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Atoms, elements and compounds

Atoms, elements and compounds

In this chapter you will learn:

  1. What are Atoms?

  2. What are Elements?

  3. What are Compounds?


All substances are made up of atoms.

Atoms are the smallest part of an element that can exist.

Atoms themselves are made from three types of small particles, called: protons, neutrons and electrons.

Nucleus is in the center of the atom and contains protons and neutrons. The electrons move around the nucleus in orbits called shells.


An element is a substance containing one type of atoms.

Each element has its own chemical symbol. A chemical symbol contains one or two letters and starts with a capital letter. For example, the symbol "O" represents an atom of oxygen, and "Na" represents an atom of sodium.

There are more than 100 different elements. The elements are listed in the periodic table.

The number of protons in an atom of element is called the atomic number. Atoms contain equal numbers of protons and electrons.

Atomic numbers are used in Periodic Table to arrange the elements.


Compound contains two or more elements that are chemically combined. Compounds are formed from elements by chemical reactions.

Chemical reactions always involve the formation of one or more new substances. Most chemical reactions involve a detectable energy change. Compounds have different properties from the elements they are made from.

It is too hard to split up a compound into its elements.

Compounds can be spilt up into elements by chemical reactions.