Introduction to elements
What is an element?
An element is a substance made up of one type of atom. Chemists classify atoms by the number of protons they possess, represented by an atomic number. Atoms with the same atomic number are of the same element, therefore all atoms of one element have the same number of protons. See animation 1.
The chemical symbol of an element is a letter, or combination of letters, representing the element. Generally, the chemical symbol for an element is taken from the first letter of the word form of the element, for example 'H' for hydrogen or 'O' for oxygen. If the letter has been taken, two letters are used, such as with 'He' for helium, where 'H' has been taken by hydrogen. The second letter of the chemical symbol is usually the second letter of the element's name, though occasionally the third letter might be used e.g. 'Cl' for chlorine.
The more obscure chemical symbols may not match the element's name, for example 'Na' for sodium or 'Pb' for lead. This is because these elements have a name that may come from other languages such as Latin or Greek. The Latin word for lead is 'plumbum', hence its symbol is 'Pb'.
Atoms and elements
Sometimes the word 'atom' and the word 'element' are interchanged depending on the context. To clarify the terminology between an atom and an element, it is necessary to consider atoms as chemical building blocks made of protons, neutrons and electrons and that the number of these particles varies. An element contains one type of atom, that is, atoms that all contain the same number of protons. See image 1 and image 2.
The word 'atom' and the word 'element' become interchangeable when referring to individual atoms in the same element, such as explaining a reaction.
Visualise the difference between cricket balls and tennis balls. They are different sizes and they have a different mass, but they are both still balls. Balls are the 'atoms' in this case whereas the type of ball is the element.
Isotopes
Atoms of the same element have the same number of protons as each other (and therefore the same number of electrons) but they can have different numbers of neutrons. An isotope is an atom with the same number of protons but a different number of neutrons from another atom of the same element. An isotope is a heavier form of the same element.
Isotopes are identified by their mass number. While all atoms of the same element will have the same atomic number, that is, the same number of protons, isotopes of that element will have the same atomic number but a different mass number. The mass of an atom is calculated by adding the number of protons with the number of neutrons. The negligible mass of electrons is not generally counted. See animation 2.
Different elements have different numbers of isotopes, some of which scientists create artificially.
