Matter: Atoms


Atoms are the basic building blocks of matter. From a drop of water, to a coin, to a live animal, these teeny particles are the most basic unit of any element. You cannot see atoms unless you use a special microscope. Atoms contain three tiny particles: protons, neutrons, and electrons.

Protons and neutrons are packed into an extremely dense region in the center of an atom called the nucleus. Protons have a positive (+1) charge, and neutrons are neutral, having no charge (0).

Electrons are found outside the nucleus, orbiting throughout the atom's empty space. Electrons have a negative (-1) charge. Electrons are much smaller than protons and neutrons, and numerous electrons form an electron cloud around an atom.


An element is a substance who's atoms have the same number of protons in the nucleus. Atoms of the same element can have a different number of neutrons (called isotopes), since neutrons have no charge. Elements are the simplest substance that cannot be broken down further into smaller, different units because they contain the same type of atom.

There are currently 118 known elements scientists have discovered. They are organized on the Periodic Table of Elements by number of protons.

There are a limited number of elements available on Earth. We cannot just produce more of an element, because elements, like everything around us, is matter. The elements in the air we breathe, in the Earth's crust, in the atmosphere - are all limited, even if they seem abundant.

Chemical Symbols

Every element in the Periodic Table is represented by a one or two-letter abbreviation called a chemical symbol. The first letter of the symbol is capitalized. Examples include C for carbon, Fe for iron, and Br for bromine. Chemical symbols are like a code name for the element. These short representations are used especially when writing chemical formulas for compounds.


A chemical compound is a substance that is composed of at least two atoms of different elements. The atoms of a compound are held together by a chemical bond. Compounds are represented by chemical formulas.

Chemical Formulas

A chemical formula is a way of representing the proportions and number of atoms of different elements that make up a chemical compound. Chemical formulas are written using the chemical symbol of each element. The number of atoms of a particular element in a compound is denoted by a subscript to the right of the element symbol, except when there is only one atom of that element. More complicated chemical formulas may contain parentheses around special groups of atoms, plus-minus signs, and more.

Chemical Equations

Chemical equations are used to model chemical reactions that are taking place. In a chemical reaction, elements are rearranged. To show that a reaction is taking place, chemical equations use the arrow (-->) symbol. The compounds on the left side of a chemical equation are known as reactants, whereas the compounds on the right are called the products.

Coefficients in front of certain reactants and products indicate the amount of that compound used up or produced in the reaction. Chemical equations are always balanced, meaning that the number of each type of atom in the products and reactants is the same.

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