Flashcards
6.3 Intermolecular forces
Cards in this deck (43)
- 1What are intermolecular forces?Weak interactions between dipoles of different molecules.(Forces between molecules)
- 2Intermolecular forces fall into which 3 categories?Induced dipole-dipole interactions (London forces)
Permanent dipole-dipole interactions
Hydrogen bonding - 3Intermolecular forces are largely responsible for what?Physical properties such as melting and boiling points.
- 4Covalent bonds determine what?Identity and chemical reactions of molecules
- 5What are induced dipole-dipole interactions? (London forces)Weak intermolecular forces that exist between all molecules, whether polar or non-polar. They act between induced dipoles in different molecules.
- 6What is the origin of induced dipoles?- Movement of electrons produced a changing dipole in a molecule
- At any instant, an instantaneous dipole will exist, but its position is constantly shifting
- The instantaneous dipole induces a dipole on a neighbouring molecule
- The induced dipole induces further dipoles on neighbouring molecules, which then attract one another - 7Are induced dipoles temporary or permanent?Temporary
- 8Induced dipoles result from interactions of electrons between molecules. The more electrons in each molecule ....(3)- The larger the instantaneous and induced dipoles
- The greater the induced dipole-dipole interactions
- The stronger the attractive forces between molecules - 9What is the correlation between larger induced dipoles and boiling point?- Larger numbers of electrons mean larger induced dipoles
- More energy is then needed to overcome the intermolecular forces, increasing the boiling point - 10What are permanent dipole-dipole interactions?Permanent dipole-dipole interactions act between the permanent dipoles in different polar molecules. The δ+ and δ- charges on polar molecules cause weak electrostatic forces of attraction between molecules
- 11Polar molecules have ______ dipole interactions as well as permanent dipole-dipole interactions.Induced
- 12Draw a diagram showing permanent dipole-dipole interactions between hydrogen chloride, HCl, molecules.
- 13HCl and F2 have the same number of electrons and the same shape, so the strength of the London forces in hydrogen chloride and fluorine should be similar. Why is HCl's boiling point higher than fluorine?- Fluorine molecules are non-polar and only have London forces between molecules
- Hydrogen chloride molecules are polar and have London forces and permanent dipole-dipole interactions between molecules
- Extra energy is needed to break the additional permanent dipole-dipole interactions between hydrogen chloride molecules
- The boiling point of hydrogen chloride is therefore higher than fluorine
- 14In a solid state, simple molecules form a regular structure called what?Simple molecular lattice
- 15What is in the simple molecular lattice?- the molecules are held in place by weak intermolecular forces
- the atoms within each molecule are bonding together strongly by covalent bonds - 16Do simple molecular substances have high or low melting and boiling points?Low
- 17What happens when simple molecular substances are solidified into simple molecular lattices by reducing the temperature?- In a simple molecular lattice, the weak intermolecular forces can be broken even by the energy present at low temperatures
- Simple molecular substances have low melting and boiling points - 18What happens when a simple molecular lattice is broken apart during melting?- only the weak intermolecular forces break
- the covalent bonds are strong and do not break - 19Why are non-polar simple molecular substances soluble in non-polar solvents?- When a simple molecular compound is added to a non-polar solvent, such as hexane, intermolecular forces form between the molecules and the solvent
- The interactions weaken the intermolecular forces in the simple molecular lattice. The intermolecular forces break and the compound dissolves. - 20Why are simple molecular substances non-polar insoluble in polar solvents?- When a simple molecular substance is added to a polar solvent, there is little interaction between the molecules in the lattice and the solvent molecules
- The intermolecular bonding within the polar solvent is too strong to be broken - 21Can polar covalent substances dissolve in polar solvents?Yes
Polar solute molecules and polar solvent molecules can attract each other - 22What does solubility depend on?Strength of the dipole and can be hard to predict
- 23Give example of strength of dipole.Ethanol C2H5OH, contains both polar (O-H) and non-polar (carbon chain) parts in their structure and can dissolve in polar and non-polar solvents
- 24What happens when some biological molecules have hydrophobic and hydrophilic parts? (Solubility)Hydrophilic part will be polar and contain electronegative atoms (oxygen) and can interact with water
Hydrophobic part will be non-polar and comprised of a carbon chain - 25Property of electrical conductivity in simple molecular substances.- There are no mobile charged particles in simple molecular structures
- With no charged particles that can move, there is nothing to complete and electrical circuit.
Non-conductors of electricity - 26Permanent dipole-dipole interactions exist in molecules with a what?Polarity
- 27The δ+ is acctracted to what?δ- of another molecule
- 28There are weak what forces that exist between molecules with a polarity?Intermolecular forces
- 29Unlike induced dipole-dipole forces, permanent dipole-dipole interactions involves molecules with a permanent dipole and so are ________.Stronger
- 30How can polar molecules like water be tested?Placing a charged rod near a steady stream of polar liquid.
You should see the liquid bent towards the rod as the molecules align to face the oppositely charged rod. - 31What determines the strength of London forces?Larger molecules have larger electron clouds, meaning stronger London forces
Molecules with greater surface areas have stronger London forces as they have a more exposed electron cloud - 32In what elements can hydrogen bonding occur?Hydrogen covalently bonded to fluorine, nitrogen or oxygen
- 33How are hydrogen bonds formed?Hydrogen has a high charge density because it's so small and fluorine, nitrogen and oxygen are very electronegative. The bond is so polarised that a weak bond forms between the hydrogen of one molecule and a lone pair of electrons on the fluorine, nitrogen or oxygen in another molecule.
- 34What effect does hydrogen bonding have on the properties of substances?Substances are soluble in water and have higher boiling and melting points than molecules of a similar size that are unable to form H bonds.
E.g. water and ammonia have very high boiling points when compared to other hydrides in their groups - 35Why do molecules which are able to form hydrogen bonds have very high boiling/melting points?Extra energy is needed to break the hydrogen bonds
- 36Why do molecules which are able to form hydrogen bonds have very high boiling/melting points?Extra energy is needed to break the hydrogen bonds
- 37Explain why ice is less dense than liquid waterIn ice, molecules of H₂O are held together in a lattice by hydrogen bonds. Since hydrogen bonds are relatively long, the molecules in ice will be further apart than in liquid water - this makes ice less dense than liquid water
- 38What is the main factor that determines the boiling point?The strength of the London forces (unless the molecule can form hydrogen bonds)
- 39Explain how the strength of the London forces between molecules determines the boiling pointIf two molecules have a similar number of electrons, then the strength of the London forces will be similar. So if one of the substances has molecules that are more polar than the other, it will have stronger permanent dipole-dipole interactions and so a higher boiling point. For example, the boiling points of the Group 7 hybrids increases - the strength of the increasing strength of London forces has a higher effect than the decreasing strength of the permanent dipole-dipole interactions.
- 40hydrogen bonding is the strongest intermolecular
- 41hydrogen bonds affect how a substance behaves how group 7 boiling points hydrides vary as you go down 7
- 42hydrogen bonds affect how a substance behaves how group 6 boiling points hydrides vary as you go down 6
- 43—
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- A level Chemistry Flashcards on 6.3 Intermolecular forces, created by megan trent on 18/05/2018.
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- Created by Urvi B · Dec 13, 2017
- Copied by megan trent · May 18, 2018
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