Top2-Ch2-P43-46Reverse Flashcards
Water has higher melting point, boiling point, and heat of vaporisation than most common solvents
Water has a higher (three things) more than most common solvents.
covalent, unequal
For water. It has a ________ bond with the e- being shared _________ between H and O.
O more electronegative so attracts e-
H2O = polar compound
Which is more electronegative (tendency to attract electrons) in water molecule O or H?
And is H2O polar or not?
CH2O
What is the seawater molecule?
104.5 degrees
What is the angle of a H-O-H bond in water?
Hydrogen acceptors: Electronegative atoms (usually O or N, Not C)
Hydrogen donors: H atoms covalently bonded to an electronegative atom
Uneven e- sharing → electrostatic attraction
This allows the formation of H-bonds :
which are longer & weaker than covalent bonds
wikipedia: A hydrogen bond is the electromagnetic attractive interaction of a polar hydrogen atom in a molecule or chemical group and an electronegative atom, such as nitrogen, oxygen or fluorine, from another molecule or chemical group. It is not a covalent chemical bond.
See hydrogen bond in picture below compared to covalent bond.
(S also slightly electronegative)
Hydrogen bonding explain
Energy required to break a bond.
Hydrogen bond dissocation energy is: 23kj/mol while O-H covalent bond in water is 470kj/mol or a covalent C-C bond is 348kj/mol
What is bond dissociation energy? And compare hydrogen bonds to other covalent bonds.
When one hydrogen bond breaks another hydrogen bond forms with the same partner or a new one within 0.1ps (1ps = 10-12seconds)
What is “flickering clusters” in context of hydrogen bonding?
Up to four
How many hydrogen bonds can each water molecule form with neighbouring water molecules?
- 4 H bonds each water molecule
- Crystal lattice structure
- Less dense than liquid water, floats on water and insulates lower layers
See lattice below of frozen water
Explain ice (solid state of water)? Bonds, structure type and density.
Average bond 3.4H bonds
Lifetime range of flickering clusters is 1-20ps
(1ps = 10-12 seconds)
In liquid water how many H bonds, on average, create the flickering clusters and what is the range of the H bond lifetime for liquid water.
- solid
- H-bonds
Water is almost ______, being held together by substantial internal cohesive forces called _______.
These determine the properties of water.
increases
∆G = ∆H - T ∆S
where;
∆G is free energy change the driving force
∆H is the enthalpy change from making and breaking bonds
∆S is the change in randomness
The ∆G must be a negative value for a process to occur spontaneously.
During melting or evaporation the entropy of the aqueous system_______
Recall formula for free energy change
Butanol (CH3(CH2)2CH2OH) : BP of 117oC.
Butane (CH3(CH2)2CH3) : BP of 0.5oC.
Butanol has a polar hydroxyl group that can form intermolecular hydrogen bonds increasing the energy required to break bonds and get it to boil.
See chart below. In chart below the properties are due to attractions (H bonds) between adjacent water molecules, which give liquid water great internal cohesion.
Note butanol vs butane
Due to just one –OH group and look at water
Explain how butanol has a higher boiling point than butane
- No
- forms hydrogen bonds with organic compounds
Are hydrogen bonds unique to water?
What type of compounds do hydrogen bonds form which are of central importance to living cells?
- Between hydroxyl group of alcohol and water
- between carbonyl group of a ketone and water
- between peptide groups in polypeptides
- between complementary bases of DNA
Look at and memorise important biological H bonds. Name the four groups used.
greatest when 3 atoms involved in H bond in a straight line
When is hydrogen bond strength greatest?
