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Importance of Water

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Water (H2O) is a chemical compound (A substance formed by the chemical combination of two or more elements in definite proportions-meaning they are happy). The water molecule (smallest unit of most compounds) contains two atoms (basic unit of matter) of hydrogen for each atom of oxygen. Hydrogen and Oxygen are two different elements (pure substances that cannot be broken down to simpler means that consist entirely of one atom). Atoms like hydrogen and oxygen atoms are made up of subatomic particles called protons (positively charged particles in the nucleus (bond between protons and neutrons in the center an atom) of an atom), neutrons (particles with no charge located in the nucleus of an atom), and electrons (negatively charged atoms surrounding the atom in shells, or rings). So going back to the water molecule, which is H2O, the hydrogen atom (as seen on the periodic table) has 1 proton and one electron. Every atom has valence electrons which are electrons situated on the outermost shell of an atom. However, these shells have rules. The first shell can only hold up no more than 2 electrons, so if an atom has only two electrons in the whole atom, the atom is “happy” or balanced. Now, when an atom has more than two electrons, like the oxygen atom, which has 8, it will move on to the next shell which can hold up to 8 more electrons. So in the oxygen atom case, it will have 6 electrons in the outermost (2nd shell). The next one which is the third shell can hold up to 18 valence electrons. The last shell is the fourth one which holds 32 valence electrons and there isn’t any atom that can exceed the third valence shell so it is thought to be the final valence shell there is. So, atoms in compounds are held together by chemical bonds. Why? Well atoms bond when their valence shell is not full meaning they are unbalanced and they need to bond in order to fill each other’s valence shells to become balanced and stable. When an atom has (a different number of electrons than it should) have, it is called an ion. On the other hand, an isotope is (an atom that differs in the number of neutrons it contains) but in this compound, no isotopes are seen. Now, the compound H2O is held together by a covalent bond (a bond where electrons are shared between atoms). A covalent bond shares the electrons meaning that instead of having electrons transferred as in the ionic bond (a bond when atoms are transferred from one atom to another), electrons are located in a region where the orbitals of the atoms overlap each other. For example, a covalent bond would occur when when an atom is in need of the same thing that is offered by the other atom which completes both atoms valence shells making both atoms again “happy”. So this can exactly be seen in the water compound H2O. Oxygen has 6 valence electrons in its second shell and in order to be happy it needs two. Now hydrogen has only one valence electron in total and for it to be happy, it needs just one more where oxygen needs two. SO, that is why there are two hydrogen atoms shared with oxygen so that oxygen has TWO more valence electrons to complete its shell and the two separate hydrogen atoms complete their own shells as well by the sharing of the valence electrons. Now if there are a couple of water (or any type of) molecules closeby, van der Walls (a slight attraction between small oppositely charged regions of nearby molecules) forces can take place. But how? So, for the water molecule, because of the bent shape, the oxygen atom is on one end of the molecule and the hydrogen atoms on the other. Due to this, the oxygen end will have more of a slight negative charge and the hydrogen end, a slight positive charge. Because of these distributed regions of slight positive and negative charges, these polar molecules can attract to each other. The attraction between hydrogen on one molecule and oxygen on the other is called a hydrogen bond. Now because of this hydrogen bonding, water is extremely cohesive. Cohesion (an attraction in the same atoms between molecules) causes molecules at the brim of the water to be pulled inward which is how tiny water beads are formed. Also, this cohesion is the reason why some insects and spiders can walk on top of water without sinking so it affects them greatly. Now adhesion (an attraction between molecules with different atoms) is the reason why the water surface slightly dips at the tip of a graduated cylinder. The adhesion between the water and glass molecules is stronger than the cohesion between just the water molecules. Together cohesion and adhesion make up for one of the the most important factors to plant life. Capillary



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