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Water. Water is the most essential and abundant substance on Earth. Cells are made up mostly of water and most cells are surrounded by water. The importance of water is largely due to its many unique characteristics, which all directly relate to one very important property of water.

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water
Water

Water is the most essential and abundant substance on Earth. Cells are made up mostly of water and most cells are surrounded by water. The importance of water is largely due to its many unique characteristics, which all directly relate to one very important property of water.

slide2

What is that very important property if water????

Water is……..

_______________

Polar!!!

Polarity is the unequal sharing of electrons in molecules formed with covalent bonds

remember what type of bond forms a water molecule covalent

The chemical formula of water is ___________. The atomic number of hydrogen is ___ and the atomic number of oxygen is ___.

Therefore how many protons does the oxygen nucleus have?

How many protons does each hydrogen nucleus have?

Due to this difference, the oxygen nucleus has a much stronger positive charge than each hydrogen nucleus.

Remember…

What type of bond forms a water molecule???

Covalent!

slide4
Because the oxygen nucleus has a much stronger positive charge than the hydrogen…

the shared negatively-charged electrons are much more attracted to oxygen (because of its greater positive charge).

This results in all 10 electrons

orbiting around the oxygen end

of the molecule just about all the

time.

slide5
Because of the shape of a water molecule (bent), oxygen is at one end while the hydrogen atoms are at the other.

Therefore, the oxygen end of the molecule is slightly negative (due to the presence of all those electrons) and the hydrogen end of the molecule is slightly positive (due to the lack of the electrons).

A molecule in which the charges are unevenly distributed is called a polar molecule, because the molecule is like a magnet with poles.

slide6

HYDROGEN BONDS

Bonds that form between the_________ charged _____________

in one molecule and a

__________ charged _________

in a nearby molecule are called

_____________________

positively

HYDROGEN atom

negatively

atom

HYDROGEN BONDS

Is a hydrogen bond a true chemical bond?

No- it does not result in the formation of a new compound- it is simply an attraction.

Hydrogen bond animation

Images from: http://www.estrellamountain.edu/faculty/farabee/biobk/BioBookCHEM2.html

slide7
Because of their partial positive and negative charges, polar molecules such as water can attract each other

The attraction between the Hydrogen atom on one water molecule and the oxygen atom on the other water molecule is an example of a hydrogen bond.

slide8
but it is water’s ability to form

________________________

that is responsible for many of its special properties and characteristics.

Hydrogen bonds are not as strong as covalent or ionic bonds…

Multiple hydrogen bonds

A single water molecule may be involved with as many as ___ hydrogen bonds at the same time.

4

slide9

Properties of waterDue to water’s polarity, it has unique properties important in maintaining that forever important internal harmony we call… (everyone together!!!)

1. Water is “sticky”

Cohesion

Adhesion

Surface Tension

2. High specific heat

3. High heat of vaporization

4. Expansion on freezing

5. Water as a Solvent

cohesion
Cohesion

“Co” = “together” or “like”

“sion” = “stick”

The attraction between molecules of the same substance (why droplets of water form)

Due to formation of multiple hydrogen bonds

Contributes to the upward transport of water in plants- capillary action (roots  shoots)

adhesion
Adhesion

“Ad” = “unlike”

The attraction between molecules of different substances

Due to formation of multiple hydrogen bonds between polar water molecules and other slightly charged molecules

water on a penny; along with cohesion, contributes to capillary action (the ability of water to rise in a narrow tube against the force of gravity)

surface tension
Surface Tension

The measure of how difficult it is to stretch or break the surface of a liquid

Results from the H bonding of water molecules to one another at the surface and below the surface (cohesion)

Gives still water on a lake or pond the appearance of glass

Ex: insects walking on water

high specific heat
High Specific Heat

The amount of heat needed to raise the temp of 1 gram of water by 1 degree Celsius

Water has a very high specific heat- it takes a lot of energy to raise the temp of water

Crucial in temperature stability in living systems so that they can maintain homeostasis

Due to H bonding

high heat of vaporization
High Heat of Vaporization

A lot of heat energy is required to evaporate water (molecules that move fast enough can overcome their attraction to one another and depart the liquid and enter the air as gas)

When water does evaporate from a surface, it draws heat energy out from the layer beneath, creating a cooling effect.

This is called evaporative cooling

Ex: evaporation of sweat by a human; evaporation of water from leaves of plant (transpiration)

ice floats expansion on freezing
Ice Floats (Expansion on Freezing)

Water is one of the few substances that are less dense as a solid than as a liquid- therefore it floats.

While other materials contract when they solidify, water expands.

expansion on freezing cont d
Expansion on Freezing cont’d
  • Water begins to freeze when its molecules are no longer moving fast enough to break their H bonds. As the temp reaches 0 degrees C, the water becomes locked into a crystalline lattice, with each water molecule bonded to the max of 4 other water molecules.
  • Due to H bonding- keeps the

molecules at “arms length”-

far enough apart to make ice

10% less dense than liquid water.

(water’s density= 1.0 g/ml)

water as a solvent
Water as a Solvent

Water dissolves many substances due to its polarity.

Known as a very versatile solvent- other polar substances dissolve very easily in water.

slide18
Solution- a completely homogeneous mixture of 2 or more substances

Solvent- the dissolving agent

of a solution. Ex. Water

Solute- the substance that is

being dissolved

slide19

“Like dissolves like”

HYDROPHILIC

____________________ means “water loving”

_________ groups/molecules try to _________ and touch water or ______________ molecules

POLAR

be near

other polar

Water makes a great solvent in

living things because so many

molecules found in living things

are polar or have a charge.

http://www.makash.ac.il/h_school/hst/hstsb/chem/luach/dissolve.jpg

slide20

http://egullet.com/imgs/egci/nonstocksauce/nons1.JPG

“Like dissolves like”

HYDROPHOBIC

_________________ means “water fearing”

___________ groups/molecules try to _________ other __________ molecules and __________ ________ molecules

NON-polar

be near

NON-polar

polar

away from

Oil based paints dissolve

in solvents such as

turpentine

. . . not water.

slide21
Examples of hydrophilic substances- salts, polar compounds (sugar)

*Also known as water soluble

Examples of hydrophobic substances- oils, fats, lipids, waxes (non-polar compounds)

*Also known as water insoluble

slide22

http://mchi.mcallenisd.org/mchi/site/hosting/ipc/ipc/ipcch23htm/ipcch23sec2.htmhttp://mchi.mcallenisd.org/mchi/site/hosting/ipc/ipc/ipcch23htm/ipcch23sec2.htm

“Like

dissolves

like”

SOAP

______ works because it has a _____________ that dissolves _______ and a __________ that dissolves in _____ to wash away oily dirt.

grease

NON-polar end

Polar end

water

slide23

WATER is important for all living things

Average person ~~ 60-70% water

Babies ~~ 78%

Human brain ~~90%

Image from: http://sjr.state.fl.us/programs/outreach/pubs/irl_update/images/water_glass.jpg

why water is important to cells
WHY Water is important to cells:

1. It’s __________ so it can ____________ lots of different substances.

2. It can _________ lots of ______

_______________________________ very much. (That helps with _________________)

3. ____________________ form between water

molecules so they stick together.

4.Water is an important ___________________

in many CHEMICAL REACTIONS.

POLAR

DISSOLVE

absorb

HEAT

WITHOUT changing temperature

HOMEOSTASIS

HYDROGEN BONDS

REACTANT/PRODUCT

ad