Presentation on theme: "Intermolecular Forces: relationships between molecules"— Presentation transcript:
1 Intermolecular Forces: relationships between molecules
2 Polarity and ShapePolar bonds do not necessarily always create a polar molecule.The shape of the molecule and the polarity of each bond is considered before stating if a molecule is considered POLAR or NON-POLARWe will watch a 5 minute explanation to help us understand this difficult conceptmajor intermolecular forces
4 Intramolecular forces intra = inside Intramolecular forces: forces that bond the atoms to each other within the molecule.COVALENT BONDS!!!
5 Intermolecular Forces inter = between Forces affecting the relationships between moleculesLondon Forces (Dispersion Forces) AKA van der Waals forcesDipole-Dipole InteractionsIon-dipole forcesHydrogen Bonding
6 London (dispersion) Forces aka van Der Waals forces weakest intermolecular forceoccurs between all types of moleculesIt is a temporary attractive force that results when the electrons in two adjacent atoms occupy positions that make the atoms form temporary dipoles
7 London Dispersion forces in a molecule These instantaneous dipoles may be induced and stabilized as an ion or a polar molecule approaches the non-polar molecule.
8 Dipole-Dipole Forces Dipole = polar molecule Molecules with dipoles will change their direction so that their oppositely charged ends are near to one another.The electrostatic attraction between the ends is dipole-dipole force
9 Orientation of Polar Molecules in a Solid Dipole-Dipole ForcesAttractive forces between polar moleculesOrientation of Polar Molecules in a Solid11.2
11 Ion Dipole Forces (the reason why ionic compounds dissolve in water) The force of attraction between an ion and a polar molecule.NaCl breaks up because the ion dipole with water is stronger than the attraction of Na+ to Cl-
12 Polar molecules can interact with ions: Ion - Dipole Interactions
14 A hydrogen bond is the strongest form of dipole-dipole interaction. A hydrogen bond is formed between polar molecules that contain hydrogen covalently bonded to the small, highly electronegative atoms, F, O, or N.F—HO—HN—H
15 A molecule containing this combination of atoms, will be attracted to another molecule with the same atom combination.A strong attractive force between the two molecules which is called a hydrogen bond is formed.hydrogen bondcovalent bondcovalent bond
16 water has the lowest molar mass water has the highest heat of fusion water has the highest melting pointwater has the highest boiling pointwater has the highest heat of vaporizationThe melting point, boiling point, heat of fusion and heat of vaporization of water are extremely high and do not fit the trend of properties relative to molar mass within Group 17.
17 Hydrogen bonding in water animation hydrogen bonding animationWater exhibits these unusual properties because of hydrogen bonding between water molecules.
18 Why do we care about intermolecular forces? The forces that act on molecules determine their physical propertiesStrong intermolecular forces between molecules increase melting and boiling points because it is these forces that are broken when substances change state.
19 Polarity and Boiling Point: The polarity of the molecules determines the forces of attraction between the molecules in the liquid state.Polar molecules are attracted by the opposite charge effect (the positive end of one molecule is attracted to the negative end of another molecule).Molecules have different degrees of polarity as determined by the functional group present.The greater the forces of attraction the higher the boiling point or the greater the polarity the higher the boiling point.
20 What is boiling point?Boiling point is the temperature at which a liquid turns into a gas (or vapour).For a liquid to turn into a gas, intermolecular forces must be broken.The stronger the intermolecular forces, the higher the boiling point of a substance.
21 The evidence for hydrogen bonding Many elements form compounds with hydrogen - referred to as "hydrides".If you plot the boiling points of the hydrides of the Group 4 elements, you find that the boiling points increase as you go down the group.The increase in boiling point happens because the molecules are getting larger with more electrons, and so van der Waals dispersion forces become greater.
22 The evidence for hydrogen bonding If you repeat this exercise with the hydrides of elements in Groups 5, 6 and 7, something odd happens.
23 Solubility and Intermolecular Forces Like dissolves likePolar solutes dissolve in polar solventsNonpolar solutes dissolve in nonpolar solventsMolecules with similar intermolecular forces will mix freely
30 Comparison of the Properties of Substances with Ionic, Covalent, Metallic or Intermolecular Bonds Bond strengthStrongVery strongVariable strength, generallymoderateWeakHardnessModerate to highInsulators in solids and liquid statesLow to moderate; ductile, malleableCrystal soft and somewhat plasticElectrical conductivityConducts by ion transport, but only when liquid or dissociatedLowGood conductors; conducts by electron transportInsulators in both solid and liquid statesMelting pointVery highGenerally highSolubilitySoluble in polar solventsVery low solubilityInsoluble except in acids or alkalis by chemical reactionSoluble in organic solventsExamplesMost mineralsDiamond, oxygen, hydrogen, organic moleculesCu, Ag, Au, other metalsOrganic compounds
31 Boiling Point of Various Material (˚C) Noble gasHelium neon argonHe Ne ArNonpolar covalenthydrogen oxygen methane chlorineH2 O2 CH4 Cl2polar covalentammonia hydrogen fluoride waterNH3HFH2O100ionicpotassium chloride sodium chloride magnesium oxideKClNaClMgO77114132826metalliccopper iron tungstenCu Fe W