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    Home / Science lessons / Properties of Water
    • Properties of Water

      Properties of Water

      One of the things that makes our planet special is the presence of liquid water. Water is fundamental for all life; without it every living thing would die. It covers about 70% of Earth's surface and it makes up 65-75% of our bodies (82% of our blood is water). Even though water seems boring - no color, taste, or smell - it has amazing properties that make it necessary for supporting life.

      The chemical composition of water is H2O - two hydrogen atoms and one oxygen atom. Water has special properties because of the way these atoms bond together to form a water molecule, and the way the molecules interact with each other.

      Water molecules line up positive end to negative end

      When the two hydrogen atoms bond with the oxygen, they attach to the top of the molecule rather like Mickey Mouse ears. This molecular structure gives the water molecule polarity, or a lopsided electrical charge that attracts other atoms. The end of the molecule with the two hydrogen atoms is positively charged. The other end, with the oxygen, is negatively charged. Just like in a magnet, where north poles are attracted to south poles ('opposites attract'), the positive end of the water molecule will connect with the negative end of other molecules.

      What does this mean for us? Water's polarity allows it to dissolve other polar substances very easily. When a polar substance is put in water, the positive ends of its molecules are attracted to the negative ends of the water molecules, and vice versa. The attractions cause the molecules of the new substance to be mixed uniformly with the water molecules. Water dissolves more substances than any other liquid - even the strongest acid! Because of this, it is often called the 'universal solvent.' The dissolving power of water is very important for life on Earth. Wherever water goes, it carries dissolved chemicals, minerals, and nutrients that are used to support living things.

      Because of their polarity, water molecules are strongly attracted to one another, which gives water a high surface tension. The molecules at the surface of the water "stick together" to form a type of 'skin' on the water, strong enough to support very light objects. Insects that walk on water are taking advantage of this surface tension. Surface tension causes water to clump in drops rather than spreading out in a thin layer. It also allows water to move through plant roots and stems and the smallest blood vessels in your body - as one molecule moves up the tree root or through the capillary, it 'pulls' the others with it.

      Water is the only natural substance that can exist in all three states of matter - solid, liquid, and gas - at the temperatures normally found on Earth. Many other substances have to be super-heated or -cooled to change states. The gaseous state of water is present continually in our atmosphere as water vapor. The liquid state is found everywhere in rivers, lakes, and oceans. The solid state of water, ice, is unique. Most liquids contract as they are cooled, because the molecules move slower and have less energy to resist attraction to each other. When they freeze into solids they form tightly-packed crystals that are much denser than the liquid was originally. Water doesn't act this way. When it freezes, it expands: the molecules line up to form a very 'open' crystalline structure that is less dense than liquid water. This is why ice floats. And it's a good thing it does! If water acted like most other liquids, lakes and rivers would freeze solid and all life in them would die.

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    Comments




    By: Memory Magoche
    Date: Sep 16, 2017

    Well explained I really understood the science behind the water molecule.


    By: Ahmed
    Date: Sep 14, 2017

    we should focus on the unique properties of water and how they support life.  and hence 70 percent on earth is water we need to improve our knowledge towards water.


    By: Charlize
    Date: May 24, 2016

    Dear Akol Chan,
        It’s call gravity. And because the air is less dense than the water so the air is on top. Air is 100% oxygen, but water is only 88.9% oxygen.


    By: Charlize
    Date: May 24, 2016

    Actually Christopher, it said nothing about the water cycle. The water cycle is from Evaporation of water from the ocean or rivers rise and condense to form clouds which then transport elsewhere until precipitation occurs. It then goes along the surface as runoff or is absorbed into the ground, turning into groundwater. Then it finds it’s way back to rivers and oceans or ends up back into the atmosphere through transpiration. And that my friend is the Hydrologic cycle.


    By: Robert Allen Gerald
    Date: Feb 29, 2016

    Re: By: Akol Chan
    Date: Aug 03, 2014
    when a container is half- filled with water, there is a space on the top of the container. But when ones places that container flat, the space moves from top contain side (at back). What makes water to behave in that particular way?

    This is an incomplete question.  From what I what I am reading and using my presumptive ways. I will reword and try to answer this question.

    OK this is what it sounds like they are asking. :
     
    Q:  If you hold a glass at an angle, fill it half way up with water, set said glass on a level surface. Upon which the water finds itself imediatly collecting at the bottom most point of the glass becoming level why dose this occur? 

    A:  This sounds to me that this is caused by mass. When an object has mass it effects and is effected by other objects with mass. This attraction is known as gravity. It works to cause the surface tension, which holds the water together. Without it water would fall up and disapate flowing out of the cup like feathers out of a pillow in a pillow fight. So the mass of the water is holding itself together and the mass of the earth holds it down in the bottom of the glass.

    Now due to the question the asker might have been wondering about the meniscus, that is what you call the curved surface when the water is in a glass or tube and the surface tension appears to curve at the surface.  I believe that is caused by both the surface tension and the capulary effect where a waters surface tension holds its self together yet spreds it out even elevating it even against gravity.


    By: Jojo
    Date: Jan 05, 2016

    I like the way you explain the importance of water!


    By: Clinton Bashore
    Date: Dec 16, 2015

    Because of the electrical polarity water molecules are attracted to each other causing clumping. Water can carry oxygen but clumping reduces the oxygen carrying capacity. Is any information available?


    By: Clinton Bashore
    Date: Dec 16, 2015

    I was looking for the clumping property information of water. I understand that are at least 8 different kinds of water and 11 different kinds of ice due to this feature.


    By: Christopher
    Date: Nov 07, 2015

    This website was really helpful because it told me a lot of information about
    water cycle and the properties of water :)


    By: nicole
    Date: Nov 03, 2015

    awesome lessons and experiments to teach to my students