PolarityWhen two different atoms bond covalently, there is an unequal sharingthe more electronegative atom will have a stronger attraction, and will acquire a slightly negative chargecalled a polar covalent bond, or simply polar bond.
100Electronegativity?The ability of an atom in a molecule to attract shared electrons to itself.Linus Pauling
101Table of Electronegativities Higher electronegativity
102Bond Polarity Refer to Handout Consider HCl H = electronegativity of 2.1Cl = electronegativity of 3.0the bond is polarthe chlorine acquires a slight negative charge, and the hydrogen a slight positive charge
103Bond Polarity d+ d- d+ and d- Only partial charges, much less than a true 1+ or 1- as in ionic bondWritten as:H Clthe positive and minus signs (with the lower case delta: ) denote partial charges.d+ d-d+ and d-
104Bond Polarity H Cl Can also be shown: the arrow points to the more electronegative atom.Table 8.3, p.238 shows how the electronegativity can also indicate the type of bond that tends to formH Cl
105Polar molecules Sample Problem 8.3, p.239 A polar bond tends to make the entire molecule “polar”areas of “difference”HCl has polar bonds, thus is a polar molecule.A molecule that has two poles is called dipole, like HCl
106Polar moleculesThe effect of polar bonds on the polarity of the entire molecule depends on the molecule shapecarbon dioxide has two polar bonds, and is linear = nonpolar molecule!
107Polar moleculesThe effect of polar bonds on the polarity of the entire molecule depends on the molecule shapewater has two polar bonds and a bent shape; the highly electronegative oxygen pulls the e- away from H = very polar!
108Polar moleculesWhen polar molecules are placed between oppositely charged plates, they tend to become oriented with respect to the positive and negative plates.
109Attractions between molecules They are what make solid and liquid molecular compounds possible.The weakest are called van der Waal’s forces - there are two kinds:#1. Dispersion forcesweakest of all, caused by motion of e-increases as # e- increaseshalogens start as gases; bromine is liquid; iodine is solid – all in Group 7A
110#2. Dipole interactionsOccurs when polar molecules are attracted to each other.2. Dipole interaction happens in waterFigure 8.25, page 240positive region of one molecule attracts the negative region of another molecule.
111#2. Dipole interactions H F d+ d- H F d+ d- Occur when polar molecules are attracted to each other.Slightly stronger than dispersion forces.Opposites attract, but not completely hooked like in ionic solids.H Fd+ d-H Fd+ d-
113#3. Hydrogen bonding…is the attractive force caused by hydrogen bonded to N, O, F, or ClN, O, F, and Cl are very electronegative, so this is a very strong dipole.And, the hydrogen shares with the lone pair in the molecule next to it.This is the strongest of the intermolecular forces.
114Order of Intermolecular attraction strengths Dispersion forces are the weakestA little stronger are the dipole interactionsThe strongest is the hydrogen bondingAll of these are weaker than ionic bonds
115#3. Hydrogen bonding defined: When a hydrogen atom is: a) covalently bonded to a highly electronegative atom, AND b) is also weakly bonded to an unshared electron pair of a nearby highly electronegative atom.The hydrogen is left very electron deficient (it only had 1 to start with!) thus it shares with something nearbyHydrogen is also the ONLY element with no shielding for its nucleus when involved in a covalent bond!
116Hydrogen Bonding (Shown in water) This hydrogen is bonded covalently to: 1) the highly negative oxygen, and 2) a nearby unshared pair.
117Hydrogen bonding allows H2O to be a liquid at room conditions.
118Attractions and properties Why are some chemicals gases, some liquids, some solids?Depends on the type of bonding!Network solids – solids in which all the atoms are covalently bonded to each other
119Attractions and properties Network solids melt at very high temperatures, or not at all (decomposes)Diamond does not really melt, but vaporizes to a gas at 3500 oC and beyondSiC, used in grinding, has a melting point of about 2700 oC
120Covalent Network Compounds Some covalently bonded substances DO NOT form discrete molecules.Diamond, a network of covalently bonded carbon atomsGraphite, a network of covalently bonded carbon atoms