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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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    By: Jojo
    Date: Jan 05, 2016

    I like the way you explain the importance of water!

    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

    By: Lufikile
    Date: Aug 27, 2015

    Its good it explains everything clearly

    By: lindsay
    Date: Aug 22, 2015

    quite good though a little general

    By: markuss
    Date: Mar 30, 2015

    i love it sooooooo interesting

    By: tathan
    Date: Dec 17, 2014

    thanks very helpful

    By: Chris Preziotti
    Date: Dec 06, 2014

    I would like t know who the author of this article is because I am using this as a source for a science project and we are required to cite our sources.

    {HST adds:
    Here is the format of a typical online citation when the author is not named:

    “Article name.” Site name. Date Accessed <web address>.

    An example:

    “What is the Scientific Method?” Home Science Tools. Accessed 21 September 2012

    Hope this helps!}

    By: choolwe simafuta
    Date: Nov 01, 2014

    so helpful. thanks

    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?