Chapter 9 Chemical Bonding I: Lewis Theory Chemistry: A Molecular Approach, 1st Ed. Nivaldo Tro Chapter 9 Chemical Bonding I: Lewis Theory

Bonding Theories explain how and why atoms attach together explain why some combinations of atoms are stable and others are not why is water H2O, not HO or H3O one of the simplest bonding theories was developed by G.N. Lewis and is called Lewis Theory Lewis Theory emphasizes valence electrons to explain bonding using Lewis Theory, we can draw models – called Lewis structures – that allow us to predict many properties of molecules aka Electron Dot Structures such as molecular shape, size, polarity Tro, Chemistry: A Molecular Approach

TO LOWER THE POTENTIAL ENERGY Why Do Atoms Bond? TO LOWER THE POTENTIAL ENERGY Tro, Chemistry: A Molecular Approach

Potential Energy Between Charged Particles The repulsion between like-charged particles increases as the particles get closer together. To bring them closer requires the addition of more energy. The attraction between opposite-charged particles increases as the particles get closer together. Bringing them closer lowers the potential energy of the system. Tro, Chemistry: A Molecular Approach

Bonding a chemical bond forms when the potential energy of the bonded atoms is less than the potential energy of the separate atoms have to consider following interactions: nucleus-to-nucleus repulsion electron-to-electron repulsion nucleus-to-electron attraction Tro, Chemistry: A Molecular Approach

Types of Bonds Types of Atoms Type of Bond Bond Characteristic metals to nonmetals Ionic electrons transferred nonmetals to Covalent shared metal to metal Metallic pooled Tro, Chemistry: A Molecular Approach

Types of Bonding

Ionic Bonds when metals bond to nonmetals, some electrons from the metal atoms are transferred to the nonmetal atoms metals have low ionization energy, relatively easy to remove an electron from nonmetals have high electron affinities, relatively good to add electrons to Tro, Chemistry: A Molecular Approach

Determining the Number of Valence Electrons in an Atom Can be determined from the electron configuration. Tro, Chemistry: A Molecular Approach

Determining the Number of Valence Electrons in an Atom the column number on the Periodic Table will tell you how many valence electrons a main group atom has Transition Elements all have 2 valence electrons; Why? 1A 2A 3A 4A 5A 6A 7A 8A Li Be B C N O F Ne 1 e-1 2 e-1 3 e-1 4 e-1 5 e-1 6 e-1 7 e-1 8 e-1 Tro, Chemistry: A Molecular Approach

Lewis Symbols of Atoms aka electron dot symbols use symbol of element to represent nucleus and inner electrons use dots around the symbol to represent valence electrons pair first two electrons for the s orbital put one electron on each open side for p electrons then pair rest of the p electrons Tro, Chemistry: A Molecular Approach

Lewis Symbols of Ions Cations have Lewis symbols without valence electrons Lost in the cation formation Anions have Lewis symbols with 8 valence electrons Electrons gained in the formation of the anion Li• Li+1 Tro, Chemistry: A Molecular Approach

Lewis Theory the basis of Lewis Theory is that there are certain electron arrangements in the atom that are more stable octet rule bonding occurs so atoms attain a more stable electron configuration more stable = lower potential energy Tro, Chemistry: A Molecular Approach

Stable Electron Arrangements And Ion Charge Metals form cations by losing enough electrons to get the same electron configuration as the previous noble gas Nonmetals form anions by gaining enough electrons to get the same electron configuration as the next noble gas The noble gas electron configuration must be very stable Tro, Chemistry: A Molecular Approach

Octet Rule when atoms bond, they tend to gain, lose, or share electrons to result in 8 valence electrons ns2np6 noble gas configuration many exceptions H, Li, Be, B attain an electron configuration like He He = 2 valence electrons Li loses its one valence electron H shares or gains one electron though it commonly loses its one electron to become H+ Be loses 2 electrons to become Be2+ though it commonly shares its two electrons in covalent bonds, resulting in 4 valence electrons B loses 3 electrons to become B3+ though it commonly shares its three electrons in covalent bonds, resulting in 6 valence electrons expanded octets for elements in Period 3 or below using empty valence d orbitals Tro, Chemistry: A Molecular Approach

Properties of Ionic Compounds Melting an Ionic Solid hard and brittle crystalline solids all are solids at room temperature melting points generally > 300C the liquid state conducts electricity the solid state does not conduct electricity many are soluble in water the solution conducts electricity well Tro, Chemistry: A Molecular Approach

Conductivity of NaCl in NaCl(s), the ions are stuck in position and not allowed to move to the charged rods in NaCl(aq), the ions are separated and allowed to move to the charged rods Tro, Chemistry: A Molecular Approach

Lewis Theory and Ionic Bonding Lewis symbols can be used to represent the transfer of electrons from metal atom to nonmetal atom, resulting in ions that are attracted to each other and therefore bond Li + + Tro, Chemistry: A Molecular Approach

Predicting Ionic Formulas Using Lewis Symbols electrons are transferred until the metal loses all its valence electrons and the nonmetal has an octet numbers of atoms are adjusted so the electron transfer comes out even 2 Li + Li2O Tro, Chemistry: A Molecular Approach

Energetics of Ionic Bond Formation the ionization energy of the metal is endothermic Na(s) → Na+(g) + 1 e ─ DH° = +603 kJ/mol the electron affinity of the nonmetal is exothermic ½Cl2(g) + 1 e ─ → Cl─(g) DH° = ─ 227 kJ/mol generally, the ionization energy of the metal is larger than the electron affinity of the nonmetal, therefore the formation of the ionic compound should be endothermic but the heat of formation of most ionic compounds is exothermic and generally large; Why? Na(s) + ½Cl2(g) → NaCl(s) DH°f = -410 kJ/mol Tro, Chemistry: A Molecular Approach

Ionic Bonds electrostatic attraction is nondirectional!! no direct anion-cation pair no ionic molecule chemical formula is an empirical formula, simply giving the ratio of ions based on charge balance ions arranged in a pattern called a crystal lattice every cation surrounded by anions; and every anion surrounded by cations maximizes attractions between + and - ions Tro, Chemistry: A Molecular Approach

Lattice Energy the lattice energy is the energy released when the solid crystal forms from separate ions in the gas state always exothermic hard to measure directly, but can be calculated from knowledge of other processes lattice energy depends directly on size of charges and inversely on distance between ions Tro, Chemistry: A Molecular Approach

Born-Haber Cycle method for determining the lattice energy of an ionic substance by using other reactions use Hess’s Law to add up heats of other processes DH°f(salt) = DH°f(metal atoms, g) + DH°f(nonmetal atoms, g) + DH°f(cations, g) + DH°f(anions, g) + DH°f(crystal lattice) DH°f(crystal lattice) = Lattice Energy metal atoms (g)  cations (g), DH°f = ionization energy don’t forget to add together all the ionization energies to get to the desired cation M2+ = 1st IE + 2nd IE nonmetal atoms (g)  anions (g), DH°f = electron affinity Tro, Chemistry: A Molecular Approach

Born-Haber Cycle for NaCl Tro, Chemistry: A Molecular Approach

Practice - Given the Information Below, Determine the Lattice Energy of MgCl2 Mg(s) ® Mg(g) DH1°f = +147.1 kJ/mol ½ Cl2(g) ® Cl(g) DH2°f = +121.3 kJ/mol Mg(g) ® Mg+1(g) DH3°f = +738 kJ/mol Mg+1(g) ® Mg+2(g) DH4°f = +1450 kJ/mol Cl(g) ® Cl-1(g) DH5°f = -349 kJ/mol Mg(s) + Cl2(g) ® MgCl2(s) DH6°f = -641.3 kJ/mol Tro, Chemistry: A Molecular Approach

Practice - Given the Information Below, Determine the Lattice Energy of MgCl2 Mg(s) ® Mg(g) DH1°f = +147.1 kJ/mol ½ Cl2(g) ® Cl(g) DH2°f = +121.3 kJ/mol Mg(g) ® Mg+1(g) DH3°f = +738 kJ/mol Mg+1(g) ® Mg+2(g) DH4°f = +1450 kJ/mol Cl(g) ® Cl-1(g) DH5°f = -349 kJ/mol Mg(s) + Cl2(g) ® MgCl2(s) DH6°f = -641.3 kJ/mol Tro, Chemistry: A Molecular Approach

Trends in Lattice Energy Ion Size the force of attraction between charged particles is inversely proportional to the distance between them larger ions mean the center of positive charge (nucleus of the cation) is farther away from negative charge (electrons of the anion) larger ion = weaker attraction = smaller lattice energy Tro, Chemistry: A Molecular Approach

Lattice Energy vs. Ion Size Metal Chloride Lattice Energy (kJ/mol) LiCl -834 NaCl -787 KCl -701 CsCl -657 Tro, Chemistry: A Molecular Approach

Trends in Lattice Energy Ion Charge -910 kJ/mol the force of attraction between oppositely charged particles is directly proportional to the product of the charges larger charge means the ions are more strongly attracted larger charge = stronger attraction = larger lattice energy of the two factors, ion charge generally more important Lattice Energy = -3414 kJ/mol Tro, Chemistry: A Molecular Approach

Example 9.2 – Order the following ionic compounds in order of increasing magnitude of lattice energy. CaO, KBr, KCl, SrO First examine the ion charges and order by product of the charges Ca2+& O2-, K+ & Br─, K+ & Cl─, Sr2+ & O2─ (KBr, KCl) < (CaO, SrO) Then examine the ion sizes of each group and order by radius; larger < smaller (KBr, KCl) same cation, Br─ > Cl─ (same Group) (CaO, SrO) same anion, Sr2+ > Ca2+ (same Group) KBr < KCl < SrO < CaO KBr < KCl < (CaO, SrO) Tro, Chemistry: A Molecular Approach

Ionic Bonding Model vs. Reality ionic compounds have high melting points and boiling points MP generally > 300°C all ionic compounds are solids at room temperature because the attractions between ions are strong, breaking down the crystal requires a lot of energy the stronger the attraction (larger the lattice energy), the higher the melting point Tro, Chemistry: A Molecular Approach

Ionic Bonding Model vs. Reality ionic solids are brittle and hard the position of the ion in the crystal is critical to establishing maximum attractive forces – displacing the ions from their positions results in like charges close to each other and the repulsive forces take over + - + - + - Tro, Chemistry: A Molecular Approach

Ionic Bonding Model vs. Reality ionic compounds conduct electricity in the liquid state or when dissolved in water, but not in the solid state to conduct electricity, a material must have charged particles that are able to flow through the material in the ionic solid, the charged particles are locked in position and cannot move around to conduct in the liquid state, or when dissolved in water, the ions have the ability to move through the structure and therefore conduct electricity Tro, Chemistry: A Molecular Approach

Covalent Bonds nonmetals have relatively high ionization energies, so it is difficult to remove electrons from them when nonmetals bond together, it is better in terms of potential energy for the atoms to share valence electrons potential energy lowest when the electrons are between the nuclei shared electrons hold the atoms together by attracting nuclei of both atoms Tro, Chemistry: A Molecular Approach

Single Covalent Bonds •• •• • • •• •• O H F O H F two atoms share a pair of electrons 2 electrons one atom may have more than one single bond H • O •• F •• • H O •• F •• F Tro, Chemistry: A Molecular Approach

Double Covalent Bond •• • •• • •• two atoms sharing two pairs of electrons 4 electrons O •• • O •• • O •• Tro, Chemistry: A Molecular Approach

Triple Covalent Bond •• • •• • •• two atoms sharing 3 pairs of electrons 6 electrons N •• • N •• • N •• Tro, Chemistry: A Molecular Approach

Covalent Bonding Predictions from Lewis Theory Lewis theory allows us to predict the formulas of molecules Lewis theory predicts that some combinations should be stable, while others should not because the stable combinations result in “octets” Lewis theory predicts in covalent bonding that the attractions between atoms are directional the shared electrons are most stable between the bonding atoms resulting in molecules rather than an array Tro, Chemistry: A Molecular Approach

Covalent Bonding Model vs. Reality molecular compounds have low melting points and boiling points MP generally < 300°C molecular compounds are found in all 3 states at room temperature melting and boiling involve breaking the attractions between the molecules, but not the bonds between the atoms the covalent bonds are strong the attractions between the molecules are generally weak the polarity of the covalent bonds influences the strength of the intermolecular attractions Tro, Chemistry: A Molecular Approach

Intermolecular Attractions vs. Bonding Tro, Chemistry: A Molecular Approach

Ionic Bonding Model vs. Reality some molecular solids are brittle and hard, but many are soft and waxy the kind and strength of the intermolecular attractions varies based on many factors the covalent bonds are not broken, however, the polarity of the bonds has influence on these attractive forces Tro, Chemistry: A Molecular Approach

Ionic Bonding Model vs. Reality molecular compounds do not conduct electricity in the liquid state molecular acids conduct electricity when dissolved in water, but not in the solid state in molecular solids, there are no charged particles around to allow the material to conduct when dissolved in water, molecular acids are ionized, and have the ability to move through the structure and therefore conduct electricity Tro, Chemistry: A Molecular Approach

Bond Polarity covalent bonding between unlike atoms results in unequal sharing of the electrons one atom pulls the electrons in the bond closer to its side one end of the bond has larger electron density than the other the result is a polar covalent bond bond polarity the end with the larger electron density gets a partial negative charge the end that is electron deficient gets a partial positive charge Tro, Chemistry: A Molecular Approach

HF EN 2.1 EN 4.0 H F • d+ d- Tro, Chemistry: A Molecular Approach

Electronegativity measure of the pull an atom has on bonding electrons increases across period (left to right) and decreases down group (top to bottom) fluorine is the most electronegative element francium is the least electronegative element the larger the difference in electronegativity, the more polar the bond negative end toward more electronegative atom Tro, Chemistry: A Molecular Approach

Electronegativity Scale Tro, Chemistry: A Molecular Approach

Electronegativity and Bond Polarity If difference in electronegativity between bonded atoms is 0, the bond is pure covalent equal sharing If difference in electronegativity between bonded atoms is 0.1 to 0.4, the bond is nonpolar covalent If difference in electronegativity between bonded atoms 0.5 to 1.9, the bond is polar covalent If difference in electronegativity between bonded atoms larger than or equal to 2.0, the bond is ionic 0.4 2.0 4.0 4% 51% Percent Ionic Character Electronegativity Difference “100%”

Bond Polarity ENCl = 3.0 ENH = 2.1 3.0 – 2.1 = 0.9 Polar Covalent ENNa = 1.0 3.0 – 0.9 = 2.1 Ionic ENCl = 3.0 3.0 - 3.0 = 0 Pure Covalent Tro, Chemistry: A Molecular Approach

Tro, Chemistry: A Molecular Approach

Bond Dipole Moments the dipole moment is a quantitative way of describing the polarity of a bond a dipole is a material with positively and negatively charged ends measured dipole moment, m, is a measure of bond polarity it is directly proportional to the size of the partial charges and directly proportional to the distance between them m = (q)(r) not Coulomb’s Law measured in Debyes, D the percent ionic character is the percentage of a bond’s measured dipole moment to what it would be if full ions Tro, Chemistry: A Molecular Approach

Dipole Moments Tro, Chemistry: A Molecular Approach

Water – a Polar Molecule stream of water attracted to a charged glass rod stream of hexane not attracted to a charged glass rod Tro, Chemistry: A Molecular Approach

Example 9.3(c) - Determine whether an N-O bond is ionic, covalent, or polar covalent. Determine the electronegativity of each element N = 3.0; O = 3.5 Subtract the electronegativities, large minus small (3.5) - (3.0) = 0.5 If the difference is 2.0 or larger, then the bond is ionic; otherwise it’s covalent difference (0.5) is less than 2.0, therefore covalent If the difference is 0.5 to 1.9, then the bond is polar covalent; otherwise it’s covalent difference (0.5) is 0.5 to 1.9, therefore polar covalent Tro, Chemistry: A Molecular Approach

Lewis Structures of Molecules shows pattern of valence electron distribution in the molecule useful for understanding the bonding in many compounds allows us to predict shapes of molecules allows us to predict properties of molecules and how they will interact together Tro, Chemistry: A Molecular Approach

Lewis Structures B C N O F use common bonding patterns C = 4 bonds & 0 lone pairs, N = 3 bonds & 1 lone pair, O= 2 bonds & 2 lone pairs, H and halogen = 1 bond, Be = 2 bonds & 0 lone pairs, B = 3 bonds & 0 lone pairs often Lewis structures with line bonds have the lone pairs left off their presence is assumed from common bonding patterns structures which result in bonding patterns different from common have formal charges B C N O F Tro, Chemistry: A Molecular Approach

Writing Lewis Structures of Molecules HNO3 Write skeletal structure H always terminal in oxyacid, H outside attached to O’s make least electronegative atom central N is central Count valence electrons sum the valence electrons for each atom add 1 electron for each − charge subtract 1 electron for each + charge N = 5 H = 1 O3 = 3∙6 = 18 Total = 24 e- Tro, Chemistry: A Molecular Approach

Writing Lewis Structures of Molecules HNO3 Attach central atom to the surrounding atoms with pairs of electrons and subtract from the total Electrons Start 24 Used 8 Left 16 Tro, Chemistry: A Molecular Approach

Writing Lewis Structures of Molecules HNO3 Complete octets, outside-in H is already complete with 2 1 bond and re-count electrons N = 5 H = 1 O3 = 3∙6 = 18 Total = 24 e- Electrons Start 24 Used 8 Left 16 Electrons Start 16 Used 16 Left 0 Tro, Chemistry: A Molecular Approach

Writing Lewis Structures of Molecules HNO3 If all octets complete, give extra electrons to central atom. elements with d orbitals can have more than 8 electrons Period 3 and below If central atom does not have octet, bring in electrons from outside atoms to share follow common bonding patterns if possible Tro, Chemistry: A Molecular Approach

Practice - Lewis Structures CO2 SeOF2 NO2-1 H3PO4 SO3-2 P2H4 Tro, Chemistry: A Molecular Approach

Practice - Lewis Structures CO2 SeOF2 NO2-1 16 e- H3PO4 SO3-2 P2H4 :O::C::O: : 32 e- 26 e- 26 e- 18 e- 14 e- Tro, Chemistry: A Molecular Approach

FC = valence e- - nonbonding e- - ½ bonding e- Formal Charge during bonding, atoms may wind up with more or less electrons in order to fulfill octets - this results in atoms having a formal charge FC = valence e- - nonbonding e- - ½ bonding e- left O FC = 6 - 4 - ½ (4) = 0 S FC = 6 - 2 - ½ (6) = +1 right O FC = 6 - 6 - ½ (2) = -1 sum of all the formal charges in a molecule = 0 in an ion, total equals the charge • •• O S O Tro, Chemistry: A Molecular Approach

Writing Lewis Formulas of Molecules (cont’d) Assign formal charges to the atoms formal charge = valence e- - lone pair e- - ½ bonding e- follow the common bonding patterns +1 -1 all 0 Tro, Chemistry: A Molecular Approach

Common Bonding Patterns F C B N O C + N + O + F + B - N - O - C - - F Tro, Chemistry: A Molecular Approach

Practice - Assign Formal Charges CO2 SeOF2 NO2-1 H3PO4 SO3-2 P2H4 Tro, Chemistry: A Molecular Approach

Practice - Assign Formal Charges -1 CO2 SeOF2 NO2-1 H3PO4 SO3-2 P2H4 P = +1 rest 0 all 0 -1 -1 Se = +1 -1 S = +1 -1 -1 all 0 Tro, Chemistry: A Molecular Approach

Resonance when there is more than one Lewis structure for a molecule that differ only in the position of the electrons, they are called resonance structures the actual molecule is a combination of the resonance forms – a resonance hybrid it does not resonate between the two forms, though we often draw it that way look for multiple bonds or lone pairs •• • O S O O S O Tro, Chemistry: A Molecular Approach

Resonance Tro, Chemistry: A Molecular Approach

Ozone Layer Tro, Chemistry: A Molecular Approach

Rules of Resonance Structures Resonance structures must have the same connectivity only electron positions can change Resonance structures must have the same number of electrons Second row elements have a maximum of 8 electrons bonding and nonbonding third row can have expanded octet Formal charges must total same Better structures have fewer formal charges Better structures have smaller formal charges Better structures have − formal charge on more electronegative atom Tro, Chemistry: A Molecular Approach

Drawing Resonance Structures draw first Lewis structure that maximizes octets assign formal charges move electron pairs from atoms with (-) formal charge toward atoms with (+) formal charge if (+) fc atom 2nd row, only move in electrons if you can move out electron pairs from multiple bond if (+) fc atom 3rd row or below, keep bringing in electron pairs to reduce the formal charge, even if get expanded octet. -1 -1 +1 -1 +1 Tro, Chemistry: A Molecular Approach

Exceptions to the Octet Rule expanded octets elements with empty d orbitals can have more than 8 electrons odd number electron species e.g., NO will have 1 unpaired electron free-radical very reactive incomplete octets B, Al Tro, Chemistry: A Molecular Approach

Drawing Resonance Structures draw first Lewis structure that maximizes octets assign formal charges move electron pairs from atoms with (-) formal charge toward atoms with (+) formal charge if (+) fc atom 2nd row, only move in electrons if you can move out electron pairs from multiple bond if (+) fc atom 3rd row or below, keep bringing in electron pairs to reduce the formal charge, even if get expanded octet. -1 +2 -1 Tro, Chemistry: A Molecular Approach

Practice - Identify Structures with Better or Equal Resonance Forms and Draw Them -1 CO2 SeOF2 NO2-1 H3PO4 SO3-2 P2H4 P = +1 all 0 -1 -1 Se = +1 -1 S = +1 -1 -1 all 0 Tro, Chemistry: A Molecular Approach

Practice - Identify Structures with Better or Equal Resonance Forms and Draw Them CO2 SeOF2 NO2-1 H3PO4 SO3-2 P2H4 -1 all 0 none +1 -1 all 0 S = 0 in all res. forms +1 -1 -1 none Tro, Chemistry: A Molecular Approach

Bond Energies chemical reactions involve breaking bonds in reactant molecules and making new bond to create the products the DH°reaction can be calculated by comparing the cost of breaking old bonds to the profit from making new bonds the amount of energy it takes to break one mole of a bond in a compound is called the bond energy in the gas state homolytically – each atom gets ½ bonding electrons Tro, Chemistry: A Molecular Approach

Trends in Bond Energies the more electrons two atoms share, the stronger the covalent bond C≡C (837 kJ) > C=C (611 kJ) > C−C (347 kJ) C≡N (891 kJ) > C=N (615 kJ) > C−N (305 kJ) the shorter the covalent bond, the stronger the bond Br−F (237 kJ) > Br−Cl (218 kJ) > Br−Br (193 kJ) bonds get weaker down the column Tro, Chemistry: A Molecular Approach

Using Bond Energies to Estimate DH°rxn the actual bond energy depends on the surrounding atoms and other factors we often use average bond energies to estimate the DHrxn works best when all reactants and products in gas state bond breaking is endothermic, DH(breaking) = + bond making is exothermic, DH(making) = − DHrxn = ∑ (DH(bonds broken)) + ∑ (DH(bonds formed)) Tro, Chemistry: A Molecular Approach

Estimate the Enthalpy of the Following Reaction

Estimate the Enthalpy of the Following Reaction H2(g) + O2(g) ® H2O2(g) reaction involves breaking 1mol H-H and 1 mol O=O and making 2 mol H-O and 1 mol O-O bonds broken (energy cost) (+436 kJ) + (+498 kJ) = +934 kJ bonds made (energy release) 2(464 kJ) + (142 kJ) = -1070 DHrxn = (+934 kJ) + (-1070. kJ) = -136 kJ (Appendix DH°f = -136.3 kJ/mol) Tro, Chemistry: A Molecular Approach

Bond Lengths the distance between the nuclei of bonded atoms is called the bond length because the actual bond length depends on the other atoms around the bond we often use the average bond length averaged for similar bonds from many compounds Tro, Chemistry: A Molecular Approach

Trends in Bond Lengths the more electrons two atoms share, the shorter the covalent bond C≡C (120 pm) < C=C (134 pm) < C−C (154 pm) C≡N (116 pm) < C=N (128 pm) < C−N (147 pm) decreases from left to right across period C−C (154 pm) > C−N (147 pm) > C−O (143 pm) increases down the column F−F (144 pm) > Cl−Cl (198 pm) > Br−Br (228 pm) in general, as bonds get longer, they also get weaker Tro, Chemistry: A Molecular Approach

Bond Lengths Tro, Chemistry: A Molecular Approach

Metallic Bonds low ionization energy of metals allows them to lose electrons easily the simplest theory of metallic bonding involves the metals atoms releasing their valence electrons to be shared by all to atoms/ions in the metal an organization of metal cation islands in a sea of electrons electrons delocalized throughout the metal structure bonding results from attraction of cation for the delocalized electrons Tro, Chemistry: A Molecular Approach

Metallic Bonding Tro, Chemistry: A Molecular Approach

Metallic Bonding Model vs. Reality metallic solids conduct electricity because the free electrons are mobile, it allows the electrons to move through the metallic crystal and conduct electricity as temperature increases, electrical conductivity decreases heating causes the metal ions to vibrate faster, making it harder for electrons to make their way through the crystal Tro, Chemistry: A Molecular Approach

Metallic Bonding Model vs. Reality metallic solids conduct heat the movement of the small, light electrons through the solid can transfer kinetic energy quicker than larger particles metallic solids reflect light the mobile electrons on the surface absorb the outside light and then emit it at the same frequency Tro, Chemistry: A Molecular Approach

Metallic Bonding Model vs. Reality metallic solids are malleable and ductile because the free electrons are mobile, the direction of the attractive force between the metal cation and free electrons is adjustable this allows the position of the metal cation islands to move around in the sea of electrons without breaking the attractions and the crystal structure Tro, Chemistry: A Molecular Approach

Metallic Bonding Model vs. Reality metals generally have high melting points and boiling points all but Hg are solids at room temperature the attractions of the metal cations for the free electrons is strong and hard to overcome melting points generally increase to right across period the charge on the metal cation increases across the period, causing stronger attractions melting points generally decrease down column the cations get larger down the column, resulting in a larger distance from the nucleus to the free electrons Tro, Chemistry: A Molecular Approach