Atoms and the Periodic Table

Atoms and elements

All substances on earth are made up of atoms. Atoms are the smallest part of elements that exist. At present there are more than 100 different elements, all of which are shown on the periodic table. Although more elements are discovered all the time and in 2015 four new elements were added to the Periodic table (Tennessine, Nihonium, Moscovium and Oganesson).

The diagram below is the Periodic Table.

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Atoms of each element are represented by a chemical symbol in the periodic table. For 1 letter elements the letter is always shown in uppercase, for 2 letter elements the first letter is shown in uppercase and the second letter is always shown in lowercase.

Elements, compounds and mixtures

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Elements contain only one type of atom and consist of single atoms or atoms bonded together.

Compounds contain two (or more) elements that are chemically combined in fixed proportions.

Mixtures contain two or more elements (or compounds) that are together but not chemically combined.

The video below explains elements, compounds and mixtures.

Chemical Equations

Words or symbol equations can be used to represent chemical reactions.

Word equation: Copper + Oxygen = Copper Oxide

Chemical equation: Cu + O₂ → CuO

Glossary of terms

Atom: The smallest part of an element that can enter into a chemical reaction.

Element: A substance that consists of only one type of atom.

Compound: A substance consisting of two or more elements chemically combined together.

Mixture: Two or more elements or compounds that are not chemically combined.