Definition of Element

What is an Element?

An element is a substance whose atoms all have the same number of protons: another way of saying this is that all of a particular element's atoms have the same atomic number.

Elements are chemically the simplest substances and hence cannot be broken down using chemical reactions. 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.

How Elements Came to be Defined Correctly

In 1913, chemistry and physics were topsy-turvy. Some big hitters - including Dmitri Mendeleev - were talking seriously about elements lighter than hydrogen and elements between hydrogen and helium. Visualizing the atom was a free-for-all, and Mendeleev's justification for a periodic table based on the elements' atomic weights was falling apart at the seams.

This is the story of how Henry Moseley brought light to the darkness.

The Most Abundant Elements

With only one proton, hydrogen is the simplest, lightest element, followed by helium, which has two protons. Oxygen atoms have eight protons.

At 75 percent, hydrogen is the most abundant element in the universe, followed by helium at 23 percent, then oxygen at 1 percent. 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 118 accepted elements.

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: this was the year Hennig Brand became the first known person to discover a new element - phosphorus.

Combining Elements
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 chemically bonded to one of oxygen.

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