What is an Element?
An element is a substance consisting of atoms which all have the same number of protons - i.e. the same atomic number.
Elements are chemically the simplest substances and hence cannot be broken down using chemical methods. Elements can only be changed into other elements using nuclear methods.
Although an element's atoms must all have the same number of protons, they can have different numbers of neutrons and hence different masses. When atoms of the same element have different numbers of neutrons, they are called isotopes.
The Most Abundant Elements
With only one proton, hydrogen is the simplest, lightest element, followed by helium, which has two protons.
At 75 percent, hydrogen is also the most abundant element in the universe, followed again by helium at 23 percent, then oxygen at 1 percent. Each oxygen atom has eight protons. All of the other elements make up the remaining 1 percent.
In the earth's crust, oxygen (47 %) is the most abundant element, followed by silicon (28 %) and aluminum (8 %).
Element Names and Numbers
All of the elements have been named. Some of these names are familiar to us, such as nitrogen and sodium, and some are less familiar, such as dysprosium and roentgenium.
We can also name elements using their atomic numbers. For example, element 1 is hydrogen, element 2 is helium, element 3 is lithium, element 8 is oxygen, etc.
How Many Elements Are There?
There are currently 115 accepted elements and three elements whose existence has been claimed, but not yet accepted (elements 113, 115 and 118).
We use the periodic table to display all of the elements in an organized way.
Elements Ancient and Modern
Some elements have been known for thousands of years, and we do not know who discovered them. These are: antimony, arsenic, carbon, copper, iron, gold, lead, mercury, silver, sulfur, and tin.
All other elements have been discovered since 1669; it was in this year that Hennig Brand became the first named person to discover a new element - phosphorus.
An element can combine with one or more other elements to form compounds, of which there are millions. For example, one of the best-known compounds is water, written chemically as H20, which means that water is made of two atoms of hydrogen combined with one of oxygen.