It is something that cannot be broken down into simpler materials or parts.
There are 118 known elements.
Their properties are: state in room temperature, how they combine with other elements, and if they are metals, nonmetals, or metalloids.

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​Elements

Metals - they are mostly shiny, conductive, and flexible (sodium, copper, gold)
Nonmetals - poor conductors, dull, and brittle (chlorine, oxygen)
Metalloids - have some properties of metals and nonmetals (silicon)

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​Kinds of Elements

If you keep cutting a piece of aluminum in half, you will reach a point where you cannot cut it any more.
The smallest particle of an element that retains its properties is called the atom.

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​The Atom

Atoms are made of particles.
These particles are the same for every type of atom.
Nucleus - made up of protons and neutrons.
Protons - have a positive charge, the number of protons is the atomic number.
Neutrons - no electric charge.
Electrons - have a negative charge, they move around the nucleus.

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​Parts of an Atom

When the mass of protons and neutrons in an atom are added up, you get the atomic mass.
*In Niels Bohr's model of the atom, the electrons orbit around the nucleus like planets. Now, we know that electrons act like a cloud of electric charge.

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​Atomic Mass

They are particles with more than one atom joined together.
Atoms link together with bonds of electrons.
Molecules are described using their chemical formulae.

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​Molecules

​Elements are represented by their symbols. The first letter is always capital (H, C, N, O, Mn, Li, Be)
Some elements like Au, Ag, Hg, or Pb are represented by their ancient names.

​The Periodic Table

In 1869, Dmitri Mendeleev made cards for all known elements. He ordered them from lightest to heaviest. He found that their properties repeat in cycles. This led to the creation of the periodic table.

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​The Periodic Table

The most common elements in space are H and He.
On Earth, the most common elements are H, O, Si, Al, N, Fe, and Ca.

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Most Common Elements