Karteikarten
6.4 Hydrogen bonding
Karten in diesem Stapel (30)
- 1What is a hydrogen bond?Special type of permanent dipole-dipole interaction
- 2Where is the hydrogen bond found between molecules containing..(2)- an electronegative atom with a lone pair of electrons eg. oxygen, nitrogen and fluorine
- a hydrogen atom attached to an electronegative atom, eg. H-0, H-N or H-F - 3Which is stronger? Induced dipole-dipole interactions Permanent dipole-dipole interactions Hydrogen bondingHydrogen bonding
- 4The hydrogen bond acts between a _____ pair of electrons on an _________ atom in one molecule and a hydrogen atom in a different molecule.lone
electronegative - 5Draw hydrogen bonding between H2O.
- 6Draw the hydrogen bond between NH3.
- 7Hydrogen is always what polarity?δ +
- 8Why is solid (ice) less dense than the liquid (water)? (3)- Hydrogen bonds hold water molecules apart in an open lattice structure
- The water molecules in ice are further apart than in water
- Solid ice is less dense than liquid water and floats - 9With two lone pairs on the oxygen atom and ___ hydrogen atoms, each water molecule can form ___ hydrogen bonds. The hydrogen bonds extend outwards, holding water molecules slightly apart and forming an open _______ lattice full of holes. The bond angle about the hydrogen atom involved in the hydrogen bond is close to ____°.two
four
tetrahedral
180° - 10What do the holes in the open lattice structure do the the water?Decrease the density of water on freezing.
When ice melts, the ice lattice collpases and the molecules move closer together. So liquid water is denser than solid ice. - 11How does water have a relatively high melting point and boiling point? (4)-Water has London forces between molecules as with all molecules
- Hydrogen bonds are extra forces, over and above the London forces
- An appreciable quantity of energy is needed to break the hydrogen bonds in water, so water has much higher melting and boiling points than would be expected from just London forces
- When the ice lattice breaks, the rigid arrangement of hydrogen bonds in ice is broken. When water boils, the hydrogen bonds break completely. - 12What wuld water be like if it did not have hydrogen bonds?Water would have a boiling point of about -75°C and would exist as gas at RTP
- 13Why do water, hydrogen fluoride and ammonia not follow the group trends?All three have hydrogen bonding which is a stronger intermolecular force than other dipole interactions. Greater energy needed to overcome the intermolecular forces, so boiling points are much higher.
- 14Explain why all groups show an increase in boiling point from Period 3 to Period 6.Increase in electrons increases the strength of the London forces
- 15What conclusions can be drawn about the relative strengths of London forces and permanent dipole-dipole interactions for the hydrides of Groups 14-17? (4-7)From Period 3 to Period 6, difference in electronegativity between hydroen and element decreases, decreasing the permanent dipole-dipole interactions. Number of electrons increases, increasing London forces. Boiling point increases so London forces are stronger and more significant than the permanent dipole-dipole interactions.
- 16What are other anomalous properties of water?Relatively high surface tension and viscosity
- 17Why does HF have a higher boiling point than HCl?Hydrogen bonding. More energy is needed to overcome the electrostatic forces.
Slight increase in boiling point from HCl to HI due to increased mass of molecule, hence the bigger electron cloud and more induced dipole-dipole forces. - 18Molecules that have hydrogen bonding also have what?Induced dipole-dipoe
Permanent dipole-dipole - 19How is the double helix structure of DNA held together?Hydrogen bonds which enable a single DNA strand to create a perfect copy of itself in replication.
- 20The replication of DNA depends on what 4 bases?Adenine
Thymine
Cytosine
Guanine - 21A and T pair by forming how many hydrogen bonds?2
- 22C and G pair by forming how many hydrogen bonds?3
- 23Why do the C-G and A-T pair up?Chemical structure and shape of these four bases ensure correct pairing.
- 24Adenine and Guanine are both _____ bases with ____-ringed structures.Purine
Two - 25Thymine and Cytosine are both ______ bases with ____-ringed structures.Pyrimidine
Single - 26Hydrogen bonding in a double helix can only take place between a _____ and _______ base.Purine and Pyrimidine
- 27The bases must fit together so that a hydrogen atom from one molecule and an ____________ atom (oxygen or nitrogen) from the other molecule are aligned correctly to maximise hydrogen bonding.electronegative
- 28Suggest why pairing does not take place between two purine bases or between two pyrimidine bases.Two purine bases would be too close together
Two pyrimidine bases would be too far apart - 29State which of the following compounds have hydrogen bonding. H2O H2S CH4 CH3OH NO2H2O
CH3OH - 30Draw diagrams showing two ways that hydrogen bonding can form between: One molecule of water and one molecule of ethanol, CH3CH2OH
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- A level Chemistry (Module 2: Foundations in Chemistry) Karteikarten am 6.4 Hydrogen bonding, erstellt von Urvi B am 20/12/2017.
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