 In this video, we will be talking about elements, molecules, and compounds. A pure substance is a substance that consists of only one type of particle. With a pure substance, the properties of that substance are the same no matter how much of the substance you have. For example, a teaspoon of water and a gallon of water both have the same chemical and physical properties. There are two main types of pure substances, elements and compounds. An element is a pure substance that is made of only one type of atom. An atom of an element is the smallest part of an element that still has the properties of that element. Atoms cannot be broken down into smaller substances by any chemical reaction. It would take a nuclear reaction to do that. That is atom splitting. If you were to break an atom down, you would change the identity of the atom to one of another element. Many elements exist as single atoms, but some elements exist as two or more of the same type of atom attached to each other by chemical bonds. A chemical bond is an attractive force that holds atoms together. A molecule is a particle that is made of two or more atoms that are held together by covalent bonds, and we'll learn more about these later. In nature, some elements like oxygen are most commonly found as molecules. This picture shows examples of some common elements that typically exist as molecules. Even though these particles are bound together by chemical bonds, they are considered to be elements because there is only one type of atom in the molecule. There are other molecules that are made up of two or more different elements. The atoms in the compound are bound so strongly that the compound behaves like one substance. It has very different properties than the atoms that formed it do. For example, water is made of two hydrogen atoms and one oxygen atom. The two hydrogen atoms are made up of two hydrogen atoms and one hydrogen atom. But the properties of water are very different from the properties of hydrogen and oxygen, which are usually gases. Sodium chloride, also known as table salt, is made of sodium and chlorine atoms. However, it has very different properties from sodium, which is a soft silver, very reactive metal, and chlorine, which is a very reactive metal. The atoms in a compound are always combined in fixed ratios. For example, water always has two hydrogen atoms and one oxygen atom. Glucose, which is a type of sugar, always has 6 carbons, 12 hydrogens, and 6 oxygens. The only way you can separate a compound into its atoms is through a chemical reaction. However, if you break a compound up, you will change the identity of the substance into something else. For example, if you break up water using a chemical reaction, you will end up with hydrogen gas and oxygen gas, and these are not water. A mixture is a combination of two or more substances in any proportion. You can have mixtures of elements, or mixtures of compounds, or mixtures of elements and compounds. We can also have mixtures of larger things. The cereal and milk you eat every day for breakfast, or chicken soup, or those multi-colored Legos, those are all mixtures. What's important about mixtures is that the substances in a mixture do not combine chemically, and they retain their chemical and physical properties. Mixtures can usually be separated into their parts using physical means, which means you don't have to use a chemical reaction. For example, salt water is a mixture of salt and water, one way to separate this mixture is by evaporating the water. The way they make the sea salt that you can buy in a grocery store is by evaporating sea water in salt evaporation ponds like these. The water evaporates and the salt is left behind. In summary, matter can be divided into elements, compounds, and mixtures. Elements can consist of individual atoms or the same atom bonded together in a molecule. Elements are pure substances. A compound is two or more atoms of different elements that are chemically bonded together. It is also a pure substance. A mixture is a combination of two or more substances in any proportion.