INTERMOLECULAR FORCES (IMF)

INTERMOLECULAR FORCES ARE BETWEEN MOLECULES WHEREAS INTRAMOLECULAR FORCES ARE WITHIN THE MOLECULE INTERMOLECULAR FORCES ARE: 1.)Van der Waal forces (also called London dispersion forces) 2.)dipole-dipole forces 3.)hydrogen bonding INTRAMOLECULAR FORCES ARE:(ionic, covalent & metallic)

Van der Waal forces (London Dispersion Forces) Are the weakest IMF Exists between nonpolar molecules and noble gases Occur when temporary dipoles(positive end- negative end) form within a molecule Since electrons are in constant motion, there are times when the electrons are more concentrated in one location more than another. This causes that area to be more negative than the other side creating the temporary or instantaneous dipole

Van der Waal forces (London Dispersion Forces) Properties Low melting & boiling points The Van der Waal forces increase with increasing size of the molecule so that makes the melting & boiling point also increase with increasing size Example: CH 4 < C 2 H 6 < C 3 H 8 < C 4 H 10 or F 2 <Cl 2 <Br 2 <I 2

DIPOLE-DIPOLE FORCES Are stronger than Van der Waal forces but weaker than hydrogen bonding Exist between polar molecules( polar molecules have permanent dipoles) The negative side of one molecule is attracted to the positive side of another molecule

DIPOLE-DIPOLE FORCES PROPERTIES Have higher melting & boiling points than that of nonpolar molecules of the same size( approx. same molar mass) The strength of the dipole-dipole forces decreases as the degree of polarity decreases Example: HCl > HBr>HI b/c the electronegativity values decreases from Cl to I so H-Cl bond is more polar than H-I

HYDROGEN BONDING It is a type of dipole-dipole force but exist only between hydrogen covalently bonded to either nitrogen, oxygen or fluorine It is the strongest of the IMFs

HYDROGEN BONDING PROPERTIES These molecules have the highest melting and boiling points of all other covalent compounds If it wasn’t for the fact that it is hydrogen bonded, water would be a gas not a liquid at room temperature. This is also why water is less dense as a solid than a liquid. The water molecule is capable of bonding in 4 locations to another water molecule. As the molecules get closer, a tetrahedral arrangement holds the molecules a fixed distance away creating a fairly open structure.

HYDROGEN BONDING Hydrogen bonding plays a role is so many molecules and the properties they have. Proteins and DNA just to name a few, are held together by hydrogen bonds

Explain why the Higher Molar Mass Compound, CF 4, has a Lower Boiling Point than H 2 Se CF 4 Boiling Point; °C Molar Mass ~ 88 g/mole H 2 Se Boiling Point; °C Molar Mass ~ 81 g/mole Intermolecular Force; Dispersion Force Intermolecular Force; Dipole- Dipole Force

SOLUBILITY Most polar molecules(except for large molecules) are soluble in water due to the attraction between their dipoles and those of water Nonpolar molecules are not soluble in water However nonpolar molecules are soluble in other nonpolar solvents “LIKES DISSOLVE LIKE”

INTRAMOLECULAR vs INTERMOLECULAR FORCES Intramolecular forces are much stronger than intermolecular forces. Ionic and metallic bonds are much stronger than covalent bonds INTERMOLECULAR FORCES Van der Waal<Dipole-dipole< hydrogen bonding

SOLUBILITY IONIC COMPOUNDS POLAR COVALENT COMPOUNDS NON-POLAR COMPOUNDS SOLUBITITY IN POLAR SOLVENTS SOLUBLESOLUBILITY INCREASES AS POLARITY INCREASES NON-SOLUBLE SOLUBILITY IN NON-POLAR SOLVENTS NON-SOLUBLESOLUBILITY INCREASES AS POLARITY DECREASES SOLUBLE

IB INTERNAL ASSESSMENT ASSESSED FOR : DESIGN DATA COLLECTION AND PROCESS & CONCLUSION AND EVALUATION

INVESTIGATE A PARAMETER THAT AFFECTS THE SOLUBILITY OF SALTS MADE FROM GROUP 1METALS AND HALOGENS (GROUP 7)

Common salt is soluble in water. That does not mean that we can dissolve infinite amounts of salt in a specific amount of water. There is a certain point where no more salt will dissolve. o How can we measure what is the maximum mass of salt that can dissolve in a specific volume of water o Do we have to measure how much has been dissolved or is it enough to measure how much has not been dissolved. o Do we have to measure the salt itself or we can measure one of it’s ions.

What factors may effect solubility? If we change the metal part of the salt, will solubility change If we change the temperature of water, will solubility change If we change solvent, will the solubility change What other parameters may affect solubility

SELECT DEPENDENT, INDEPENDENT AND CONTROLLED VARIABLES, WRITE YOUR SPECIFIC RESEARCH QUESTION AND DESCRIBE THE DETAILED PROCEDURE REQUIRED TO INVESTIGATE THE QUESTION WRITE THE REPORT INCLUDING ALL COMPONENTS

CHEMICALS AVAILABLE: Lithium chloride Potassium fluoride Potassium chloride Potassium bromide Potassium iodide Sodium fluoride Sodium chloride Sodium bromide