ATOMS, MOLECULES AND ELEMENTS

Link to weblesn notes.



This web lesson is about physical science.  In this case the science is chemistry.  All matter in the universe is composed of atoms.  There is also energy. Energy takes the form of radiation such as sunlight or gamma rays from other space.  All the solid things in the universe are made of atoms.   Although they are far to small to be seen, it has been established that atoms have a center called the nucleus and have small electrical particles called electrons orbiting the nucleus.  Here is an illustration:


The blue moving balls are electrons. They have a negative electrical charge.  The green and red balls in the center are the nucleus.  The green balls are called neutrons and have no electrical charge.  The red balls are called protons and have a positive electrical charge.  Atoms are characterized by their atomic weight.  The atomic weight of an atom may be thought of as the number of protons and neutrons in the nucleus of an atom.  For example, the element hydrogen has one proton in its nucleus and therefore has an atomic weight of 1.  The element helium has two protons and two neutrons in its nucleus and has an atomic weight of 4.  The number of protons in the nucleus of an atom is called the atomic number of thw atom.

There are about 100 known elements and each one has a different atomic weight.  Very often, the elements are shown in the periodic table. Here is a website showing the periodic table.  You can click on any element to find out more about it.

The atomic properties of the elements determine how atoms interact with each other.  Atoms interact with each other to form molecules.  The electrons of atoms orbit the nucleus in rings sort of like the rings around the planet Saturn:


SATURN 


When the innermost ring has 2 electrons, it is complete.  The outer rings may have up to 8 electrons.  The magic numbers for electron rings are 2 and 8. When a ring has 2 or 8 electrons, it is 'satisfied' and doesn't try to get or get rid of any more electrons.  When a ring does not have a magic number of electrons, it tries to borrow or loan some electrons from or to other atoms.  When it does this, the atom forms a bond with another atom.  There are reasons for those magic numbers 2 and 8 and someday you may study them in a subject called quantum mechanics.

Lets look at a simple molecule, water.  A water molecule is made of two hydrogen atoms and one oxygen atom.  The chemical symbol for water is H2O.  It means two hydrogen atoms and one oxygen atom make one water molecule.  The oxygen atom has 6 electrons in its outer ring and each of the hydrogen atoms have 1.  So the hydrogen atoms 'loan' the oxygen atom 1 electron each.  When they do, they stick to the oxygen atom and become water.  The oxygen atom is now happy because it has 8 electrons and the hydrogen atoms are happy to share.  Here is a diagram of the situation:


At the start (Before), the oxygen atom in the middle has 6 electrons (red).  The two hydrogen atoms each have 1 electron (blue).  The hydrogens react with the oxygen and each shares an electron.  The result (After), is a water molecule.

Actually, oxygen and hydrogen are not commonly found in their atomic state.  In nature, they are found as molecules so the actual formation of water is something like this:


 



 

How atoms combine to make molecules is the science of chemistry.  There are many thousands of chemical compounds made by reactions similar to that shown above for water.

To visit a website about about atoms and molecules click here or here.

Metals constitute an important group of elements.  Click here to read about metals.