What is an Atom?
Don’t you find it amazing how everything you interact with is made of the same tiny building blocks? The computer you’re using, the coffee cup, the coffee! Yet each item has a different appearance and different properties, defined by the type of element or molecule involved.
The atom
The building block of chemistry, an atom is made up of three smaller components – protons, neutrons and electrons.
An atom consists of a ‘core’ known as a nucleus which contains the protons and neutrons. This is surrounded by a cloud of electrons which are attracted to the nucleus by electromagnetic forces. Protons and electrons are charged particles, with protons carrying a +1 charge and electrons carrying a -1 charge. In order for an atom to be neutral the number of protons and electrons must be equal. If the numbers of protons and electrons are not equal the atom carries either a positive or negative charge and becomes an ion.
An atom of carbon is shown in the periodic table like this:
6
C
12
The top number is the atomic number and the bottom number is the atomic mass. From these numbers we know how many protons, neutrons and electrons one atom of carbon contains.
The atomic number is the number of protons, and therefore the number of electrons; as all atoms are neutral so they must balance out. The atomic mass is the overall mass of the atom’s densely packed nucleus, in this case 12. So we can calculate the number of neutrons because we know there are only protons and neutrons in the nucleus and we know the atomic mass.
Therefore the number of neutrons is the atomic mass minus the atomic number, which for carbon is:
12 (atomic mass) – 6 ( number of protons) = 6 (number of neutrons)
The size of an atom varies depending upon the element. If you have a look at the periodic table you will see every element has a different atomic mass and a different atomic number. This means every element has a different number of electrons, protons and neutrons and that is the reason each element is unique.
Negatively charged electrons are constantly orbiting an atom’s positively charged nucleus, due to attraction between the charges. Electrons are arranged into ‘shells’, with each shell containing a certain number of electrons. The first shell around a nucleus can hold 2 electrons, the second shell can hold 8 electrons and so on. An atom is only happy when it has a complete shell, whether its the first shell with 2 electrons or the second shell with 8 electrons. For example, oxygen has an atomic number of 8. This means there are 8 electrons in every oxygen atom. 2 of these electrons live in the first shell, the other 6 live in the second shell. As the second shell needs 2 more electrons to be complete, oxygen is an ‘unhappy’ atom.
Water has probably the most well known chemical formula, H2O. This means it is made up of 2 atoms of hydrogen and 1 atom of oxygen. A hydrogen atom has only 1 electron and so needs 1 more electron to complete its first (outer) shell. By sharing one electron from each hydrogen atom with the oxygen atom the oxygen atom can complete its second (outer) shell and all the atoms become ‘happy’. However, as water is made up of more than one atom it is now called a molecule.
So now, every time you make a drink or take a shower you can amaze at how something so small can make such a difference to our everyday lives.