1. Chemical Bonds Electronegativity is an atom’s affinity for electrons.
Differences in electronegativity dictate how electrons are distributed in covalent bonds.
- nonpolar covalent bonds = equal sharing of electrons
- polar covalent bonds = unequal sharing of electrons

2. Water

3. Water Chemistry
Life on earth evolved in water, and all life still depends on water.
All living organisms are dependent on water.
At least 80% of the mass of living organisms is water and almost all
chemical reactions of life take place in aqueous solution.

4. Water Chemistry
The structure of water is the basis for its unique properties.
The most important property of water is the ability to form hydrogen bonds.
Within a water molecule, the bonds between oxygen and hydrogen are highly polar.

5. Water Chemistry Electronegativity is an atom’s affinity for electrons.
Differences in electronegativity dictate how electrons are distributed in covalent bonds.
Electonegative elements?????
Electropositive elements????
polar covalent bonds = unequal sharing of electrons
Non-polar covalent bonds=equal sharing of electrons

6. Water Chemistry
Due to the polar covalent bond partial electrical charges develop:
water molecules are charged, with the oxygen atom being slightly negative (partially negative) and
the hydrogen atoms being slightly positive (partially positive).
WHY PARTIAL CHARGES?????

8. Structure of water

9. Water Chemistry
Polarity unequal charge distribution in a molecule resulting in a – region and a + region
Dipole- amphoteric????????
These opposite attract each other, forming hydrogen bonds. These are weak, long distance bonds that are very common and very important in biology.

10. Water Chemistry
Hydrogen bonds are weak attractions between the partially negative oxygen of one water molecule and the partially positive hydrogen of a different water molecule.
Hydrogen bonds can form between water molecules or between water and another charged molecule.

11. Water Properties
1.The polarity of water causes it to be cohesive and adhesive.
cohesion: water molecules stick to other water molecules by hydrogen bonding, so water has a high cohesion.
This explains why long columns of water can be suck up tall trees by transpiration without breaking.
Cohesion helps the transport of water against gravity in plants

12. Water Properties
Cohesion also explains surface tension which allows small animals to walk on water.
Surface tension is a measure of how hard it is to break the surface of a liquid
Surface tension is related to cohesion

13. Water Chemistry
cohesion

14. Water Chemistry
adhesion: water molecules stick to other polar molecules by hydrogen bonding water rises in plants due to its adhesion to capillary walls. Cohesion and adhesion produces a single, polymer-like column of water in xylem, extending from roots to leaves-capillary action

15. Properties of Water 2.Water has a high specific heat capacity.
- A large amount of energy is required to change the temperature of water.(4.2 joules of energy to heat 1g water by 1oC). This means that water does not change temperature easily. This minimises fluctuations in temperature inside cells and means that sea temperature is quite constant.

16. Water Properties
Water absorbs heat from warmer air and releases stored heat to cooler air
Water can absorb or release a large amount of heat with only a slight change in its own temperature
Water is a temperature buffer it resists changing its temperature because of its high specific heat

17. Water Properties
Water’s high specific heat can be traced to hydrogen bonding
Heat is absorbed when hydrogen bonds break
Heat is released when hydrogen bonds form
The high specific heat of water minimizes temperature fluctuations to within limits that permit life

18. Properties of Water 3has a high latent heat of vaporization.
Evaporation is transformation of a substance from liquid to gas
Heat of vaporization is the heat a liquid must absorb for 1 g to be converted to gas
As a liquid evaporates, its remaining surface cools, a process called evaporative cooling
Evaporative cooling of water helps stabilize temperatures in organisms and bodies of water

19. Water Properties
Water requires a lot of energy to change state from a liquid to a gas, providing a cooling mechanism in animals (sweating and panting) and plants (transpiration). As water evaporates it extracts heats from the surrounding area, cooling the organism
- The evaporation of water from a surface causes cooling of that surface.

20. Properties of Water
Solid water is less dense than liquid water. Water is its solid state (ice) is less dense than the liquid state.
As the air temperature cools, bodies of water freeze from the surface (top down), forming a layer of ice with the liquid beneath, T his allows aquatic ecosystem to exist in low temperatures.

23. Water Properties
Ice floats in liquid water because hydrogen bonds in ice are more “ordered,” making ice less dense
Water reaches its greatest density at 4°C
If ice sank, all bodies of water would eventually freeze solid, making life impossible on Earth

24. The three states of water
????????????

25. Ice, water, vapor

26. Three states of water

27. Three states of water

28. Water: the solvent of life
A solution is a liquid that is a homogeneous mixture of substances
A solvent is the dissolving agent of a solution
The solute is the substance that is dissolved
An aqueous solution is one in which water is the solvent

29. Water Properties
Water is a good solvent. Water dissolves polar molecules and ions.
It is a very good solvent. Molecules such as salts, sugars, amino acids, alcohols dissolve readily in water (once dissolved they can be transported e.g. glucose in the bloodstream). Water is a good/ universal solvent for charged and polar substances

30. Water as solvent
Water is a versatile solvent due to its polarity, which allows it to form hydrogen bonds easily
When an ionic compound is dissolved in water, each ion is surrounded by a sphere of water molecules called a hydration shell

31. Water as a solvent
Water can also dissolve compounds made of nonionic polar molecules
Even large polar molecules such as proteins can dissolve in water if they have ionic and polar regions

32. Water Properties HYDROPHILIC?????? HYDROPHOBIC???????
Water is a poor solvent for nonpolar substances
nonpolar gases
aromatic moieties
aliphatic chains
HYDROPHILIC??????
HYDROPHOBIC???????
AMPHIPHILE/AMPHIPATHIC????????

33. Properties of Water Water organizes nonpolar molecules.
- hydrophilic: “water-loving”
A hydrophilic substance is one that has an affinity for water
Most biochemical reactions occur in water
Chemical reactions depend on collisions of molecules and therefore on the concentration of solutes in an aqueous solution
Ionization; happens spontaneously

34. Properties of Water -hydrophobic: “water-fearing”
A hydrophobic substance is one that does not have an affinity for water
Oil molecules are hydrophobic because they have relatively nonpolar bonds

35. Properties of Water
- Water causes hydrophobic molecules to aggregate or assume specific shapes.
This means water is able to transport nutrients and waste material in living organisms .
Contributes to the integrity of the cell membrane, nucleic acids and proteins
Amphipathic

36. The Hydrophobic Effect
Refers to the association or folding of non-polar molecules in the aqueous solution
Is one of the main factors behind:
Protein folding
Protein-protein association
Formation of lipid micelles
Binding of steroid hormones to their receptors
Does not arise because of some attractive direct force between two non-polar molecules

37. ADDITIONAL PROPERTIES OF WATER
High melting point
High boiling point
High surface tension
High heat of fusion

38. SUMMARY
Many properties of water are emergent properties due to hydrogen bonding.
The cohesion of water molecules to each other is exploited by plants and animals.
Water resists temperature changes by absorbing lots of heat.
Lower density of ice causes it to float & insulate the water below.
The polarity of water allows it to dissolve other polar molecules.
Non-polar compounds are hydrophobic and not easily dissolved in water.

39. QUESTION
The remarkable properties of water support life on Earth in many ways.Explain

40. Acids and Bases Hydrogen ion (H+1) is the basis of the pH scale.
Greater H+1 concentration --- lower pH (acidic)
Lower H+1 concentration --- higher pH (basic)

41. Acids and Bases Acid: a chemical that releases H+1 ions. pH below 7
Base: a chemical that accepts H+1 ions.
pH above 7
Buffer: a chemical that accepts/releases H+1 as necessary to keep pH constant

42. Acids and Bases

43. Acids and Bases
Most biological buffers consist of a pair of molecules, one an acid and one a base.
BUFFER SYSTEM IN HUMAN BLOOD
ACID
BASE

44. Acids and Bases