The periodic table shows all the elements





Elements, substances and materials

What is the difference between elements and atoms? or between molecules, substances and materials?

Everything we see on the Earth, and on the Universe as a whole, is made of 92 elements combined together (actually there are more than 92, as you can see on the table,but elements number 93 and above are man made and only tiny amounts exist). In the past chemists believed that everything was made out of earth, water and fire, but at present we know that this is not true.

Different elements can combine in different proportions and form various different molecules. For instance, we can combine hydrogen and oxygen (two gases at room temperature) to form water, a substance that is fundamental to all life forms.

Not all combinations of elements are possible. Chemistry is about determining how elements combine and why. We will learn a few simple rules - like the octet - that will allow us to predict chemistry in various situations.

Atoms and elements

The word atom comes from the Greek (a- means no; tom- means division). Hence, atom means indivisible (more on Greek and Latin words in science). You can break molecules into smaller molecules, or even into atoms. If you brake the toms, however, it loses its character.

Splitting atoms is in the domain of nuclear physics and the energies involver are much higher. In chemistry, all the processes studied involve only electrons. The nuclei of the atoms always remain intact.

The periodic table shows all different elements, or atoms. Each element corresponds to an atom, characterized by its atomic number.

In summary, element is normally used when talking about the periodic table, and chemistry in general. Atom is more used in physics. It is also used in chemistry when talking about atomic number or mass.

Molecules and substances

Substances consist of molecules or ionic compounds.

Molecules and ionic compounds are made of atoms joined together, by chemical bonds.

All substances consist of molecules or ionic compounds. Molecular compounds,for instance, include water, acetone, petrol, jet fuel, etc...


A material is formed of a large number of molecules. For instance, ice is a solid material formed with water molecules arranged in a tri dimensional array. An ice cube has a huge number of water molecules.

We can compare the formation of materials to the more familiar formation of words and text from letters:


letters - elements

word - substances

sentence - material

text - object

Leters are the basic entities, which get together to form a very useful product, which is the text. Text can convey information, messages, feelings, etc...

An object corresponds to text. Object is the ultimate use of the elements. For instance, a carrier bag is an object, made of the material polythene, which comprises billions of polythene molecules, each one of those formed by atoms of carbon and hydrogen.


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