TOPIC 3 THE CHEMICAL BASIS OF LIFE

•How many elements are found on earth?

•How many of them are found in human body?

•How do we get them?

•How do plants get them?

•Why do we get them?

•Do we need these elements in equal amounts?

Chemical composition of living organisms

Trace elements

Revision of basic chemistry

•What is an element?

•What is an atom?

•Atomic structure?

•What is a molecule?

•What is a compound?

•What is an ion? (polyatomic ions)

Elements and compounds

Atomic structure

Electron arrangement

•Why do atoms bind with each other?

To make their outer shells complete so they resemble noble gases

•What happens as a result?

Energy is stored and released

Various chemical structures are formed

•What causes atoms to make bonds?

Electronegativity

Inorganic and organic molecules

• Inorganic molecules: are the molecules which do not contain carbon. (CO2, HCO3

- and carbonate are exceptions)

• Organic compounds: are the molecules which contain carbon. There are more than 10.000 different compounds.

Living things have both inorganic and organic compounds.

Intramolecular bonds a) Ionic bonding

Intramolecular bonds b) Covalent bonding

Nonpolar covalent bonds

Polar covalent bonds

•Draw a water molecule.

•Draw three water molecules that are bonded together.

•Name the bond within the water molecule.

•Name the bond between the water molecules.

•Are water molecules polar or nonpolar?

•What is the reason of the bonding between water molecules?

Polarity

Hydrogen bonding

What is the importance of polarity of water for living things?

1- Solvent of life

Do all molecules dissolve in water?

Importance for living things?

2. Cohesion and adhesion

Capillary

action

You want to have pasta for dinner so you start boiling some water in a pot. After a few minutes you touch the pot and the water inside.

Which one will feel hotter?

You are at the beach just out from the sea, walking on sand. The sand burns your feet. This puzzles you since the sea was quite refreshing.

Why does the sand burn your feet?

It’s been snowing during the last week. You realize that the ice on the sidewalk still hasn’t melted although last few days have been quite sunny and warm.

Why hasn’t the ice melted?

Specific heat capacity

The quantity of heat per unit of mass required to raise the temperature by 1 degrees Celcius

OR

ability to absorb heat energy

Does a substance that heats up quickly have high or low specific heat capacity?

temp. increase by

1g of water 10C

X amount of of heat 1g of alcohol

1g of iron

Heat of vaporizationThe amount of thermal energy needed to change a substance from liquid to gas or gas to liquid

Heat of fusionThe amount of thermal energy needed to change a substance from liquid to solid or solid to liquid

3. Temperature moderation

Why do lakes freeze on top?

4. Density of ice

Which one is ice, which one is water?

What are the functions of water in the living things?

• Temperature moderation• Solvent• Cohesion• Habitat• Chemical reactions (photosynthesis, digestion

……)

ACID AND BASES

Acids:Release H+ in aqueous solutions

HCl H+ + Cl-

Bases:Release OH+ OR Accept H+ in aqueous

solutions

NaOH Na+ + OH-

Buffers:

Solutions that stabilize pH changes. How?

Release H+ when the solution becomes too basic OR

Accept H+ when the solution becomes too acidic

Bicarbonate buffer in blood

H2O + CO2 H2CO3 HCO3 + H+