learning outcomes topic 3 water and organic molecules ... · pdf filetopic 3 water and organic...

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Boardworks AS Biology

Biological Molecules: Water and Carbohydrates

1 of 30 © Boardworks Ltd 2008

Topic 3 Water and Organic Molecules

CEB Textbook Chapter 2, pages 29-35 and

Chapter 3, pages 38 and 39.

Mastering Biology, Chapters 2 and 3


Learning Outcomes After studying this topic you should be able

to: •Draw the structure of a water molecule and

describe its polar nature.

•Explain what a hydrogen bond is and how they

contribute to the cohesion of water molecules.

•Explain how water acts as the solvent of life.

•Explain what is meant by the term “organic

molecules” (study notes). X You are not required to study the section How water moderates

temperature on page 30 of your CEB textbook nor the section Acids,

Bases and pH on page 32.


Structure of Water

Each hydrogen shares a pair of

electrons with the oxygen. The

oxygen has a greater affinity (stronger

pull) for electrons than the hydrogens,

so it ‘pulls’ the electrons closer.

Water (H2O) is a compound that consists of

two hydrogen atoms covalently bonded to one

oxygen atom.

δ+

δ+

104.5 °

δ–

This makes the oxygen slightly negative (indicated by δ–)

and the hydrogens slightly positive (indicated by δ+).

Because of its V shape (H’s on one side and O on the

other....

Water is a polar molecule = A molecule containing polar

covalent bonds (having opposite charges on opposite

ends). 4 of 30 © Boardworks Ltd 2008

Hydrogen Bonds Many of the properties of water are due to its ability to form

hydrogen bonds.

The slight negative charge on the oxygen atom makes it

attract the slightly positive hydrogen atom of another water

molecule.

hydrogen

bond

The numerous hydrogen bonds in water make it a very

stable structure.


Hydrogen Bonds Hold water molecules

together.

Each water molecule can

form a maximum of 4

hydrogen bonds

The hydrogen bonds

joining water molecules are

weak, about 1/20th as

strong as covalent bonds.

They form, break, and

reform with great frequency


Covalent bonding vs. Hydrogen bonding

Covalent Bond

Hydrogen Bond

2




Extraordinary Properties that are a result of

hydrogen bonds.

1. Cohesive behavior

2. Resists changes in temperature

3. High heat of vaporization

4. Expands when it freezes

5. Universal solvent

Hydrogen Bonds - Effects


1. Cohesion-tension theory Water is a polar molecule, meaning

that its positive and negative charges are

not evenly distributed.

This means that, in a thin tube (such as

a plant vessel), water molecules

spontaneously arrange so that positive

and negatively charged poles lie next

to each other

This causes the molecules to cohere, or

stick together by hydrogen bonding, so

that as some leave a plant by

evaporation (leaves), others are pulled

up behind them.


Cohesion = The attraction between molecules of the same

kind e.g. Water molecules by hydrogen bonding

Organisms Depend on

Cohesion! Cohesion among water

molecules plays a key role in the

transport of water against

gravity in plants

Adhesion, clinging

of one substance to

another, contributes

too, as water adheres

to the wall of the

vessels.


Capillary Action

Because water has both adhesive

and cohesive properties, capillary

action is present.

Capillary Action = Water is attracted to

another charged material e.g. glass by

adhesion and then through cohesion,

other water molecules move with it.

e.g. water in a straw

e.g. water moves through trees this way


Adhesion and Cohesion Cause Capillary

Action

Which gives water the ability to “climb” structures.

Why does the liquid climb higher in the thinner tube?


Adhesion Also Causes Water to …

Form spheres

& hold onto

plant leaves

Attach to a

silken spider

web

3




Activity!

Try to float a paperclip on water.

How is this possible?

What will happen if you touch the surface

with detergent?


VIDEOS – Surface Tension

http://www.youtube.com/watch?v=ynk4vJa-VaQ – Surface tension boat

http://www.youtube.com/watch?v=M6ypoyZRTkg – Jesus Christ Lizard

Surface Tension Surface tension, a measure of

the force necessary to stretch or

break the surface of a liquid, is

related to cohesion.

Water has a greater surface

tension than most other liquids

because hydrogen bonds

among surface water molecules

resist stretching or breaking the

surface


Water Molecules sticking to

themselves because they

are polar

Water doesn’t cling to Oxygen and Nitrogen in

Air


Activity! Making a surface tension speed boat.

1. Break a popsicle stick in half and place a small amount

of detergent on the end.

2. Place on a plate of water.

You only get one shot at this so enjoy

http://www.youtube.com/watch?v=Hm52rkh68JA


It takes much more

energy to raise the

temperature of water

compared to other

solvents. Why?

Because hydrogen

bonds hold the water

molecules together!

Water has a high specific

heat capacity.

2. Water Resists Changes in Temperature

Why is this

property

so

important

for life?


High Specific Heat Capacity

Water resists temperature

change, both for heating

and cooling.

Water can absorb or

release large amounts of

heat energy with little

change in actual

temperature.

High Specific

Heat Capacity =

Amount of heat

needed to raise

or lower 1g of a substance 1° C.

http://www.youtube.com/watch?v=ynk4vJa-VaQ



http://www.youtube.com/watch?v=M6ypoyZRTkg

4




3. High heat of vaporization

In order for water to

evaporate, hydrogen bonds

must be broken.

As water evaporates, it

removes a lot of heat with

it.

High Heat of

Vaporization =

Amount of energy

to convert 1g or a

substance from a

liquid to a gas


Effects of High Specific Heat Capacity

In late autumn / early winter, the temperatures near

the sea coast are usually higher because the

oceans are still releasing stored energy from the

summer.


In late fall / early winter, the temperatures

near the sea coast are usually higher

because the oceans are still releasing stored energy from the summer.


In late fall / early winter, the temperatures

near the sea coast are usually higher

because the oceans are still releasing

stored energy from the summer.


The high specific heat of water means that

a lake won’t freeze or heat up suddenly.

This gives aquatic organisms a chance to

adjust to temperature changes slowly.


Many people rely on the high specific heat

property of water to heat their home.

Water is warmed in the boiler and then

piped throughout the house before

returning.

5




4. Water Expands When it Freezes

As ice starts to melt, some

of the hydrogen bonds

break and some water

molecules can slip closer

together than they can

while in the ice state.

When water reaches

0oC, water becomes

locked into a crystalline

lattice with each

molecule bonded to the

maximum of four

partners.



Ice is about 10% less dense than water at 4oC.

Therefore it will float on water! (e.g. it has fewer

molecules of water per unit volume because of the

spacious crystal lattice structure)



The density of water:

1. Prevents water from freezing

from the bottom up.

2. Ice forms on the surface

first—the freezing of the

water releases heat to the

water below creating

insulation.

3. Makes transition between

season less abrupt.

Why is this

property so

important for

life?


5. Water is a Universal Solvent

Water is the solvent of Life!

Solute – substance dissolved

in a solvent to form a solution

Solvent – fluid that dissolves

solutes

Example: Ice Tea – water is

the solvent and tea and sugar

the solutes the result is a

aqueous solution

Why is this

property so

important for

life?


5. Water is a Universal Solvent

Water (solvent) can dissolve

many ionic solids e.g. salts,

sugars, because water

molecules are polar

The water molecules attach to

the ionic solids (solutes) due

to hydrogen bonding and pull

them into the solution

Can you think of some examples

in the body where this would be

important?

Why is this

property so

important for

life?


Water as a Solvent

6




Summary Quiz 1.Why is water a polar

molecule?

2.What is a hydrogen

bond?

3.What are the 5 life

supporting properties

of water?

4.The tendency of

water molecules of the

same kind to stick

together is called....


Properties and biological roles of water


Key words

Aqueous solution

Carbon skeletons

Cohesion

Digestion

Hydrocarbon

Hydrogen bond

Hydrolysis

Macromolecule

Monomer

Organic Molecule

Polar molecule

Polymer

Solute

Solution

Solvent

Synthesis


Homework 1.Complete handout question on water.

Due this Friday

2.Answer question 5 and 6 in unit

assessment 1

3. Read Study notes and DEFINE ‘organic

molecule’. Add to your glossary for the

topic

4.WATCH this video for excellent revision

of this topic

Recap –Water Liquid Awesome Video http://www.youtube.com/watch?v=HVT3Y3_gHGg

Or just search WATER LIQUID AWESOME on youtube!


• Which is polar, and which is non-polar?

Wax Paper = Non-Polar -/-

Water Droplets

Polar +/-


What did the molecules attach to? Why?

Answer: Because the water molecules are polar,

they attached to themselves and stayed in a

drop. The wax paper is non-polar, so the water

did not mix with it.

Water Droplets

http://www.youtube.com/watch?v=HVT3Y3_gHGg

7




Many products use polarity to help

waterproof materials.


Oil and Water don’t…________?

Add a few drops of vegetable oil to a clear Petri-

dish using an overhead projector.

What happens?

What happens when two oil bubbles meet?


Answer: When two (Non-polar) oil bubbles

meet, they join together to form a large

bubble.


Where have we seen the picture below?

54 of 30 © Boardworks Ltd 2008 55 of 30 © Boardworks Ltd 2008

Oil and water don’t mix. An oil spill can cause severe

damage to aquatic systems because of this property.

OIL IS WHAT WE CALL A HYDROCARBON

8



“Hydrocarbon Compounds”

Learning Outcomes

•Describe hydrocarbons and their

main function.

•Describe the synthesis and

digestion of polymers.

(C4H10)


Organic Chemistry and

Hydrocarbons

• “Organic” originally

referred to any chemicals that came from organisms

• 1828 - German chemist Friedrich Wohler synthesized urea in a lab

• Today, organic chemistry is the chemistry of virtually all compounds containing the element carbon


Friedrich

Wohler

1800 – 1882

Used inorganic

substances to

synthesize urea, a

carbon compound

found in urine.

This re-defined

organic chemistry.


Organic Chemistry and Hydrocarbons

• Over a million organic compounds, with a dazzling array of properties

• Why so many? Carbon’s unique bonding ability!

• Let’s start with the simplest of the organic compounds. These are the Hydrocarbons



• Hydrocarbons contain

only two elements:

1) Hydrogen, and

2) Carbon

• The simplest

hydrocarbons are called

“alkanes”, which contain

only carbon to carbon

single covalent bonds

(CnH2n+2)

• Methane (CH4) with one

carbon is the simplest

alkane. It is the major

component of natural gas 61 of 30 © Boardworks Ltd 2008


• Carbon has 4 valence

electrons, thus forms 4

covalent bonds

not only with other

elements, but also

forms bonds WITH

ITSELF (nonpolar)

• Ethane (C2H6) is the

simplest alkane with a

carbon to carbon bond

9




Hydrocarbons

• Many hydrocarbons

used for fuels:

methane, propane,

butane, octane

• As the number of

carbons increases, so

does the boiling and

melting pt. e.g.The first

4 are gases; #5-15 are

liquids; higher alkanes

are solids


Hydrocarbon - Alkanes

Since the electrons are shared equally,

the molecule is nonpolar thus, not

attracted to water oil (a hydrocarbon)

not soluble in H2O “like dissolves like”


Hydrocarbons - Natural Gas

• Fossil fuels (hydrocarbons)

provide much of the world’s

energy

• Natural gas and petroleum

contain mostly the aliphatic

(or straight-chain)

hydrocarbons – formed

from marine life buried in

sediment of the oceans


Coal

• Formed from huge

fern trees and

mosses decaying

millions of years ago

under great pressure

of rocks / soil.

• Coal may be found

close to the surface

(strip-mined), or

deep within the earth

• Pollutants from coal

are common; soot

and sulfur problems


BIG BRUTUS

Dragline used

to remove the

overburden of a

strip mining coal

field near West

Mineral, Kansas.

Note the size of

the man standing

next to it.


VIDEO - Formation of Polymers

Polymerisation 4.37

http://www.youtube.com/watch?v=UNsNGV

SVDMk

http://www.youtube.com/watch?v=UNsNGVSVDMk

http://www.youtube.com/watch?v=UNsNGVSVDMk

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